WPF : Binding cannot find source - wpf

I try to make my own ContentControl that derives from Control to fully understand dark wpf tree concepts. For now, i just implemented the logical part (Content) of the ContentControl.
My code behind :
[ContentProperty("Content")]
public class MyContentControl : Control
{
public MyContentControl()
{
}
public Object Content
{
get { return (Object)GetValue(ContentProperty); }
set { SetValue(ContentProperty, value); }
}
public static readonly DependencyProperty ContentProperty =
DependencyProperty.Register("Content", typeof(Object), typeof(MyContentControl), new UIPropertyMetadata());
}
XAML :
<StackPanel x:Name="stackPanel">
<TextBlock Visibility="Collapsed" x:Name="textBlock" Text="Hello World"/>
<ContentControl>
<TextBlock Background="LightBlue" Text="{Binding Text, ElementName=textBlock}"/>
</ContentControl>
<local:MyContentControl>
<TextBlock Text="{Binding Text, ElementName=textBlock}"/>
</local:MyContentControl>
</StackPanel>
I got the following binding error :
System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=textBlock'. BindingExpression:Path=Text; DataItem=null; target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String')
It is like the inner TextBlock can't go up in the logical tree and find the original textblock on which it should bind. I wasn't able to set myContentControl as the parent of the Content object.
Any idee?
Thanks for your time.
Jonas

Relevant question: Binding ElementName. Does it use Visual Tree or Logical Tree
The binding you want is not possible because the same instance of MyContentControl could theoretically be used somewhere else in the application where the element "textBlock" is not in the scope.
If you want to do this type of binding you could use a Resource instead:
xmlns:clr="clr-namespace:System;assembly=mscorlib"
<StackPanel>
<StackPanel.Resources>
<clr:String x:Key="MyText">Hanky Panky</clr:String>
</StackPanel.Resources>
<TextBlock Text="{StaticResource MyText}" />
<ContentControl>
<TextBlock Text="{Binding Source={StaticResource MyText}}" />
</ContentControl>
</StackPanel>

I Just had to apply FrameworkElement.AddLogicalChild and FrameworkElement.RemoveLogicalChild when the ContentChanged and the binding is correctly apply (Verified with WPF Inspector).
So all this is about LogicalTree (and maybe the xaml namescope is inherited from logical parent). The TextBlock inside MyContentControl get the MyContentControl as Parent when MyContentControl.AddLogicalChild(TextBlock) is called.
My Code :
[ContentProperty("Content")]
public class MyContentControl : Control
{
public MyContentControl()
{
Content = new UIElementCollection(this, this);
}
public Object Content
{
get { return (Object)GetValue(ContentProperty); }
set { SetValue(ContentProperty, value); }
}
public static readonly DependencyProperty ContentProperty =
DependencyProperty.Register("Content", typeof(Object), typeof(MyContentControl), new UIPropertyMetadata(new PropertyChangedCallback(OnContentChanged)));
public static void OnContentChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
MyContentControl c = (MyContentControl)d;
if (e.OldValue != null)
{
c.RemoveLogicalChild(e.OldValue);
}
c.AddLogicalChild(e.NewValue);
}
protected override System.Collections.IEnumerator LogicalChildren
{
get
{
List<Object> l = new List<object>();
if (Content != null)
l.Add(Content);
return l.GetEnumerator();
}
}
}

