Why are Silverlight ContentControls not garbage collected? - silverlight

I've been investigating why some of my controls aren't being garbage collected and noticed it's easy to prevent simple controls that inherit from ContentControl from ever being destroyed. Here's an example:
Here is my custom ContentControl:
public class MyCustomControl : ContentControl
{
public MyCustomControl()
{
Debug.WriteLine("Constructed");
}
~MyCustomControl()
{
Debug.WriteLine("Destroyed");
}
}
Now if I put it on a page like so:
<navigation:Page x:Class="SimpleTestBed.Views.CustomControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
xmlns:navigation="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Navigation"
xmlns:local="clr-namespace:SimpleTestBed"
d:DesignWidth="640" d:DesignHeight="480"
Title="CustomControl Page">
<Grid x:Name="LayoutRoot">
<StackPanel>
<local:MyCustomControl>
<TextBox Text="{Binding SomeProperty,Mode=TwoWay}"></TextBox>
</local:MyCustomControl>
</StackPanel>
</Grid>
With the following code behind:
public partial class CustomControl : Page
{
public CustomControl()
{
InitializeComponent();
this.DataContext = new CustomControlViewModel();
this.Unloaded += new RoutedEventHandler(OnUnloaded);
}
void OnUnloaded(object sender, RoutedEventArgs e)
{
this.DataContext = null;
}
// Executes when the user navigates to this page.
protected override void OnNavigatedTo(NavigationEventArgs e)
{
}
}
Then the view model is:
public class CustomControlViewModel : INotifyPropertyChanged
{
#region INotifyPropertyChanged
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
RaisePropertyChanged(propertyName);
}
private void RaisePropertyChanged(string propertyName)
{
if (PropertyChanged != null)
PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
}
#endregion
private string _someProperty = "Initial Value";
public string SomeProperty
{
get { return _someProperty; }
set
{
if (_someProperty != value)
{
string oldValue = _someProperty;
_someProperty = value;
OnPropertyChanged("SomeProperty");
OnSomePropertyChanged(oldValue, value);
}
}
}
protected virtual void OnSomePropertyChanged(string oldValue, string newValue)
{
}
}
Now when I navigate away from this page and try garbage collecting with GC.Collect(), as long if I've made no changes to the text in the Textbox, the ContentControl and Page are destroyed as expected by the GC. But if I've edited some text and navigated away from the page and then tried to GC.Collect(), the ContentControl doesn't get garbage collected.
Can anyone explain this behavior?
Actually, you can force the GC to collect the control by 'flickering' the Template of the control when you unload:
void MyCustomControl_Unloaded(object sender, RoutedEventArgs e)
{
Debug.WriteLine("MyCustomControl Unloaded");
ControlTemplate oldTemplate = this.Template;
this.Template = null;
this.Template = oldTemplate;
}
I presume this destroys the current visual tree losing references of the tree's first component to its parent (the custom control). It certainly forces the control to recall OnApplyTemplate when the control is reloaded.
Is this the correct pattern for developing Silverlight controls without leaking? If so, it strikes me as a bit bizarre that the template isn't disposed automatically when the control unloads.
A good account of this behavior would be much appreciated as it goes right to the heart of the life-cycle of Silverlight controls.

My experience showed that memory leaks in Silverlight are coused by top 2 reason :
Events => Make sure that you remove attached events once when it is not needed or in class destructor.
Templates => Solution define templates in Resource section

