My application has several independent "top-level" windows, which all have completely different functions/workflows.
I am currently using ShowDialog() to make a WPF Window modal. The modal window is a child of one of the main windows. However, it is blocking all the top-level windows once it is open. I would like the dialog to block ONLY the parent window it was launched from. Is this possible?
I'm not sure if it matters, but the window that opens the dialog is the initial window of the app--so all other top-level windows are opened from it.
I had the same problem and implemented the modal dialog behavior as described in this post:
http://social.msdn.microsoft.com/Forums/vstudio/en-US/820bf10f-3eaf-43a8-b5ef-b83b2394342c/windowsshowmodal-to-parentowner-window-only-not-entire-application?forum=wpf
I also tried a multiple UI thread approach, but this caused problems with third-party libraries (caliburn micro & telerik wpf controls), since they are not built to be used in multiple UI threads. It is possible to make them work with multiple UI threads, but I prefer a simpler solution...
If you implement the dialog as described, you can not use the DialogResult property anymore, since it would cause a "DialogResult can be set only after Window is created and shown as dialog" exception. Just implement your own property and use it instead.
You need the following windows API reference:
/// <summary>
/// Enables or disables mouse and keyboard input to the specified window or control.
/// When input is disabled, the window does not receive input such as mouse clicks and key presses.
/// When input is enabled, the window receives all input.
/// </summary>
/// <param name="hWnd"></param>
/// <param name="bEnable"></param>
/// <returns></returns>
[DllImport("user32.dll")]
private static extern bool EnableWindow(IntPtr hWnd, bool bEnable);
Then use this:
// get parent window handle
IntPtr parentHandle = (new WindowInteropHelper(window.Owner)).Handle;
// disable parent window
EnableWindow(parentHandle, false);
// when the dialog is closing we want to re-enable the parent
window.Closing += SpecialDialogWindow_Closing;
// wait for the dialog window to be closed
new ShowAndWaitHelper(window).ShowAndWait();
window.Owner.Activate();
This is the event handler which re-enables the parent window, when the dialog is closed:
private void SpecialDialogWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
var win = (Window)sender;
win.Closing -= SpecialDialogWindow_Closing;
IntPtr winHandle = (new WindowInteropHelper(win)).Handle;
EnableWindow(winHandle, false);
if (win.Owner != null)
{
IntPtr parentHandle = (new WindowInteropHelper(win.Owner)).Handle;
// reenable parent window
EnableWindow(parentHandle, true);
}
}
And this is the ShowAndWaitHelper needed to achieve the modal dialog behavior (this blocks the execution of the thread, but still executes the message loop.
private sealed class ShowAndWaitHelper
{
private readonly Window _window;
private DispatcherFrame _dispatcherFrame;
internal ShowAndWaitHelper(Window window)
{
if (window == null)
{
throw new ArgumentNullException("window");
}
_window = window;
}
internal void ShowAndWait()
{
if (_dispatcherFrame != null)
{
throw new InvalidOperationException("Cannot call ShowAndWait while waiting for a previous call to ShowAndWait to return.");
}
_window.Closed += OnWindowClosed;
_window.Show();
_dispatcherFrame = new DispatcherFrame();
Dispatcher.PushFrame(_dispatcherFrame);
}
private void OnWindowClosed(object source, EventArgs eventArgs)
{
if (_dispatcherFrame == null)
{
return;
}
_window.Closed -= OnWindowClosed;
_dispatcherFrame.Continue = false;
_dispatcherFrame = null;
}
}
One option is to start the windows that you don't want affected by the dialog on a different thread. This may result in other issues for your application, but if those windows do really encapsulate different workflows, that may not be an issue. Here is some sample code I wrote to verify that this works:
<Window x:Class="ModalSample.MyWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="{Binding Identifier}" Height="150" Width="150">
<StackPanel>
<TextBox Text="{Binding Identifier}" />
<Button Content="Open Normal Child" Click="OpenNormal_Click" />
<Button Content="Open Independent Child" Click="OpenIndependent_Click" />
<Button Content="Open Modal Child" Click="OpenModal_Click" />
</StackPanel>
</Window>
using System.ComponentModel;
using System.Threading;
using System.Windows;
namespace ModalSample
{
/// <summary>
/// Interaction logic for MyWindow.xaml
/// </summary>
public partial class MyWindow : INotifyPropertyChanged
{
public MyWindow()
{
InitializeComponent();
DataContext = this;
}
private int child = 1;
private string mIdentifier = "Root";
public string Identifier
{
get { return mIdentifier; }
set
{
if (mIdentifier == value) return;
mIdentifier = value;
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs("Identifier"));
}
}
private void OpenNormal_Click(object sender, RoutedEventArgs e)
{
var window = new MyWindow {Identifier = Identifier + "-N" + child++};
window.Show();
}
private void OpenIndependent_Click(object sender, RoutedEventArgs e)
{
var thread = new Thread(() =>
{
var window = new MyWindow {Identifier = Identifier + "-I" + child++};
window.Show();
window.Closed += (sender2, e2) => window.Dispatcher.InvokeShutdown();
System.Windows.Threading.Dispatcher.Run();
});
thread.SetApartmentState(ApartmentState.STA);
thread.Start();
}
private void OpenModal_Click(object sender, RoutedEventArgs e)
{
var window = new MyWindow { Identifier = Identifier + "-M" + child++ };
window.ShowDialog();
}
public event PropertyChangedEventHandler PropertyChanged;
}
}
I sourced this blog post for running a WPF window on a different thread.