Related

Can't bind DependencyProperties from UserControl code behind to ViewModel

I'm trying to create a UserControl in my WPF project which I want should have a DependencyProperty that I can bind to in the parent. The project is written as MVVM and I'm using Caliburn micro.
I really want to write clean and maintainable code using MVVM, so I want my UserControls to utilize viewmodels as much as possible and code behind as little as possible.
The problem is that I'm unsuccessful in getting the binding between the parent and the UserControl viewmodel to work correctly.
MyUserControl:
public partial class MyUserControlView : UserControl
{
public MyUserControlView()
{
InitializeComponent();
// If no Datacontext is set, binding between parent property and textbox text works - one way only (set from parent)!.
// -
// If Datacontext is set to this, bindings with properties in MyUserControlView code behind works.
//DataContext = this;
// If Datacontext is set to MyUserControlViewModel, binding between MyUserControlViewModel and MyUserControlView works, but not with parent.
DataContext = new MyUserControlViewModel();
}
public string ProjectNumber
{
get { return (string)GetValue(MyUserControlValueProperty); }
set { SetValue(MyUserControlValueProperty, value); }
}
public static readonly DependencyProperty MyUserControlValueProperty =
DependencyProperty.Register("ProjectNumber", typeof(string), typeof(MyUserControlView), new PropertyMetadata(null, new PropertyChangedCallback(OnProjectNumberUpdate)));
private static void OnProjectNumberUpdate(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var view = d as MyUserControlView;
view.ProjectNumberText.Text = e.NewValue as string;
}
}
MyUserControl code behind:
<StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="In MyUserControl: " />
<TextBlock Text="{Binding ProjectNumber}" />
</StackPanel>
<TextBox Name="ProjectNumberText" Text="{Binding ProjectNumber, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" />
</StackPanel>
MyUserControl ViewModel:
public class MyUserControlViewModel : Screen
{
private string _projectNumber;
public string ProjectNumber
{
get { return _projectNumber; }
set
{
_projectNumber = value;
NotifyOfPropertyChange(() => ProjectNumber);
}
}
}
Parent view:
<StackPanel>
<local:MyUserControlView ProjectNumber="{Binding ParentProjectNumber}" />
<StackPanel Orientation="Horizontal">
<TextBlock Text="In parent: "/>
<TextBlock Text="{Binding ParentProjectNumber}" />
</StackPanel>
</StackPanel>
Parent ViewModel:
public class ShellViewModel : Screen
{
public ShellViewModel()
{
ParentProjectNumber = "Hello from parent!";
}
private string _parentProjectNumber;
public string ParentProjectNumber
{
get { return _parentProjectNumber; }
set
{
_parentProjectNumber = value;
NotifyOfPropertyChange(() => ParentProjectNumber);
}
}
}
I know I'm probably way off here, but I have no idea what to do to get the bindings to work correctly.
Is there a better way to bind between a DependencyProperty and a viewmodel? Can I put the DP in the viewmodel somehow?
Here is the entire project solution: https://github.com/ottosson/DependencyPropertyTest
don't change UserControl.DataContext from inside UserControl. it can and will create issues later.
use proper name for DP (ProjectNumberProperty and corresponding ProjectNumber) and add BindsTwoWayByDefault to metadata:
public partial class MyUserControlView : UserControl
{
public MyUserControlView()
{
InitializeComponent();
}
public string ProjectNumber
{
get { return (string)GetValue(ProjectNumberProperty); }
set { SetValue(ProjectNumberProperty, value); }
}
public static readonly DependencyProperty ProjectNumberProperty = DependencyProperty.Register
(
"ProjectNumber",
typeof(string),
typeof(MyUserControlView),
new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault)
);
}
fix bindings in xaml:
<StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="In MyUserControl: " />
<TextBlock Text="{Binding Path=ProjectNumber, RelativeSource={RelativeSource AncestorType=UserControl}}" />
</StackPanel>
<TextBox Text="{Binding Path=ProjectNumber, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay, RelativeSource={RelativeSource AncestorType=UserControl}}" />
</StackPanel>
that should do it.
btw, "clean and maintainable code using MVVM" and "want my UserControls to utilize viewmodels as much as possible" sort of contradict each other.
also nothing wrong with code-behind in UserControls as long as that code handles only view functionality. for example: DataGrid source code contains 8000+ LoC

