I have the following code:
ControlTemplate ct = (ControlTemplate)XamlReader.Load(validXmlString);
Now I need to obtain the control that this template created, in my case, a Button. I have searched far and wide and can't find a simple explanation for how this is done.
Please note that for some unexplained reason, Microsoft provided a FindControl() method for ControlTemplate in WPF, but not in Silverlight. I've read that this can be done with the VisualTreeHelper, but I have yet to see an explanation for how.
Below you will find an example that loops through the Visual Tree recursively and finds all buttons adding them to a collection. You can check the name of the button etc.. and do what you need to do. I just used a collection as an example, as I found a quick sample on it.
public MainPage()
{
InitializeComponent();
this.Loaded += new RoutedEventHandler(MainPage_Loaded);
}
void MainPage_Loaded(object sender, RoutedEventArgs e)
{
List<UIElement> buttons = new List<UIElement>();
GetChildren(this, typeof(Button), ref buttons);
}
private void GetChildren(UIElement parent, Type targetType, ref List<UIElement> children)
{
int count = VisualTreeHelper.GetChildrenCount(parent);
if (count > 0)
{
for (int i = 0; i < count; i++)
{
UIElement child = (UIElement)VisualTreeHelper.GetChild(parent, i);
if (child.GetType() == targetType)
{
//DO something with the button in the example added to a collection. You can also verify the name and perform the action you wish.
children.Add(child);
}
GetChildren(child, targetType, ref children);
}
}
}
Hope this helps
Related
I need to add some decoration to the contents of a WPF TextBox control. That works fine basically, I can get the position of specified character indices and layout my other elements accordingly. But it all breaks when the TextBox is scrolled. My layout positions don't match with the displayed text anymore because it has moved elsewhere.
Now I'm pretty surprised that the TextBox class doesn't provide any information about its scrolling state, nor any events when the scrolling has changed. What can I do now?
I used Snoop to find out whether there is some scrolling sub-element that I could ask, but the ScrollContentPresenter also doesn't have any scrolling information available. I'd really like to put my decoration elements right into the scrolled area so that the scrolling can affect them, too, but there can only be a single content control and that's one of the TextBox internals already.
I'm not sure how to capture an event when the textbox has been scrolled (probably use narohi's answer for that), but there is a simple way to see what the current scroll position is:
// Gets or sets the vertical scroll position.
textBox.VerticalOffset
(From http://msdn.microsoft.com/en-us/library/system.windows.controls.primitives.textboxbase.verticaloffset(v=vs.100).aspx)
I'm using it to see if the textbox is scrolled to the end, like this:
public static bool IsScrolledToEnd(this TextBox textBox)
{
return textBox.VerticalOffset + textBox.ViewportHeight == textBox.ExtentHeight;
}
You can get the ScrollViewer with this method by passing in your textbox as the argument and the type ScrollView. Then you may subscribe to the ScrollChanged event.
public static T FindDescendant<T>(DependencyObject obj) where T : DependencyObject
{
if (obj == null) return default(T);
int numberChildren = VisualTreeHelper.GetChildrenCount(obj);
if (numberChildren == 0) return default(T);
for (int i = 0; i < numberChildren; i++)
{
DependencyObject child = VisualTreeHelper.GetChild(obj, i);
if (child is T)
{
return (T)(object)child;
}
}
for (int i = 0; i < numberChildren; i++)
{
DependencyObject child = VisualTreeHelper.GetChild(obj, i);
var potentialMatch = FindDescendant<T>(child);
if (potentialMatch != default(T))
{
return potentialMatch;
}
}
return default(T);
}
Example:
public MainWindow()
{
InitializeComponent();
Loaded += new RoutedEventHandler(MainWindow_Loaded);
}
void MainWindow_Loaded(object sender, RoutedEventArgs e)
{
ScrollViewer s = FindDescendant<ScrollViewer>(txtYourTextBox);
s.ScrollChanged += new ScrollChangedEventHandler(s_ScrollChanged);
}
void s_ScrollChanged(object sender, ScrollChangedEventArgs e)
{
// check event args for information needed
}
With each loop iteration, I want to visually update the text of a textblock. My problem is that the WPF window or control does not visually refresh until the loop is complete.
for (int i = 0; i < 50; i++)
{
System.Threading.Thread.Sleep(100);
myTextBlock.Text = i.ToString();
}
In VB6, I would call DoEvents() or control.Refresh. At the moment I'd just like a quick and dirty solution similar to DoEvents(), but I'd also like to know about alternatives or the "right" way to do this. Is there a simple binding statement I could add? What is the syntax?