Related

Data binding doesn't work on Custom controls inside collection

WPF Data binding doesnt work for custom controls that are defined inside a xaml collection tag. I just want to define a collection of custom widgets inside a custom control and bind some widgets properties against viewmodel properties. Like so.
<Window x:Class="WpfApp1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfApp1"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800">
<Window.DataContext>
<local:MainViewModel/>
</Window.DataContext>
<Grid>
<local:MyCustomControl>
<local:MyCustomControl.Widgets>
<local:MyCustomWidget ImportantToggle="{Binding SomeToggle}"/>
</local:MyCustomControl.Widgets>
</local:MyCustomControl>
</Grid>
</Window>
That is my custom control. I use an obseravblecollection for the widgets and call SetValue in the constructor to get propertychanged callback later (right now not used in example)
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Windows;
namespace WpfApp1
{
public class MyCustomControl : FrameworkElement
{
public ObservableCollection<MyCustomWidget> Widgets
{
get { return (ObservableCollection<MyCustomWidget>)this.GetValue(WidgetsProperty); }
set { this.SetValue(WidgetsProperty, value); }
}
public static DependencyProperty WidgetsProperty = DependencyProperty.Register("Widgets", typeof(ObservableCollection<MyCustomWidget>), typeof(MyCustomControl), new PropertyMetadata(null, (e, args) => ((MyCustomControl)e).WidgetsChanged(args)));
public void WidgetsChanged(DependencyPropertyChangedEventArgs e)
{
Debug.WriteLine("widgets collection object changed inside my custom control!");
}
public MyCustomControl()
{
this.SetValue(WidgetsProperty, new ObservableCollection<MyCustomWidget>());
}
}
}
and that is my custom widget:
namespace WpfApp1
{
public class MyCustomWidget : FrameworkContentElement
{
public bool ImportantToggle
{
get { return (bool)this.GetValue(ImportantToggleProperty); }
set { this.SetValue(ImportantToggleProperty, value); }
}
public static DependencyProperty ImportantToggleProperty = DependencyProperty.Register("ImportantToggle", typeof(bool), typeof(MyCustomWidget), new PropertyMetadata(false, (e, args) => ((MyCustomWidget)e).ImportantToggleChanged(args)));
public void ImportantToggleChanged(DependencyPropertyChangedEventArgs e)
{
Debug.WriteLine("my toggle changed inside my custom widget!");
}
}
}
And finally my simplistic ViewModel:
using System;
using System.ComponentModel;
using System.Runtime.CompilerServices;
namespace WpfApp1
{
public class MainViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
private bool _someToggle;
public bool SomeToggle
{
get { return this._someToggle; }
set
{
this._someToggle = value;
this.NotifyPropertyChanged();
}
}
public MainViewModel()
{
this.SomeToggle = !this.SomeToggle;
}
}
}
Thats the output I get from Debug.Writeline: widgets collection object changed inside my custom control!
Observation: I cant bind against properties of MyCustomWidget. I understand that the binding might fail in this scenario because the observablecollection is created inside of the constructor of mycustomcontrol, but I dont know how to fix it to get the binding working inside mycustomwidget.
For that binding to work, your local:MyCustomWidget needs to have the same DataContext as the main window. WPF elements inherit their logical parent's DataContext. MyCustomWidget doesn't, because it's not in the logical tree. It's just sitting there. You're not adding it to any kind of normal child collection of its parent, just to a random ObservableCollection that the framework doesn't know about.
The code below is probably a crude hack. I haven't investigated this corner of WPF. I urge you with the utmost sincerity to find out the right way of doing this. But with this addition to your code, I hit the propertychanged event in MyCustomWidget when the binding is initialized.
public MyCustomControl()
{
this.SetValue(WidgetsProperty, new ObservableCollection<MyCustomWidget>());
Widgets.CollectionChanged += Widgets_CollectionChanged;
}
private void Widgets_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.NewItems is System.Collections.IEnumerable)
{
foreach (MyCustomWidget widget in e.NewItems)
{
AddLogicalChild(widget);
}
}
}
By the way, you can save the trouble of toggling the toggle in the MainViewModel constructor. That happens long before the binding exists. I added a checkbox instead:
<StackPanel>
<CheckBox IsChecked="{Binding SomeToggle}">Test Toggle</CheckBox>
<local:MyCustomControl>
<local:MyCustomControl.Widgets>
<local:MyCustomWidget
ImportantToggle="{Binding SomeToggle}"
/>
</local:MyCustomControl.Widgets>
</local:MyCustomControl>
</StackPanel>
Update:
This omits your Widgets collection entirely, and the binding works without any effort on our part. The child widgets will be in MyCustomControl.Children. Importantly that we aren't limiting the child type to MyCustomWidget any more. That's a significant design change, and may not fit your requirements. You could examine the Panel class closely, and write a class that works the same way, but accepts only one type of child (that would mean writing an analog of UIElementCollection, which will be mostly a big pile of tedious boilerplate).
MyCustomControl.cs
[ContentProperty("Children")]
public class MyCustomControl : Panel
{
}
MyCustomWidget.cs
public class MyCustomWidget : Control
{
public bool ImportantToggle
{
get { return (bool)this.GetValue(ImportantToggleProperty); }
set { this.SetValue(ImportantToggleProperty, value); }
}
public static DependencyProperty ImportantToggleProperty =
DependencyProperty.Register("ImportantToggle", typeof(bool), typeof(MyCustomWidget),
new PropertyMetadata(false, (e, args) => ((MyCustomWidget)e).ImportantToggleChanged(args)));
public void ImportantToggleChanged(DependencyPropertyChangedEventArgs e)
{
Debug.WriteLine("my toggle changed inside my custom widget!");
}
}
MainWindow.xaml
<local:MyCustomControl>
<local:MyCustomWidget
ImportantToggle="{Binding SomeToggle}"
/>
</local:MyCustomControl>