How to expose internal control's property to its parent UserControl in WPF

I have a DialogPrompt UserControl that will have an Image and a TextBlock. Here is the template:
<UserControl>
<Button x:Name="_OkButton" Content="OK"/>
<DockPanel >
<Image/>
<TextBlock x:Name="_DialogTextBox" />
</DockPanel>
</UserControl>
How do I expose Source property of the Image and Text property of the TextBlock inside my UserControl?
I would create two DependencyProperties, one for the Text and one for the Image Source.
The Image Source DependencyProperty will automatically set the inner Image control's source whenever it is updated. Similarly, the Text DependencyProperty will be setting the Text of the inner TextBlock control as well.
Here is the setup:
public partial class MyUserControl : UserControl
{
#region ImageSource
public static readonly DependencyProperty ImageSourceProperty =
DependencyProperty.Register
(
"ImageSource",
typeof(Uri),
typeof(MyUserControl),
new FrameworkPropertyMetadata(new PropertyChangedCallback(OnImageSourceChanged))
);
public Uri ImageSource
{
get { return (Uri)GetValue(ImageSourceProperty); }
set { SetValue(ImageSourceProperty, value); }
}
#endregion ImageSource
#region Text
public static readonly DependencyProperty TextProperty =
DependencyProperty.Register
(
"Text",
typeof(string),
typeof(MyUserControl),
new FrameworkPropertyMetadata("")
);
public string Text
{
get { return (string)GetValue(TextProperty); }
set { SetValue(TextProperty, value); }
}
#endregion Text
public MyUserControl()
{
InitializeComponent();
}
private static void OnImageSourceChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
var myUserControl = sender as MyUserControl;
if (myUserControl != null)
{
myUserControl.ImageSource.Source = new BitmapImage((Uri) e.NewValue);
}
}
}
Whenever the Image Source changes, this will automatically update the source of the inner Image control. Note, we need to do some conversion here since the Image control itself uses an ImageSource type.
XAML can then be updated to:
<UserControl x:Name="ControlName">
<Button x:Name = "OkButton" Content="OK"/>
<DockPanel >
<Image x:Name = "MyImage" />
<TextBlock x:Name = "DialogTextBox" Text="{Binding ElementName=ControlName, Path=Text}"/>
</DockPanel>
</UserControl>
Here, the inner TextBlock control simply binds to the Text DependencyProperty of the parent (the main UserControl).
In your code behind, add 2 DependencyProperties and bind them to your Image Source and to your TextBlock Text.
Here is a tutorial on how to use and create Dependency Properties :
http://www.wpftutorial.net/dependencyproperties.html
For your binding in your xaml, here is an example :
<Image Source="{Binding YourProperty, RelativeSource={RelativeSource FindAncestor, AncestorType=YourUserControl}}/>