Related
I am trying to implement some fade-in and fade-out animations for a user control in WPF. For the fade-in animation I was able to use the Loaded event to accomplish that.
public sealed partial class NowPlayingView : UserControl
{
public Duration AnimationDuration
{
get { return (Duration)GetValue(AnimationDurationProperty); }
set { SetValue(AnimationDurationProperty, value); }
}
public static readonly DependencyProperty AnimationDurationProperty =
DependencyProperty.Register("AnimationDuration", typeof(Duration), typeof(NowPlayingView), new PropertyMetadata(Duration.Automatic));
public NowPlayingView()
{
Opacity = 0;
InitializeComponent();
Loaded += NowPlayingView_Loaded;
Unloaded += NowPlayingView_Unloaded;
}
private void NowPlayingView_Unloaded(object sender, RoutedEventArgs e)
{
DoubleAnimation animation = new(1.0, 0.0, AnimationDuration);
BeginAnimation(OpacityProperty, animation);
}
private void NowPlayingView_Loaded(object sender, RoutedEventArgs e)
{
DoubleAnimation animation = new (0.0, 1.0, AnimationDuration);
BeginAnimation(OpacityProperty, animation);
}
}
I attempted to use the Unloaded event for the fade-out effect only to find out that the event is fired after the UserControl is removed from the visual tree (when the UserControl is no longer visible or accessible). Is there a way to run some code right before the UserControl "closes", something like the OnClosing event of a Window?
EDIT:
For a bit more context, the UserControl acts as a component of a more complex window. It is activated whenever the Property NowPlayingViewModel is not null and deactivated when null (which I do in order to hide the UserControl). It is when I set the ViewModel to null that I want to run the fade-out animation and I would like to keep the code-behind decoupled from other ViewModel logic.
<!-- Now playing View-->
<ContentControl Grid.RowSpan="3" Grid.ColumnSpan="2" Content="{Binding NowPlayingViewModel}">
<ContentControl.Resources>
<DataTemplate DataType="{x:Type viewmodels:NowPlayingViewModel}">
<views:NowPlayingView AnimationDuration="00:00:00.8" />
</DataTemplate>
</ContentControl.Resources>
</ContentControl>
From my testing, I couldn't find any good solution to this so far, though I am open to suggestions that lead to similar behavior.
There is no Closing event in UserControl.. but you can get the parent window when UserControl is loaded and implement the fade-out behavior there..
First, Remove Unloaded += NowPlayingView_Unloaded;
Then, modify the Loaded code a bit..
private Window ParentWindow
{
get
{
DependencyObject parentDepObj = this;
do
{
parentDepObj = VisualTreeHelper.GetParent(parentDepObj);
if (parentDepObj is Window parentWindow) return parentWindow;
} while (parentDepObj != null);
return null;
}
}
private void NowPlayingView_Loaded(object sender, RoutedEventArgs e)
{
DoubleAnimation animation = new(0.0, 1.0, AnimationDuration);
BeginAnimation(OpacityProperty, animation);
var parentWindow = this.ParentOfType<Window>();
parentWindow.Closing += WindowClosing;
}
private void WindowClosing(object sender, CancelEventArgs args)
{
var pw = ParentWindow;
pw.Closing -= WindowClosing;
args.Cancel = true;
var anim = new(1.0, 0.0, AnimationDuration);
anim.Completed += (s, _) => pw.Close();
BeginAnimation(OpacityProperty, anim);
}
Optional Note. You could replace the getter of ParentWindow property with a simple call
private Window ParentWindow => this.ParentOfType<Window>();
Where ParentOfType is an extension function in some public static class Utilities..
public static T ParentOfType<T>(this DependencyObject child) where T : DependencyObject
{
var parentDepObj = child;
do
{
parentDepObj = VisualTreeHelper.GetParent(parentDepObj);
if (parentDepObj is T parent) return parent;
} while (parentDepObj != null);
return null;
}
In my WPF application I would like to subscribe to some event/callbeck/whatever that tells me whenever a dialog window opens (and closes) in my application.
I found the window collection but this is a simple container and it doesn't seem to provide any means of subscription.
I also tried using event handlers but there seems not be an event that tells me what I need.
Any ideas?
One way to do it without a base class is adding a handler to MainWindow deactivated
If a new window is opened, the main window will lose focus = your "new window event"
private readonly List<Window> openWindows = new List<Window>();
public void ApplicationMainWindow_Deactivated(object sender, EventArgs e)
{
foreach (Window window in Application.Current.Windows)
{
if (!openWindows.Contains(window) && window != sender)
{
// Your window code here
window.Closing += PopupWindow_Closing;
openWindows.Add(window);
}
}
}
private void PopupWindow_Closing(object sender, CancelEventArgs e)
{
var window = (Window)sender;
window.Closing -= PopupWindow_Closing;
openWindows.Remove(window);
}
Without creating a Base class for all your windows where you can hook into the opened event (or manually adding the opened event to each window), I'm not sure how you'd be able to know when new windows were create.
There may be a more elegant way, but you could poll the Application.Current.Windows to see if any new windows were created while keeping track of the one's you've found.
Here is a crude example that will demonstrate how to use a DispatchTimer to poll for new windows, keep track of found windows and hook into the closed event.