How to use to use UserControl DP and MVVM

I haven`t found answer for this question in internet.
Is there some way to use in UserControl DP and MVVM together?
For example, I created UserControl, and i need to display some text on it. My UserControl has DP which takes some data (f.e. string) from consumer.
I have some code behind:
public partial class MyUserControl : UserControl
{
public MyUserControl()
{
InitializeComponent();
}
***
public string Text
{
get { return (PointCollection)GetValue(TextProperty); }
set { SetValue(TextProperty, value); }
}
public static readonly DependencyProperty TextProperty =
DependencyProperty.Register(nameof(Text),
typeof(string),
typeof(MyUserControl),
new FrameworkPropertyMetadata(null, new PropertyChangedCallback(TextChanged))
);
private static void TextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
((MyUserControl)d).DataContext.Txt = (string)e.NewValue;
}
***
}
Here is code of ViewModel class:
class MyUserControlViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
handler?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
private string _txt;
public MyUserControlViewModel(){}
***
public string Txt
{
get{return _txt;}
set
{
if(_txt!= value)
{
_txt= value;
OnPropertyChanged("Txt");
}
}
}
***
}
And here some XAML code of UserControl in which i want to bind text of TextBlock to property Txt of ViewModel, so:
<UserControl x:Class="SimpleWPFChartExample.ChartSurface"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:SimpleWPFChartExample"
mc:Ignorable="d">
<UserControl.DataContext>
<local:SimpleWPFChartExample />
</UserControl.DataContext>
<Grid>
<TextBlock Text="{Binding Path=Txt}"/>
</Grid>
</UserControl>
So, if I do this way I don`t see any changes of DP Text and any changes of Txt, when i put some data in DP Text in consumer application.
What should I do?
You didn't mention why you want to use both dependency properties and a viewmodel, but it's easy to get one working. You just need to use the viewmodel you want to use instead of a different one. This is the wrong viewmodel:
<UserControl.DataContext>
<local:SimpleWPFChartExample />
</UserControl.DataContext>
This is the right one:
<UserControl.DataContext>
<local:MyUserControlViewModel />
</UserControl.DataContext>
At least, that would appear to be the case based on your question. But you have a number of copy and paste errors in there: For example, your Text string property getter casts the return value from GetValue() to PointCollection; that won't even compile. Neither will this: ((MyUserControl)d).DataContext.Txt = (string)e.NewValue;
This will compile:
private static void TextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var ctl = ((MyUserControl)d);
var vm = (MyUserControlViewModel)ctl.DataContext;
vm.Txt = (String)e.NewValue;
}
So for all I know you really are using the correct viewmodel in your actual code, in which case the problem is in code you're not sharing here. It may be that the problem is in whatever you're doing to set Text.
It would help if you could provide a complete, minimal, single-property example that compiles, but and then fails at runtime to meet your expectations.

Can you have an event setter bound to an event of the data context?