Property bound to DependencyProperty won't update despite TwoWay Binding set

I have a little problem here. I've created custom TreeView using RadTreeView. It all works nice, but I've encountered an obstacle. I've set DependencyProperty for SelectedItem in TreeView. I nest my control in View, bind property to SelectedItem in TwoWay mode, but bound property won't update, it's null all the time, despite DependencyProperty value being set.
Here's tree xaml:
<Grid xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'
xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
xmlns:sdk='http://schemas.microsoft.com/winfx/2006/xaml/presentation/sdk'
xmlns:telerik='http://schemas.telerik.com/2008/xaml/presentation' x:Name='this' >
<Grid.Resources>
<DataTemplate x:Key='ChildTemplate'>
<TextBlock Text='{Binding Path=ChildPath}' Margin='5,0' />
</DataTemplate>
<telerik:HierarchicalDataTemplate x:Key='NameTemplate' ItemsSource='{Binding ChildrenCollectionPath}' ItemTemplate='{StaticResource ChildTemplate}'>
<TextBlock Text='{Binding Path=ParentPath }' Padding='7'/>
</telerik:HierarchicalDataTemplate>
</Grid.Resources>
<telerik:RadTreeView x:Name='rtvTreeView' Padding='5' BorderThickness='0' IsEditable='False' IsLineEnabled='True' IsExpandOnDblClickEnabled='False' ItemTemplate='{StaticResource NameTemplate}' />
</Grid>
Below is way I nest the control in View:
<windows:TreeViewReuse CollectionSource="{Binding SitesCollectionWithAddress}" ParentPath="Napis" Grid.Column="0" BorderThickness="2" SelectedItemD="{Binding SelectedSide, ElementName=this, UpdateSourceTrigger=Explicit, Mode=TwoWay}" ChildPath="FullAddress" ChildrenCollectionPath="AdresyStrony" BorderBrush="Red" DoubleClickCommand="{Binding TreeViewDoubleClick}">
</windows:TreeViewReuse>
And here's Tree's code behind in parts:
public partial class TreeViewReuse : UserControl
{
static Telerik.Windows.FrameworkPropertyMetadata propertyMetaData = new Telerik.Windows.FrameworkPropertyMetadata(null,
Telerik.Windows.FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, new PropertyChangedCallback(SelectedItemChangedCallback));
public object SelectedItemD
{
get { return GetValue(SelectedItemDProperty); }
set { SetValue(SelectedItemDProperty, value); }
}
public static readonly DependencyProperty SelectedItemDProperty =
DependencyProperty.Register("SelectedItemD", typeof(object), typeof(TreeViewReuse), propertyMetaData);
public TreeViewReuse()
{
InitializeComponent();
Loaded += new RoutedEventHandler(TreeViewReuse_Loaded);
}
void treeView_SelectionChanged(object sender, Telerik.Windows.Controls.SelectionChangedEventArgs e)
{
SelectedItemD = _treeView.SelectedItem;
}
static private void SelectedItemChangedCallback(DependencyObject dp, DependencyPropertyChangedEventArgs e)
{
}
Does anyone have an idea why property bound to SelectedItemD does not update? I don't care about setting tree's selected item from it, I only want to set it to selected item.
Here's property:
public StronaSprawy SelectedSide
{
get
{
return _selectedSide;
}
set
{
_selectedSide = value;
}
}
Your Dependency Property looks fine.. all except for that Telerik.Windows.FrameworkPropertyMetadata instance.
Silverlight does not support setting meta data options, so I cant think how the Telerik implementation will achieve that. It is possible that Telerik have their own DP implementation, or even that this type of property meta data only works with their controls.
Try using the standard System.Windows.PropertyMetaData type instead and see if that works for you.