Code Behind
public partial class MainWindow : Window
{
private DispatcherTimer Timer { get; set; }
public ObservableCollection<Window> Windows { get; private set; }
public MainWindow()
{
InitializeComponent();
// add current Window so we don't add a hook into it
Windows = new ObservableCollection<Window> { this };
Timer = new DispatcherTimer( DispatcherPriority.Background );
Timer.Interval = TimeSpan.FromMilliseconds( 500 );
Timer.Tick += ( _, __ ) => FindNewWindows();
Timer.Start();
this.WindowListBox.ItemsSource = Windows;
this.WindowListBox.DisplayMemberPath = "Title";
}
private void FindNewWindows()
{
foreach( Window window in Application.Current.Windows )
{
if( !Windows.Contains( window ) )
{
window.Closed += OnWatchedWindowClosed;
// inserting at 0 so you can see it in the ListBox
Windows.Insert( 0, window );
Feedback.Text = string.Format( "New Window Found: {0}\r\n{1}",
window.Title, Feedback.Text );
}
}
}
private void OnWatchedWindowClosed( object sender, EventArgs e )
{
var window = (Window)sender;
Windows.Remove( window );
Feedback.Text = string.Format( "Window Closed: {0}\r\n{1}",
window.Title, Feedback.Text );
}
private void CreateWindowButtonClick( object sender, RoutedEventArgs e )
{
string title = string.Format( "New Window {0}", DateTime.Now );
var win = new Window
{
Title = title,
Width = 250,
Height = 250,
Content = title,
};
win.Show();
e.Handled = true;
}
}
XAML
<Grid>
<ListBox Name="WindowListBox"
Width="251"
Height="130"
Margin="12,12,0,0"
HorizontalAlignment="Left"
VerticalAlignment="Top" />
<TextBox Name="Feedback"
Width="479"
Height="134"
Margin="12,148,0,0"
HorizontalAlignment="Left"
VerticalAlignment="Top"
VerticalScrollBarVisibility="Auto" />
<Button Name="CreateWindowButton"
Width="222"
Height="130"
Margin="269,12,0,0"
HorizontalAlignment="Left"
VerticalAlignment="Top"
Click="CreateWindowButtonClick"
Content="Create New Window"
FontSize="20" />
</Grid>
Click away and create as many new windows as you want; then close them. You'll see the feedback as it happens. Granted, there will be a 500ms delay whenever a new window is created since the DispatchTimer's interval is set at 500ms.
You could register a class handler in App.cs as demonstrated here
https://gist.github.com/mwisnicki/3104963
...
EventManager.RegisterClassHandler(typeof(UIElement), FrameworkElement.LoadedEvent, new RoutedEventHandler(OnLoaded), true);
EventManager.RegisterClassHandler(typeof(UIElement), FrameworkElement.UnloadedEvent, new RoutedEventHandler(OnUnloaded), true);
...
private static void OnLoaded(object sender, RoutedEventArgs e)
{
if (sender is Window)
Console.WriteLine("Loaded Window: {0}", sender);
}
private static void OnUnloaded(object sender, RoutedEventArgs e)
{
if (sender is Window)
Console.WriteLine("Unloaded Window: {0}", sender);
}
The link above seems to register an empty handler on instances to make things work properly.
I have never heard of any global open/close event.
It should somehow be possible to do, but that provides that you have control over all windows opening and closing. Like if you build a "base window" (which naturally inherit "Window") that all your dialogs windows inherit from.
Then you clould have a static event on the "base window" which you fire from the base window's opening and closing/closed (or unloaded) events, sending "this" as "sender".
You can attafh to that static event in your App.xaml.cs class.
It's a hack, but it's possible.
Sit Rep
I have a WPF app. In the constructor of the (C#) code-behind I attach a button event-handler. Problem is, it doesn't attach! But if I attach it via clicking a UI button, then the button works fine. Also, of course, if I attach it in the button's XAML it works too.
So, it appears that the prob is attaching the handler in the constructor. It seems to be too early in the process.
App Image
This is what I want, but doesn't attach:
public MainWindow()
{
InitializeComponent();
//...
//
// TEST RADIO BUTTONS
//
// THIS HANDLER DOESN'T ATTACH!
ui_Test.Click += (object sender, RoutedEventArgs e) =>
{
bool localOnly = Convert.ToBoolean(ui_rdoLocal.IsChecked);
bool onlineOnly = Convert.ToBoolean(ui_rdoOnline.IsChecked);
bool both = Convert.ToBoolean(ui_rdoBoth.IsChecked);
string message = "Local: {1}{0}Online: {2}{0}Both: {3}".Put(nl, localOnly, onlineOnly, both);
MessageBox.Show(message);
};
//...
}
And here's the code for a second test button which attaches the above code via a button click. This handler is set in XAML. The handler then works, but I want to attach the handler in C#, not XAML.
<Button Name="ui_Test2" Content="Attach Annonymous Handlers" Margin="30,10" Click="ui_Test2_Click"></Button>
And the method:
/// <summary>
/// Attaches control handlers. Will they attach now? YES!!
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void ui_Test2_Click(object sender, RoutedEventArgs e)
{
ui_Test.Click += (object sndr, RoutedEventArgs rea) =>
{
bool localOnly = Convert.ToBoolean(ui_rdoLocal.IsChecked);
bool onlineOnly = Convert.ToBoolean(ui_rdoOnline.IsChecked);
bool both = Convert.ToBoolean(ui_rdoBoth.IsChecked);
string message = "Local: {1}{0}Online: {2}{0}Both: {3}".Put(nl, localOnly, onlineOnly, both);
MessageBox.Show(message);
};
}
Thx in advance for any help!