Im trying to create something like this -
I have an observable collection of points. Each point has a position and a colour. When any points position or colour changes(they implement notification change), I want to "repaint" the background gradient. Currently I have an itemscontrol where I have the sliders bound to the points position and the gradient is initially drawn. Now, I want to know how I can call a function in the code behind of my view when the propertychanged event on a 'point' fires, so that I can repaint the gradient. Im wondering if an event setter can somehow be used?
Whilst I could do the propertychanged event subscribing in code behind, I'd like to do it in XAML?
PLease note : I specifically want to take this approach of manually repainting in code behind for other reasons, so if I could get answers to the specific problem above rather than alternative solutions please.
I guess you can create an attached property to subscribe to PropertyChanged events of the value of the DataContext property.
public static class Props
{
public static DependencyProperty OnPropertyChangedProperty = DependencyProperty.RegisterAttached(
"OnPropertyChanged", typeof(PropertyChangedEventHandler), typeof(Props),
new PropertyMetadata(OnPropertyChangedPropertyChanged));
public static PropertyChangedEventHandler GetOnPropertyChanged (DependencyObject d)
{
return (PropertyChangedEventHandler)d.GetValue(OnPropertyChangedProperty);
}
public static void SetOnPropertyChanged (DependencyObject d, PropertyChangedEventHandler value)
{
d.SetValue(OnPropertyChangedProperty, value);
}
private static void OnPropertyChangedPropertyChanged (DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var inpc = (INotifyPropertyChanged)((FrameworkElement)d).DataContext;
if (inpc == null)
throw new ArgumentException("DataContext of the framework element must not be null.");
var oldChanged = (PropertyChangedEventHandler)e.OldValue;
if (oldChanged != null)
inpc.PropertyChanged -= oldChanged;
var newChanged = (PropertyChangedEventHandler)e.NewValue;
if (newChanged != null)
inpc.PropertyChanged += newChanged;
}
}
Usage:
<Window x:Class="So17382721PropertyChangedXaml.MainWindow" x:Name="root"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:So17382721PropertyChangedXaml"
Title="MainWindow" Height="350" Width="525">
<Window.Resources>
<DataTemplate DataType="{x:Type local:Foo}">
<!-- Here, we subscribe to DataContext.PropertyChanged;
handler is defined in the MainWindow class -->
<Grid local:Props.OnPropertyChanged="{Binding FooPropertyChanged, ElementName=root}">
<TextBox Text="{Binding Bar, UpdateSourceTrigger=PropertyChanged}"/>
</Grid>
</DataTemplate>
</Window.Resources>
<Grid>
<ItemsControl ItemsSource="{Binding Foos, ElementName=root}"/>
</Grid>
</Window>
Code-behind:
using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Windows;
namespace So17382721PropertyChangedXaml
{
public partial class MainWindow
{
public ObservableCollection<Foo> Foos { get; private set; }
public MainWindow ()
{
Foos = new ObservableCollection<Foo> {
new Foo { Bar = "1" },
new Foo { Bar = "2" },
new Foo { Bar = "3" },
};
InitializeComponent();
}
private void OnFooPropertyChanged (object sender, PropertyChangedEventArgs e)
{
MessageBox.Show(this, string.Format("{0} of {1} changed.", e.PropertyName, sender));
}
// Subscribing to non-RoutedEvents in XAML is not straightforward, but we can define a property
public PropertyChangedEventHandler FooPropertyChanged
{
get { return OnFooPropertyChanged; }
}
}
public class Foo : INotifyPropertyChanged
{
private string _bar;
public string Bar
{
get { return _bar; }
set
{
_bar = value;
OnPropertyChanged();
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged ([CallerMemberName] string propertyName = null)
{
var handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}
Note: the attached property Props.OnPropertyChanged expects that DataContext is not changed during lifetime and is already specified. Handling DataContextChanged events is left as an exircize, if you need it.