Thanks in advance.
If you really want the quick and dirty implementation and don't care about maintaining the product in the future or about the user experience, you can just add a reference to System.Windows.Forms and call System.Windows.Forms.Application.DoEvents():
for (int i = 0; i < 50; i++)
{
System.Threading.Thread.Sleep(100);
MyTextBlock.Text = i.ToString();
System.Windows.Forms.Application.DoEvents();
}
The downside is that it's really really bad. You're going to lock up the UI during the Thread.Sleep(), which annoys the user, and you could end up with unpredictable results depending on the complexity of the program (I have seen one application where two methods were running on the UI thread, each one calling DoEvents() repeatedly...).
This is how it should be done:
Any time your application has to wait for something to happen (ie a disk read, a web service call, or a Sleep()), it should be on a separate thread.
You should not set TextBlock.Text manually - bind it to a property and implement INotifyPropertyChanged.
Here is an example showing the functionality you've asked for. It only takes a few seconds longer to write and it's so much easier to work with - and it doesn't lock up the UI.
Xaml:
<StackPanel>
<TextBlock Name="MyTextBlock" Text="{Binding Path=MyValue}"></TextBlock>
<Button Click="Button_Click">OK</Button>
</StackPanel>
CodeBehind:
public partial class MainWindow : Window, INotifyPropertyChanged
{
public MainWindow()
{
InitializeComponent();
this.DataContext = this;
}
private void Button_Click(object sender, RoutedEventArgs e)
{
Task.Factory.StartNew(() =>
{
for (int i = 0; i < 50; i++)
{
System.Threading.Thread.Sleep(100);
MyValue = i.ToString();
}
});
}
private string myValue;
public string MyValue
{
get { return myValue; }
set
{
myValue = value;
RaisePropertyChanged("MyValue");
}
}
private void RaisePropertyChanged(string propName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
public event PropertyChangedEventHandler PropertyChanged;
}
The code might seem a bit complicated, but it's a cornerstone of WPF, and it comes together with a bit of practice - it's well worth learning.
I tried the solution exposed here and it didn't work for me until I added the following:
Create an extension method and make sure you reference its containing assembly from your project.
public static void Refresh(this UIElement uiElement){
uiElement.Dispatcher.Invoke(DispatcherPriority.Background, new Action( () => { }));
}
Then call it right after RaisePropertyChanged:
RaisePropertyChanged("MyValue");
myTextBlock.Refresh();
That will force the UI thread to take control for a small while and dispatch any pending changes on the UI element.
This is how you would do it normally:
ThreadPool.QueueUserWorkItem(ignored =>
{
for (int i = 0; i < 50; i++) {
System.Threading.Thread.Sleep(100);
myTextBlock.Dispatcher.BeginInvoke(
new Action(() => myTextBlock.Text = i.ToString()));
}
});
This delegates the operation to a worker pool thread, which allows your UI thread to process messages (and keeps your UI from freezing). Because the worker thread cannot access myTextBlock directly, it needs to use BeginInvoke.
Although this approach is not "the WPF way" to do things, there's nothing wrong with it (and indeed, I don't believe there's any alternative with this little code). But another way to do things would go like this:
Bind the Text of the TextBlock to a property of some object that implements INotifyPropertyChanged
From within the loop, set that property to the value you want; the changes will be propagated to the UI automatically
No need for threads, BeginInvoke, or anything else
If you already have an object and the UI has access to it, this is as simple as writing Text="{Binding MyObject.MyProperty}".
Update: For example, let's assume you have this:
class Foo : INotifyPropertyChanged // you need to implement the interface
{
private int number;
public int Number {
get { return this.number; }
set {
this.number = value;
// Raise PropertyChanged here
}
}
}
class MyWindow : Window
{
public Foo PropertyName { get; set; }
}
The binding would be done like this in XAML:
<TextBlock Text="{Binding PropertyName.Number}" />
You can do Dispatcher.BeginInvoke in order to do a thread context-switch so that the rendering thread could do its job.