Gregg
Try to attach handler after calling InitializeComponent(); in constructor.
How one can show dialog window (e.g. login / options etc.) before the main window?
Here is what I tried (it apparently has once worked, but not anymore):
XAML:
<Application ...
Startup="Application_Startup">
Application:
public partial class App : Application
{
private void Application_Startup(object sender, StartupEventArgs e)
{
Window1 myMainWindow = new Window1();
DialogWindow myDialogWindow = new DialogWindow();
myDialogWindow.ShowDialog();
}
}
Outcome: myDialogWindow is shown first. When it is closed, the Window1 is shown as expected. But as I close Window1 the application does not close at all.
Here's the full solution that worked for me:
In App.xaml, I remove the StartupUri stuff, and add a Startup handler:
<Application x:Class="MyNamespace.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Startup="ApplicationStart">
</Application>
In App.xaml.cs, I define the handler as follows:
public partial class App
{
private void ApplicationStart(object sender, StartupEventArgs e)
{
//Disable shutdown when the dialog closes
Current.ShutdownMode = ShutdownMode.OnExplicitShutdown;
var dialog = new DialogWindow();
if (dialog.ShowDialog() == true)
{
var mainWindow = new MainWindow(dialog.Data);
//Re-enable normal shutdown mode.
Current.ShutdownMode = ShutdownMode.OnMainWindowClose;
Current.MainWindow = mainWindow;
mainWindow.Show();
}
else
{
MessageBox.Show("Unable to load data.", "Error", MessageBoxButton.OK);
Current.Shutdown(-1);
}
}
}
Okay apologizes, here is the solution:
My original question worked almost, only one thing to add, remove the StartupUri from the Application XAML and after that add the Show to main window.
That is:
<Application x:Class="DialogBeforeMainWindow.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Startup="Application_Startup">
Above, StartupUri removed.
Add myMainWindow.Show() too:
public partial class App : Application
{
private void Application_Startup(object sender, StartupEventArgs e)
{
Window1 myMainWindow = new Window1();
DialogWindow myDialogWindow = new DialogWindow();
myDialogWindow.ShowDialog();
myMainWindow.Show();
}
}
WPF sets App.Current.MainWindow to the first window opened. If you have control over the secondary window constructor, just set App.Current.MainWindow = Null there. Once your main window is constructed, it will be assigned to the App.Current.MainWindow property as expected without any intervention.
public partial class TraceWindow : Window
{
public TraceWindow()
{
InitializeComponent();
if (App.Current.MainWindow == this)
{
App.Current.MainWindow = null;
}
}
}
If you don't have access, you can still set MainWindow within the main window's constructor.
If you put Application.Current.ShutdownMode = ShutdownMode.OnExplicitShutdown; into the constructor of the dialog, and add
protected override void OnClosed(EventArgs e) {
base.OnClosed(e);
Application.Current.ShutdownMode = ShutdownMode.OnMainWindowClose;
}
into the dialog class, you don't need to worry about making any changes to the default behaviour of the application. This works great if you want to just snap a login screen into an already-existing app without tweaking the startup procedures.
So you want to show one window, then another, but close down the app when that window is closed? You may need to set the ShutdownMode to OnMainWindowClose and set the MainWindow to Window1, along the lines ok:
Window1 myMainWindow = new Window1();
Application.Current.ShutdownMode = ShutdownMode.OnMainWindowClose;
Application.Current.MainWindow = myMainWindow;
DialogWindow myDialogWindow = new DialogWindow();
myDialogWindow.ShowDialog();
here, do it like this. this will actaully change your main window and will work properly w/o having to change settings of your application object.
make sure to remove the event handler for application startup and to set your StartupUri in your app.xaml file.
public partial class App : Application
{
bool init = false;
protected override void OnActivated(EventArgs e)
{
base.OnActivated(e);
if (!init)
{
this.MainWindow.Closing += new System.ComponentModel.CancelEventHandler(MainWindow_Closing);
init = true;
}
}
void MainWindow_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
Window toClose = this.MainWindow;
this.MainWindow = new Window2();
this.MainWindow.Show();
}
}
I have the same issue when i need to disloag a login screen before my main window
In you main window cunstructor add these lines
Application.Current.MainWindow = this;
Application.Current.ShutdownMode = ShutdownMode.OnMainWindowClose;
Resolve the main window or just call var mainWindow = new MainWindow()
Call the loginScreen.Show() or loginScreen.ShowDialog()
I've got a WPF application with a Treeview control.
When the user clicks a node on the tree, other TextBox, ComboBox, etc. controls on the page are populated with appropriate values.
The user can then make changes to those values and save his or her changes by clicking a Save button.
However, if the user selects a different Treeview node without saving his or her changes, I want to display a warning and an opportunity to cancel that selection.
MessageBox: Continue and discard your unsaved changes? OK/Cancel http://img522.imageshack.us/img522/2897/discardsj3.gif
XAML...
<TreeView Name="TreeViewThings"
...
TreeViewItem.Unselected="TreeViewThings_Unselected"
TreeViewItem.Selected="TreeViewThings_Selected" >
Visual Basic...
Sub TreeViewThings_Unselected(ByVal sender As System.Object, _
ByVal e As System.Windows.RoutedEventArgs)
Dim OldThing As Thing = DirectCast(e.OriginalSource.DataContext, Thing)
If CancelDueToUnsavedChanges(OldThing) Then
'put canceling code here
End If
End Sub
Sub TreeViewThings_Selected(ByVal sender As System.Object, _
ByVal e As System.Windows.RoutedEventArgs)
Dim NewThing As Thing = DirectCast(e.OriginalSource.DataContext, Thing)
PopulateControlsFromThing(NewThing)
End Sub
How can I cancel those unselect/select events?