Silverlight MVVM binding updates fire in undesired order

Scenario: In a Silverlight 4 MVVM project, we have a ListBox control containing items, the selected item is two-way-bound to the appropriate property in the ViewModel. Another control (for example reasons, I've stripped it down to a single TextBox) is data bound to the selected item's content. The value should update on leave/focus lost.
Problem: When the value in the TextBox is changed and we leave that TextBox by pressing the Tab key, everything works as desired - the value is updated. However, if the user clicks on a different item in the ListBox, then the SelectedItem setter is fired before the content of TextBox setter is fired, leaving no chance to handle the user input.
You can see in debugger, when adding breakpoints to the property setters, that the new ListView selection is applied first, before the TextBox update is processed.
Desired behavior: We need to know that the currently selected item was modified before the user has selected another item. It's not desired to have a custom update trigger which would notify on each key press (we know that's possible).
Can you help?
Code (a very simple example):
ViewModel
public abstract class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
var handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
public class ItemViewModel : ViewModelBase
{
private string _content;
public ItemViewModel(string initContent)
{
_content = initContent;
}
public string Content
{
get
{
return _content;
}
set
{
if (_content != value)
{
_content = value;
OnPropertyChanged("Content");
}
}
}
}
public class MainViewModel : ViewModelBase
{
private ObservableCollection<ItemViewModel> _items =
new ObservableCollection<ItemViewModel>();
private ItemViewModel _selectedViewModel;
public ObservableCollection<ItemViewModel> Items
{
get
{
return _items;
}
}
public ItemViewModel SelectedItem
{
get
{
return _selectedViewModel;
}
set
{
if (_selectedViewModel != value)
{
_selectedViewModel = value;
OnPropertyChanged("SelectedItem");
}
}
}
}
XAML
<Grid x:Name="LayoutRoot" Background="White">
<ListBox Height="100"
HorizontalAlignment="Left"
Margin="12,12,0,0"
VerticalAlignment="Top"
ItemsSource="{Binding Items}"
SelectedItem="{Binding SelectedItem, Mode=TwoWay}"
DisplayMemberPath="Content"
Width="220" />
<TextBox Height="23"
HorizontalAlignment="Left"
Margin="12,118,0,0"
Text="{Binding SelectedItem.Content, Mode=TwoWay}"
VerticalAlignment="Top"
Width="220" />
</Grid>
XAML Code Behind
public MvvmTestView()
{
InitializeComponent();
Loaded += new RoutedEventHandler(MvvmTestView_Loaded);
}
void MvvmTestView_Loaded(object sender, RoutedEventArgs e)
{
MainViewModel viewModel = new MainViewModel();
viewModel.Items.Add(new ItemViewModel("Hello StackOverflow"));
viewModel.Items.Add(new ItemViewModel("Thanks to Community"));
DataContext = viewModel;
}
UPDATE 1
I present a self designed solution for you to check out, which will be probably be the accepted one, I still want to encourage you to make comments and give your hints. Thanks.
You could add a behavior to your textbox to updated the binding every time the text is changed in the textbox. Maybe this solved your problems.
Here´s the code for the Behavior class:
public class UpdateTextBindingOnPropertyChanged : Behavior<TextBox> {
// Fields
private BindingExpression expression;
// Methods
protected override void OnAttached() {
base.OnAttached();
this.expression = base.AssociatedObject.GetBindingExpression(TextBox.TextProperty);
base.AssociatedObject.TextChanged+= OnTextChanged;
}
protected override void OnDetaching() {
base.OnDetaching();
base.AssociatedObject.TextChanged-= OnTextChanged;
this.expression = null;
}
private void OnTextChanged(object sender, EventArgs args) {
this.expression.UpdateSource();
}
}
Heres the XAML:
xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
xmlns:local="Namespace of the class where UpdateTextBindingOnPropertyChanged is defined"
<TextBox Text="{Binding SelectedItem.Content, Mode=TwoWay}">
<i:Interaction.Behaviors>
<local:UpdateTextBindingOnPropertyChanged />
</i:Interaction.Behaviors>
</TextBox >
This is one solution we currently came up with. It has the advantage that it separates different tasks to the appropriate layer. For example, the View enforces an update of the binding, while the ViewModel tells the View to do so. Another advantage is that its handled synchronously, which would for example allow to check the content right before switching away, and the call-stack remains unchanged without raising "External Code" (Going over Dispatcher or even DispatcherTimer would do so) which is better for maintenance and flow control. A disadvantage is the new Event which has to be bound and handled (and finally unbound. I present an anonymous handler only for example reasons).