However, this is not the right way for such things. You should use Animation + Binding for things like that, as this is the hack-free way of doing things like that in WPF.
for (int i = 0; i < 50; i++)
{
System.Threading.Thread.Sleep(100);
myTextBlock.Text = i.ToString();
}
Running the above code inside a background worker component and using a binding updatesourcetrigeer as propertychanged will reflect the changes immediately in the UI control.
I'm working on making an app come back nicely from being tombstoned. The app contains large listboxes, so I'd ideally like to scroll back to wherever the user was while they were scrolling around those listboxes.
It's easy to jump back to a particular SelectedItem - unfortunately for me, my app never needs the user to actually select an item, they're just scrolling through them. What I really want is some sort of MyListbox.ScrollPositionY but it doesn't seem to exist.
Any ideas?
Chris
You need to get hold of the ScrollViewer that is used by the ListBox internally so you can grab the value of the VerticalOffset property and subsequently call the SetVerticalOffset method.
This requires that you reach down from the ListBox through the Visual tree that makes up its internals.
I use this handy extension class which you should add to your project (I've gotta put this up on a blog because I keep repeating it):-
public static class VisualTreeEnumeration
{
public static IEnumerable<DependencyObject> Descendents(this DependencyObject root, int depth)
{
int count = VisualTreeHelper.GetChildrenCount(root);
for (int i = 0; i < count; i++)
{
var child = VisualTreeHelper.GetChild(root, i);
yield return child;
if (depth > 0)
{
foreach (var descendent in Descendents(child, --depth))
yield return descendent;
}
}
}
public static IEnumerable<DependencyObject> Descendents(this DependencyObject root)
{
return Descendents(root, Int32.MaxValue);
}
public static IEnumerable<DependencyObject> Ancestors(this DependencyObject root)
{
DependencyObject current = VisualTreeHelper.GetParent(root);
while (current != null)
{
yield return current;
current = VisualTreeHelper.GetParent(current);
}
}
}
With this available the ListBox (and all other UIElements for that matter) gets a couple of new extension methods Descendents and Ancestors. We can combine those with Linq to search for stuff. In this case you could use:-
ScrollViewer sv = SomeListBox.Descendents().OfType<ScrollViewer>().FirstOrDefault();
Does anybody have a good way of finding ALL the controls within an object that is of the same type? Here's my scenario, I have a tab control and within each tab control exists a user control (ALL of which match the same base type e.g. MyBaseClassControl). I want to be able to find that user control WITHOUT having to use the control.FindName("controlName") method, rather I would like to get a handle on the control by type (e.g. base class). The VisualTreeHelper class seems to do nothing for me as it only returns native Silverlight objects.
Given this:
public static IEnumerable<DependencyObject> AllChildren(this DependencyObject root)
{
var children = root.DirectChildren().ToList();
return children.Union(children.SelectMany(o => o.AllChildren()));
}
public static IEnumerable<DependencyObject> DirectChildren(this DependencyObject parent)
{
var childCount = VisualTreeHelper.GetChildrenCount(parent);
for (var i = 0; i < childCount; i++)
yield return System.Windows.Media.VisualTreeHelper.GetChild(parent, i);
}
You could do this:
myObj.AllChildren().OfType<MyBaseClassControl>();
I want to add a simple (at least I thought it was) behaviour to my WPF TextBox.
When the user presses Escape I want the TextBox he is editing to have the text it had when the user started editing, AND I want to remove the focus from the TextBox.
I don't have any problem setting the text for the value it had in the beginning of the edit.
The problem is to remove the focus of the element. I don't want to move the focus to any other component, I just want the TextBox to lose focus. Will I have to have an invisible element to set the focus so my TextBox can lose focus?
in .NET Framework 4 just Keyboard.ClearFocus();
The code I have been using :
// Move to a parent that can take focus
FrameworkElement parent = (FrameworkElement)textBox.Parent;
while (parent != null && parent is IInputElement && !((IInputElement)parent).Focusable)
{
parent = (FrameworkElement)parent.Parent;
}
DependencyObject scope = FocusManager.GetFocusScope(textBox);
FocusManager.SetFocusedElement(scope, parent as IInputElement);
Since none of the above answers worked for me and the accepted answer does work only for a keyboard focus, I came to the following approach:
// Kill logical focus
FocusManager.SetFocusedElement(FocusManager.GetFocusScope(textBox), null);
// Kill keyboard focus
Keyboard.ClearFocus();
Kills both, logical as well as the keyboard focus.