Update: I've asked a follow-up question...
How do I properly handle a PreviewMouseDown event with a MessageBox confirmation?
UPDATE
Realized I could put the logic in SelectedItemChanged instead. A little cleaner solution.
Xaml
<TreeView Name="c_treeView"
SelectedItemChanged="c_treeView_SelectedItemChanged">
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<Setter Property="IsSelected" Value="{Binding Path=IsSelected, Mode=TwoWay}" />
</Style>
</TreeView.ItemContainerStyle>
</TreeView>
Code behind. I have some classes that is my ItemsSource of the TreeView so I made an interface (MyInterface) that exposes the IsSelected property for all of them.
private MyInterface m_selectedTreeViewItem = null;
private void c_treeView_SelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
if (m_selectedTreeViewItem != null)
{
if (e.NewValue == m_selectedTreeViewItem)
{
// Will only end up here when reversing item
// Without this line childs can't be selected
// twice if "No" was pressed in the question..
c_treeView.Focus();
}
else
{
if (MessageBox.Show("Change TreeViewItem?",
"Really change",
MessageBoxButton.YesNo,
MessageBoxImage.Question) != MessageBoxResult.Yes)
{
EventHandler eventHandler = null;
eventHandler = new EventHandler(delegate
{
c_treeView.LayoutUpdated -= eventHandler;
m_selectedTreeViewItem.IsSelected = true;
});
// Will be fired after SelectedItemChanged, to early to change back here
c_treeView.LayoutUpdated += eventHandler;
}
else
{
m_selectedTreeViewItem = e.NewValue as MyInterface;
}
}
}
else
{
m_selectedTreeViewItem = e.NewValue as MyInterface;
}
}
I haven't found any situation where it doesn't revert back to the previous item upon pressing "No".
I had to solve the same problem, but in multiple treeviews in my application. I derived TreeView and added event handlers, partly using Meleak's solution and partly using the extension methods from this forum: http://forums.silverlight.net/t/65277.aspx/1/10
I thought I'd share my solution with you, so here is my complete reusable TreeView that handles "cancel node change":
public class MyTreeView : TreeView
{
public static RoutedEvent PreviewSelectedItemChangedEvent;
public static RoutedEvent SelectionCancelledEvent;
static MyTreeView()
{
PreviewSelectedItemChangedEvent = EventManager.RegisterRoutedEvent("PreviewSelectedItemChanged", RoutingStrategy.Bubble,
typeof(RoutedPropertyChangedEventHandler<object>), typeof(MyTreeView));
SelectionCancelledEvent = EventManager.RegisterRoutedEvent("SelectionCancelled", RoutingStrategy.Bubble,
typeof(RoutedEventHandler), typeof(MyTreeView));
}
public event RoutedPropertyChangedEventHandler<object> PreviewSelectedItemChanged
{
add { AddHandler(PreviewSelectedItemChangedEvent, value); }
remove { RemoveHandler(PreviewSelectedItemChangedEvent, value); }
}
public event RoutedEventHandler SelectionCancelled
{
add { AddHandler(SelectionCancelledEvent, value); }
remove { RemoveHandler(SelectionCancelledEvent, value); }
}
private object selectedItem = null;
protected override void OnSelectedItemChanged(RoutedPropertyChangedEventArgs<object> e)
{
if (e.NewValue == selectedItem)
{
this.Focus();
var args = new RoutedEventArgs(SelectionCancelledEvent);
RaiseEvent(args);
}
else
{
var args = new RoutedPropertyChangedEventArgs<object>(e.OldValue, e.NewValue, PreviewSelectedItemChangedEvent);
RaiseEvent(args);
if (args.Handled)
{
EventHandler eventHandler = null;
eventHandler = delegate
{
this.LayoutUpdated -= eventHandler;
var treeViewItem = this.ContainerFromItem(selectedItem);
if (treeViewItem != null)
treeViewItem.IsSelected = true;
};
this.LayoutUpdated += eventHandler;
}
else
{
selectedItem = this.SelectedItem;
base.OnSelectedItemChanged(e);
}
}
}
}
public static class TreeViewExtensions
{
public static TreeViewItem ContainerFromItem(this TreeView treeView, object item)
{
if (item == null) return null;
var containerThatMightContainItem = (TreeViewItem)treeView.ItemContainerGenerator.ContainerFromItem(item);
return containerThatMightContainItem ?? ContainerFromItem(treeView.ItemContainerGenerator, treeView.Items, item);
}
private static TreeViewItem ContainerFromItem(ItemContainerGenerator parentItemContainerGenerator, ItemCollection itemCollection, object item)
{
foreach (var child in itemCollection)
{
var parentContainer = (TreeViewItem)parentItemContainerGenerator.ContainerFromItem(child);
var containerThatMightContainItem = (TreeViewItem)parentContainer.ItemContainerGenerator.ContainerFromItem(item);
if (containerThatMightContainItem != null)
return containerThatMightContainItem;
var recursionResult = ContainerFromItem(parentContainer.ItemContainerGenerator, parentContainer.Items, item);
if (recursionResult != null)
return recursionResult;
}
return null;
}
}
Here is an example of usage (codebehind for window containing a MyTreeView):
private void theTreeView_PreviewSelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
if (e.OldValue != null)
e.Handled = true;
}
private void theTreeView_SelectionCancelled(object sender, RoutedEventArgs e)
{
MessageBox.Show("Cancelled");
}
After choosing the first node in the treeview, all other node changes are cancelled and a message box is displayed.