How to get there?
In ViewModelBase, implement a new ForceBindingUpdate event:
public abstract class ViewModelBase : INotifyPropertyChanged
{
// ----- leave everything from original code ------
public event EventHandler ForceBindingUpdate;
protected void OnForceBindingUpdate()
{
var handler = ForceBindingUpdate;
if (handler != null)
handler(this, EventArgs.Empty);
}
}
In MainViewModel, update the setter of the SelectedItem property:
set // of SelectedItem Property
{
if (_selectedViewModel != value)
{
// Ensure Data Update - the new part
OnForceBindingUpdate();
// Old stuff
_selectedViewModel = value;
OnPropertyChanged("SelectedItem");
}
}
Update the MvvmTestView Code Behind to implement the new event:
void MvvmTestView_Loaded(object sender, RoutedEventArgs e)
{
// remains unchanged
Mvvm.MainViewModel viewModel = new Mvvm.MainViewModel();
viewModel.Items.Add(new Mvvm.ItemViewModel("Hello StackOverflow"));
viewModel.Items.Add(new Mvvm.ItemViewModel("Thanks to Community"));
// Ensure Data Update by rebinding the content property - the new part
viewModel.ForceBindingUpdate += (s, a) =>
{
var expr = ContentTextBox.GetBindingExpression(TextBox.TextProperty);
expr.UpdateSource();
};
// remains unchanged
DataContext = viewModel;
}
Last but not least, the minimal XAML Update: Give the TextBox a name by adding x:Name="ContentTextBox" Attribute to the TextBoxs XAML.
Done.
Actually, I don't know if this is the cleanest solution, but it gets close to what we had in mind.
Maybe you could handle TextBox LostFocus then (instead of listening to every key press)?
Other idea would be to keep a proxy property on the ViewModel instead of directly binding to SelectedItem.Content and writing some code to make sure the item is updated.
Solution №1
public class LazyTextBox: TextBox
{
//bind to that property instead..
public string LazyText
{
get { return (string)GetValue(LazyTextProperty); }
set { SetValue(LazyTextProperty, value); }
}
public static readonly DependencyProperty LazyTextProperty =
DependencyProperty.Register("LazyText", typeof(string), typeof(LazyTextBox),
new PropertyMetadata(null));
//call this method when it's really nessasary...
public void EnsureThatLazyTextEqualText()
{
if (this.Text != this.LazyText)
{
this.LazyText = this.Text;
}
}
}
Solution №2 (works as magic :) )
public class MainViewModel : ViewModelBase
{
private ObservableCollection<ItemViewModel> _items =
new ObservableCollection<ItemViewModel>();
private ItemViewModel _selectedViewModel;
public ObservableCollection<ItemViewModel> Items { get { return _items; } }
public ItemViewModel SelectedItem
{
get { return _selectedViewModel; }
set
{
if (_selectedViewModel != value)
{
if (SelectedItem != null)
{
SelectedItem.Content = SelectedItem.Content;
}
_selectedViewModel = value;
// A little delay make no harm :)
var t = new DispatcherTimer();
t.Interval = TimeSpan.FromSeconds(0.1);
t.Tick += new EventHandler(t_Tick);
t.Start();
}
}
}
void t_Tick(object sender, EventArgs e)
{
OnPropertyChanged("SelectedItem");
(sender as DispatcherTimer).Stop();
}
}
I know that in MVVM we do not want to put code in code behind. But in this instance it hurts nothing as it is entirely maintained in the UI and SOP is maintained.
By putting a ghost element to take focus we can swap the focus back in forth forcing
the text box to commit its contents. So in the code behind we take care of the focus wiggle.
But yet we still are using a relay command Update Command to execute the save. So the order is good as the Click event fires wiggling the view. And then the relay command UpdateCommand will fire and the textbox is committed and ready for update.
<MenuItem Header="_Save"
Command="{Binding UpdateCommand}" Click="MenuItem_Click">
</MenuItem>
private void MenuItem_Click(object sender, RoutedEventArgs e)
{
UIElement elem = Keyboard.FocusedElement as UIElement;
Keyboard.Focus(ghost);
Keyboard.Focus(elem);
}
Solution #3
public abstract class ViewModelBase : INotifyPropertyChanged
{
private List<string> _propNameList = new List<string>();
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
var handler = PropertyChanged;
if (handler != null)
_propNameList.Add(propertyName);
var t = new DispatcherTimer();
t.Interval = TimeSpan.FromSeconds(0);
t.Tick += new EventHandler(t_Tick);
t.Start();
}
void t_Tick(object sender, EventArgs e)
{
if (_propNameList.Count > 0)
{
var handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(_propNameList[0]));
_propNameList.Remove(_propNameList[0]);
}
}
}
PS: it's the same timer.. but this solution is more generic..