A bit late to the party, but it was helpful to me so here it goes.
Since .Net 3.0, FrameworkElement has a MoveFocus function which did the trick for me.
You can set the focus to a focusable ancestor. This code will work even if the textbox is inside a template with no focusable ancestors inside that same template:
DependencyObject ancestor = textbox.Parent;
while (ancestor != null)
{
var element = ancestor as UIElement;
if (element != null && element.Focusable)
{
element.Focus();
break;
}
ancestor = VisualTreeHelper.GetParent(ancestor);
}
AFAIK, it is not possible to completely remove the focus. Something in your Window will always have the focus.
For me, it's quite tricky, especially when using with LostFocus binding.
However, my workaround is to add an empty label and focus on it.
<Label Name="ResetFocusArea" Focusable="True" FocusVisualStyle="{x:Null}" />
...
OnKeyDown(object sender, RoutedEventArgs e)
{
//if is Esc
ResetFocusArea.Focus();
}
Using LPL's answer worked for me, but it would also make me unable to select any options in dropdown menues. To combat this, I added a check to see if the focused element was a textbox.
Doing the same check for when pressing enter, my final code looked like this:
public Menu()
{
InitializeComponent();
this.PreviewMouseDown += PreviewMouseDownEventHandler;
this.KeyDown += WindowKeyDownHandler;
}
void ClearFocus()
{
UIElement elementWithFocus = Keyboard.FocusedElement as UIElement;
if (elementWithFocus is System.Windows.Controls.TextBox tb)
{
if (Keyboard.FocusedElement != null)
{
Keyboard.FocusedElement.RaiseEvent(new RoutedEventArgs(UIElement.LostFocusEvent));
Keyboard.ClearFocus();
}
}
}
private void PreviewMouseDownEventHandler(object sender, MouseButtonEventArgs e)
{
ClearFocus();
}
private void WindowKeyDownHandler(object sender, System.Windows.Input.KeyEventArgs e)
{
if (e.Key == Key.Enter)
{
ClearFocus();
}
}
With this, I didn't need to add a focuslost to every textbox, and it can easily extend to other elements without breaking compatability with other parts of the program.
In Windows Phone Development, I just did Focus() or this.Focus() in the PhoneApplicationPage and it worked like a charm.
My answer does not adress the above question directly, however, I feel that the wording of it has caused it to become "The Question" about programmatically getting rid of focus. A common scenario where this is needed is for the user to be able to clear focus upon left-clicking the background of a root control, like window.
So, to achieve this, you can create an Attached Behavior that will switch focus to a dynamically created control (in my case, an empty label). It is preferrable to use this behavior on the highest-level elements like windows, as it iterates through it's children to find a panel it can add a dummy label to.
public class LoseFocusOnLeftClick : Behavior<FrameworkElement>
{
private readonly MouseBinding _leftClick;
private readonly Label _emptyControl = new Label() { Focusable = true, HorizontalAlignment = HorizontalAlignment.Left, VerticalAlignment = VerticalAlignment.Top };
public LoseFocusOnLeftClick()
{
_leftClick = new MouseBinding(new RelayCommand(LoseFocus), new MouseGesture(MouseAction.LeftClick));
}
protected override void OnAttached()
{
AssociatedObject.InputBindings.Add(_leftClick);
AssociatedObject.Loaded += AssociatedObject_Loaded;
}
protected override void OnDetaching()
{
AssociatedObject.InputBindings.Remove(_leftClick);
AssociatedObject.Loaded -= AssociatedObject_Loaded;
}
private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
{
AssociatedObject.Loaded -= AssociatedObject_Loaded;
AttachEmptyControl();
}
private void AttachEmptyControl()
{
DependencyObject currentElement = AssociatedObject;
while (!(currentElement is Panel))
{
currentElement = VisualTreeHelper.GetChild(currentElement, 0);
}
((Panel)currentElement).Children.Add(_emptyControl);
}
private void LoseFocus()
{
_emptyControl.Focus();
}
}
If you want to remove focus from a certain TextBox, just add this line..
textBox.Focusable = false;