You can't actually put your logic into the OnSelectedItemChanged Method, if the logic is there the Selected Item has actually already changed.
As suggested by another poster, the PreviewMouseDown handler is a better spot to implement the logic, however, a fair amount of leg work still needs to be done.
Below is my 2 cents:
First the TreeView that I have implemented:
public class MyTreeView : TreeView
{
static MyTreeView( )
{
DefaultStyleKeyProperty.OverrideMetadata(
typeof(MyTreeView),
new FrameworkPropertyMetadata(typeof(TreeView)));
}
// Register a routed event, note this event uses RoutingStrategy.Tunnel. per msdn docs
// all "Preview" events should use tunneling.
// http://msdn.microsoft.com/en-us/library/system.windows.routedevent.routingstrategy.aspx
public static RoutedEvent PreviewSelectedItemChangedEvent = EventManager.RegisterRoutedEvent(
"PreviewSelectedItemChanged",
RoutingStrategy.Tunnel,
typeof(CancelEventHandler),
typeof(MyTreeView));
// give CLR access to routed event
public event CancelEventHandler PreviewSelectedItemChanged
{
add
{
AddHandler(PreviewSelectedItemChangedEvent, value);
}
remove
{
RemoveHandler(PreviewSelectedItemChangedEvent, value);
}
}
// override PreviewMouseDown
protected override void OnPreviewMouseDown(MouseButtonEventArgs e)
{
// determine which item is going to be selected based on the current mouse position
object itemToBeSelected = this.GetObjectAtPoint<TreeViewItem>(e.GetPosition(this));
// selection doesn't change if the target point is null (beyond the end of the list)
// or if the item to be selected is already selected.
if (itemToBeSelected != null && itemToBeSelected != SelectedItem)
{
bool shouldCancel;
// call our new event
OnPreviewSelectedItemChanged(out shouldCancel);
if (shouldCancel)
{
// if we are canceling the selection, mark this event has handled and don't
// propogate the event.
e.Handled = true;
return;
}
}
// otherwise we want to continue normally
base.OnPreviewMouseDown(e);
}
protected virtual void OnPreviewSelectedItemChanged(out bool shouldCancel)
{
CancelEventArgs e = new CancelEventArgs( );
if (PreviewSelectedItemChangedEvent != null)
{
// Raise our event with our custom CancelRoutedEventArgs
RaiseEvent(new CancelRoutedEventArgs(PreviewSelectedItemChangedEvent, e));
}
shouldCancel = e.Cancel;
}
}
some extension methods to support the TreeView finding the object under the mouse.
public static class ItemContainerExtensions
{
// get the object that exists in the container at the specified point.
public static object GetObjectAtPoint<ItemContainer>(this ItemsControl control, Point p)
where ItemContainer : DependencyObject
{
// ItemContainer - can be ListViewItem, or TreeViewItem and so on(depends on control)
ItemContainer obj = GetContainerAtPoint<ItemContainer>(control, p);
if (obj == null)
return null;
// it is worth noting that the passed _control_ may not be the direct parent of the
// container that exists at this point. This can be the case in a TreeView, where the
// parent of a TreeViewItem may be either the TreeView or a intermediate TreeViewItem
ItemsControl parentGenerator = obj.GetParentItemsControl( );
// hopefully this isn't possible?
if (parentGenerator == null)
return null;
return parentGenerator.ItemContainerGenerator.ItemFromContainer(obj);
}
// use the VisualTreeHelper to find the container at the specified point.
public static ItemContainer GetContainerAtPoint<ItemContainer>(this ItemsControl control, Point p)
where ItemContainer : DependencyObject
{
HitTestResult result = VisualTreeHelper.HitTest(control, p);
DependencyObject obj = result.VisualHit;
while (VisualTreeHelper.GetParent(obj) != null && !(obj is ItemContainer))
{
obj = VisualTreeHelper.GetParent(obj);
}
// Will return null if not found
return obj as ItemContainer;
}
// walk up the visual tree looking for the nearest ItemsControl parent of the specified
// depObject, returns null if one isn't found.
public static ItemsControl GetParentItemsControl(this DependencyObject depObject)
{
DependencyObject obj = VisualTreeHelper.GetParent(depObject);
while (VisualTreeHelper.GetParent(obj) != null && !(obj is ItemsControl))
{
obj = VisualTreeHelper.GetParent(obj);
}
// will return null if not found
return obj as ItemsControl;
}
}
and last, but not least the custom EventArgs that leverage the RoutedEvent subsystem.
public class CancelRoutedEventArgs : RoutedEventArgs
{
private readonly CancelEventArgs _CancelArgs;
public CancelRoutedEventArgs(RoutedEvent #event, CancelEventArgs cancelArgs)
: base(#event)
{
_CancelArgs = cancelArgs;
}
// override the InvokeEventHandler because we are going to pass it CancelEventArgs
// not the normal RoutedEventArgs
protected override void InvokeEventHandler(Delegate genericHandler, object genericTarget)
{
CancelEventHandler handler = (CancelEventHandler)genericHandler;
handler(genericTarget, _CancelArgs);
}
// the result
public bool Cancel
{
get
{
return _CancelArgs.Cancel;
}
}
}
Instead of selecting for Selected/Unselected, a better route might be to hook into PreviewMouseDown. The preblem with handling a Selected and Unselected event is that the event has already occurred when you receive the notification. There is nothing to cancel because it's already happened.