INotifyPropertyChanged not working on ObservableCollection property

I have a class called IssuesView which implements INotifyPropertyChanged. This class holds an ObservableCollection<Issue> and exposes it as a DependencyProperty called Issues for consumption by Bindings. It is defined as below -
public class IssuesView : DependencyObject, INotifyPropertyChanged
{
public Issues Issues
{
get { return (Issues)GetValue(IssuesProperty); }
set
{
SetValue(IssuesProperty, value);
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs("Issues"));
}
}
}
// Using a DependencyProperty as the backing store for Issues. This enables animation, styling, binding, etc...
public static readonly DependencyProperty IssuesProperty =
DependencyProperty.Register("Issues", typeof(Issues), typeof(IssuesView), new UIPropertyMetadata(null));
public IssuesView()
{
Refresh();
}
public void Refresh()
{
this.Issues = new Issues();
}
#region INotifyPropertyChanged Members
public event PropertyChangedEventHandler PropertyChanged;
#endregion
}
I have a test page declared like this -
<Page x:Class="Tracker.Pages.DEMO"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:cont="clr-namespace:Tracker.Controls"
Title="DEMO">
<StackPanel>
<Button Click="Button_Click">Change</Button>
<cont:IssueTimeline IssuesForTimeline="{Binding Source={StaticResource issuesView},Path = Issues}"/>
</StackPanel>
The IssuesView class is defined in Application.Resources.
Now in the event hadnler for the button i have this code -
private void Button_Click(object sender, RoutedEventArgs e)
{
IssuesView iv = Application.Current.FindResource("issuesView") as IssuesView;
if (!once)
{
foreach (Issue i in iv.Issues)
{
i.DormantFor = new TimeSpan(30, 0, 0, 0);
i.AssignedUserID = 12;
i.Name = "MyName";
i.Priority = Issue.Priorities.Critical;
i.Status = Issue.Statuses.New;
i.Summary = "NewSummary";
}
once = true;
}
else
{
iv.Refresh();
}
once is a simple boolean to test mutation of the collection versus repopulation.
The first button click alters the collection's items and the UI is updated properly since the items implement INotifyPropertyChanged but the second click repopulates the collection but does not update the UI even though the event is not null and fires properly.
Why does the UI not update on the second click? How can i make it so that repopulating the collection will cause a UI update?
You really need to simplify your repro. I can see several things wrong with it, but cannot help to solve your problem without seeing all of it. Here is my simple repro, which works just fine.
Window1.xaml:
<Window x:Name="_root" x:Class="CollectionRepro.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<StackPanel DataContext="{Binding ElementName=_root}">
<ItemsControl ItemsSource="{Binding Issues}"/>
<Button x:Name="_addButton">Add</Button>
<Button x:Name="_resetButton">Reset</Button>
</StackPanel>
</Window>
Window1.xaml.cs:
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Windows;
namespace CollectionRepro
{
public partial class Window1 : Window
{
public static readonly DependencyProperty IssuesProperty = DependencyProperty.Register("Issues",
typeof(ICollection<string>),
typeof(Window1));
public ICollection<string> Issues
{
get { return (ICollection<string>)GetValue(IssuesProperty); }
set { SetValue(IssuesProperty, value); }
}
public Window1()
{
InitializeComponent();
Reset();
_addButton.Click +=new RoutedEventHandler(_addButton_Click);
_resetButton.Click += new RoutedEventHandler(_resetButton_Click);
}
void _resetButton_Click(object sender, RoutedEventArgs e)
{
Reset();
}
void _addButton_Click(object sender, RoutedEventArgs e)
{
Issues.Add("Another issue");
}
private void Reset()
{
Issues = new ObservableCollection<string>();
}
}
}
First: there's no reason to implement INotifyProperty changed for DependencyProperties. DependencyProperties know when they change.
Second: I don't see an ObservableCollection in your code.
Third: it's not entirely clear to me (from the code you posted) where the issues you modify in the first click come from. I assume from another action, not posted here.
Am I correct if I assume that you want to clear the issues list with the second click (since I don't know what the Issues constructor does)?

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