On the other hand, Preview events are cancelable. It's not the exact event you want but it does give you the oppuritunity to prevent the user from selecting a different node.
You can't cancel the event like you can, for example, a Closing event. But you can undo it if you cache the last selected value. The secret is you have to change the selection without re-firing the SelectionChanged event. Here's an example:
private object _LastSelection = null;
private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (IsUpdated)
{
MessageBoxResult result = MessageBox.Show("The current record has been modified. Are you sure you want to navigate away? Click Cancel to continue editing. If you click OK all changes will be lost.", "Warning", MessageBoxButton.OKCancel, MessageBoxImage.Hand);
switch (result)
{
case MessageBoxResult.Cancel:
e.Handled = true;
// disable event so this doesn't go into an infinite loop when the selection is changed to the cached value
PersonListView.SelectionChanged -= new SelectionChangedEventHandler(OnSelectionChanged);
PersonListView.SelectedItem = _LastSelection;
PersonListView.SelectionChanged += new SelectionChangedEventHandler(OnSelectionChanged);
return;
case MessageBoxResult.OK:
// revert the object to the original state
LocalDataContext.Persons.GetOriginalEntityState(_LastSelection).CopyTo(_LastSelection);
IsUpdated = false;
Refresh();
break;
default:
throw new ApplicationException("Invalid response.");
}
}
// cache the selected item for undo
_LastSelection = PersonListView.SelectedItem;
}
CAMS_ARIES:
XAML:
code :
private bool ManejarSeleccionNodoArbol(Object origen)
{
return true; // with true, the selected nodo don't change
return false // with false, the selected nodo change
}
private void Arbol_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
if (e.Source is TreeViewItem)
{
e.Handled = ManejarSeleccionNodoArbol(e.Source);
}
}
private void Arbol_PreviewKeyDown(object sender, KeyEventArgs e)
{
if (e.Source is TreeViewItem)
{
e.Handled=ManejarSeleccionNodoArbol(e.Source);
}
}
Since the SelectedItemChanged event is triggered after the SelectedItem has already changed, you can't really cancel the event at this point.
What you can do is listen for mouse-clicks and cancel them before the SelectedItem gets changed.
You could create your custom control that derives from TreeView and then override the OnSelectedItemChanged method.
Before calling the base, you could first fire a custom event with a CancelEventArgs parameter. If the parameter.Cancel become true, then don't call the base, but select the old item instead (be careful that the OnSelectedItemChanged will be called again).
Not the best solution, but at least this keeps the logic inside the tree control, and there is not chance that the selection change event fires more than it's needed. Also, you don't need to care if the user clicked the tree, used the keyboard or maybe the selection changed programatically.
I solved this problem for 1 tree view and display of 1 document at a time. This solution is based on an attachable behavior that can be attached to a normal treeview:
<TreeView Grid.Column="0"
ItemsSource="{Binding TreeViewItems}"
behav:TreeViewSelectionChangedBehavior.ChangedCommand="{Binding SelectItemChangedCommand}"
>
<TreeView.ItemTemplate>
<HierarchicalDataTemplate ItemsSource="{Binding Children}">
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Name}"
ToolTipService.ShowOnDisabled="True"
VerticalAlignment="Center" Margin="3" />
</StackPanel>
</HierarchicalDataTemplate>
</TreeView.ItemTemplate>
<TreeView.ItemContainerStyle>
<Style TargetType="{x:Type TreeViewItem}">
<Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
<Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
</Style>
</TreeView.ItemContainerStyle>
</TreeView>
and the code for the behavior is this:
/// <summary>
/// Source:
/// http://stackoverflow.com/questions/1034374/drag-and-drop-in-mvvm-with-scatterview
/// http://social.msdn.microsoft.com/Forums/de-DE/wpf/thread/21bed380-c485-44fb-8741-f9245524d0ae
///
/// Attached behaviour to implement the SelectionChanged command/event via delegate command binding or routed commands.
/// </summary>
public static class TreeViewSelectionChangedBehavior
{
#region fields
/// <summary>
/// Field of attached ICommand property
/// </summary>
private static readonly DependencyProperty ChangedCommandProperty = DependencyProperty.RegisterAttached(
"ChangedCommand",
typeof(ICommand),
typeof(TreeViewSelectionChangedBehavior),
new PropertyMetadata(null, OnSelectionChangedCommandChange));
/// <summary>
/// Implement backing store for UndoSelection dependency proeprty to indicate whether selection should be
/// cancelled via MessageBox query or not.
/// </summary>
public static readonly DependencyProperty UndoSelectionProperty =
DependencyProperty.RegisterAttached("UndoSelection",
typeof(bool),
typeof(TreeViewSelectionChangedBehavior),
new PropertyMetadata(false, OnUndoSelectionChanged));
#endregion fields
#region methods
#region ICommand changed methods
/// <summary>
/// Setter method of the attached ChangedCommand <seealso cref="ICommand"/> property
/// </summary>
/// <param name="source"></param>
/// <param name="value"></param>
public static void SetChangedCommand(DependencyObject source, ICommand value)
{
source.SetValue(ChangedCommandProperty, value);
}
/// <summary>
/// Getter method of the attached ChangedCommand <seealso cref="ICommand"/> property
/// </summary>
/// <param name="source"></param>
/// <returns></returns>
public static ICommand GetChangedCommand(DependencyObject source)
{
return (ICommand)source.GetValue(ChangedCommandProperty);
}
#endregion ICommand changed methods
#region UndoSelection methods
public static bool GetUndoSelection(DependencyObject obj)
{
return (bool)obj.GetValue(UndoSelectionProperty);
}
public static void SetUndoSelection(DependencyObject obj, bool value)
{
obj.SetValue(UndoSelectionProperty, value);
}
#endregion UndoSelection methods
/// <summary>
/// This method is hooked in the definition of the <seealso cref="ChangedCommandProperty"/>.
/// It is called whenever the attached property changes - in our case the event of binding
/// and unbinding the property to a sink is what we are looking for.
/// </summary>
/// <param name="d"></param>
/// <param name="e"></param>
private static void OnSelectionChangedCommandChange(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
TreeView uiElement = d as TreeView; // Remove the handler if it exist to avoid memory leaks
if (uiElement != null)
{
uiElement.SelectedItemChanged -= Selection_Changed;
var command = e.NewValue as ICommand;
if (command != null)
{
// the property is attached so we attach the Drop event handler
uiElement.SelectedItemChanged += Selection_Changed;
}
}
}
/// <summary>
/// This method is called when the selection changed event occurs. The sender should be the control
/// on which this behaviour is attached - so we convert the sender into a <seealso cref="UIElement"/>
/// and receive the Command through the <seealso cref="GetChangedCommand"/> getter listed above.
///
/// The <paramref name="e"/> parameter contains the standard EventArgs data,
/// which is unpacked and reales upon the bound command.
///
/// This implementation supports binding of delegate commands and routed commands.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private static void Selection_Changed(object sender, RoutedPropertyChangedEventArgs<object> e)
{
var uiElement = sender as TreeView;
// Sanity check just in case this was somehow send by something else
if (uiElement == null)
return;
ICommand changedCommand = TreeViewSelectionChangedBehavior.GetChangedCommand(uiElement);
// There may not be a command bound to this after all
if (changedCommand == null)
return;
// Check whether this attached behaviour is bound to a RoutedCommand
if (changedCommand is RoutedCommand)
{
// Execute the routed command
(changedCommand as RoutedCommand).Execute(e.NewValue, uiElement);
}
else
{
// Execute the Command as bound delegate
changedCommand.Execute(e.NewValue);
}
}
/// <summary>
/// Executes when the bound boolean property indicates that a user should be asked
/// about changing a treeviewitem selection instead of just performing it.
/// </summary>
/// <param name="d"></param>
/// <param name="e"></param>
private static void OnUndoSelectionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
TreeView uiElement = d as TreeView; // Remove the handler if it exist to avoid memory leaks
if (uiElement != null)
{
uiElement.PreviewMouseDown -= uiElement_PreviewMouseDown;
var command = (bool)e.NewValue;
if (command == true)
{
// the property is attached so we attach the Drop event handler
uiElement.PreviewMouseDown += uiElement_PreviewMouseDown;
}
}
}
/// <summary>
/// Based on the solution proposed here:
/// Source: http://stackoverflow.com/questions/20244916/wpf-treeview-selection-change
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private static void uiElement_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
// first did the user click on a tree node?
var source = e.OriginalSource as DependencyObject;
while (source != null && !(source is TreeViewItem))
source = VisualTreeHelper.GetParent(source);
var itemSource = source as TreeViewItem;
if (itemSource == null)
return;
var treeView = sender as TreeView;
if (treeView == null)
return;
bool undoSelection = TreeViewSelectionChangedBehavior.GetUndoSelection(treeView);
if (undoSelection == false)
return;
// Cancel the attempt to select an item.
var result = MessageBox.Show("The current document has unsaved data. Do you want to continue without saving data?", "Are you really sure?",
MessageBoxButton.YesNo, MessageBoxImage.Question, MessageBoxResult.No);
if (result == MessageBoxResult.No)
{
// Cancel the attempt to select a differnet item.
e.Handled = true;
}
else
{
// Lets disable this for a moment, otherwise, we'll get into an event "recursion"
treeView.PreviewMouseDown -= uiElement_PreviewMouseDown;
// Select the new item - make sure a SelectedItemChanged event is fired in any case
// Even if this means that we have to deselect/select the one and the same item
if (itemSource.IsSelected == true )
itemSource.IsSelected = false;
itemSource.IsSelected = true;
// Lets enable this to get back to business for next selection
treeView.PreviewMouseDown += uiElement_PreviewMouseDown;
}
}
#endregion methods
}
In this example I am showing a blocking message box in order to block the PreviewMouseDown event when it occurs. The event is then handled to signal that selection is cancelled or it is not handled to let the treeview itself handle the event by selecting the item that is about to be selected.
The behavior then invokes a bound command in the viewmodel if the user decides to continue anyway (PreviewMouseDown event is not handled by attached behavior and bound command is invoked.
I guess the message box showing could be done in other ways but I think its essential here to block the event when it happens since its otherwise not possible to cancel it(?). So, the only improve I could possible think off about this code is to bind some strings to make the displayed message configurable.
I have written an article that contains a downloadable sample since this is otherwise a difficult area to explain (one has to make many assumptions about missing parts that and the may not always be shared by all readers)
Here is an article that contains my results:
http://www.codeproject.com/Articles/995629/Cancelable-TreeView-Navigation-for-Documents-in-WP
Please comment on this solution and let me know if you see room for improvement.