Binding to user control's collection property items in xaml

I have created a user control with collection property:
public static readonly DependencyProperty
MyListProperty = DependencyProperty.Register(
"MyList",
typeof(ObservableCollection<Test>),
typeof(UserControl1),
new FrameworkPropertyMetadata(new ObservableCollection<Test>())
);
public ObservableCollection<Test> MyList
{
get { return (ObservableCollection<Test>)base.GetValue(MyListProperty); }
set { base.SetValue(MyListProperty, value); }
}
public static readonly DependencyProperty
BProperty = DependencyProperty.Register(
"B",
typeof(string),
typeof(UserControl1),
new FrameworkPropertyMetadata(null)
);
public string B
{
get { return (string)base.GetValue(BProperty); }
set { base.SetValue(BProperty, value); }
}
The Test class is:
public class Test : DependencyObject
{
public static readonly DependencyProperty
AProperty = DependencyProperty.Register(
"A",
typeof(string),
typeof(Test),
new FrameworkPropertyMetadata(null)
);
public string A
{
get { return (string)base.GetValue(AProperty); }
set { base.SetValue(AProperty, value); }
}
}
Then, i'm trying to use my control for binding:
<TextBox x:Name="tb1" Text="def"/>
<my:UserControl1 x:Name="uc1" B="{Binding ElementName=tb1, Path=Text}">
<my:UserControl1.MyList>
<my:Test A="{Binding ElementName=tb1, Path=Text}"></my:Test>
<my:Test A="100"></my:Test>
</my:UserControl1.MyList>
</my:UserControl1>
The first binding (with B property of User Control) works correctly. The problem is with second binding (with A property of Test which is MyList element). When debugging i have two items in MyList but the A property of the first one is null. Please tell me what I am missing here?
The problem here is, that the Binding to ElementName=tb1 can not be resolved, even it will never be evaluated. A Binding to an ElementName is resolved for DependencyObjects which are in the visual or logical Tree of a WPF Application. Adding items to your ObservableCollection (MyList) only means adding the items to the Collection, but not into the Visual Tree.
Edit:
Here is the approach discussed in the comments:
In your Window/Page:
<Window.Resources>
<!-- Declare the ViewModel as Resource -->
<my:ViewModel x:Key="viewModel">
<my:ViewModel.MyList>
<my:Test A="Hello sweet" />
<my:Test A="ViewModel" />
</my:ViewModel.MyList>
</my:ViewModel>
</Window.Resources>
<!-- Assign Ressource as DataContext -->
<StackPanel DataContext="{StaticResource viewModel}">
<TextBox x:Name="tb1" Text="def"/>
<!-- Reference your list within the ViewModel -->
<ListBox ItemsSource="{Binding Path=MyList}">
<ListBox.ItemTemplate>
<DataTemplate>
<!-- Bind your property -->
<TextBlock Text="{Binding Path=A}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</StackPanel>
And the implementation of ViewModel:
public class ViewModel
{
public ViewModel()
{
this.MyList = new ObservableCollection<Test>();
}
public ObservableCollection<Test> MyList { get; set; }
}
Of course, class Test no longer needs to implement a DependencyObject. Simple get/set Properties are okay.

Why WPF uses control's view model when binding value to the control?

I'm writing a value input control can be used everywhere. The control itself has a view model which set to its DataContext as usual. But when I use the control in a parent control like:
<UserControl x:Class="X.Y.Z.ParentControl">
...
<local:ValueInput Value="{Binding Path=MyValue}" />
...
</UserControl>
I'm going to bind the MyValue property of ParentControl's DataContext to the ValueInput control, but WPF tell me it cannot find the MyValue property in ValueInputViewModel class, which is the view model of ValueInput control itself. Why WPF is looking for the value from child's DataContext?
I just want to write a control which can be used like this:
<telerik:RadNumericUpDown Value="{Binding Path=NumberValue}" />
The NumberValue property is defined in in the parent's DataContext, not in the control's. This pattern works for teleriks control but not for my control.
What should I do?
For any FrameworkElement, there can be only 1 DataContext.
If UserControl has its own DataContext, it cannot use parent's DataContext.
However you can walk up to parent and get its DataContext (each time you need to reference Parent's DataContext) using RelativeSource
Binding="{Binding RelativeSource={RelativeSource FindAncestor,
AncestorType={x:Type Window}}, Path=DataContext.NumberValue}"
For this example to work, Parent (root at any level) should be Window. If it is a UserControl,
Binding="{Binding RelativeSource={RelativeSource FindAncestor,
AncestorType={x:Type UserControl}}, Path=DataContext.NumberValue}"
The code is from this link provided by fiq
My friend told me not to use DataContext as the view model in a standalone control since DataContext would be easily overridden - define a ViewModel property and bind in the XAML could solve the problem. Here's an example:
View model class:
public class MyValueInputViewModel
{
public string MyText { get; set; }
}
Code behind:
public partial class MyValueInput : UserControl
{
public MyValueInput()
{
InitializeComponent();
this.ViewModel = new MyValueInputViewModel
{
MyText = "Default Text"
};
}
public static readonly DependencyProperty ViewModelProperty =
DependencyProperty.Register("ViewModel", typeof(MyValueInputViewModel), typeof(MyValueInput));
public MyValueInputViewModel ViewModel
{
get
{
return (MyValueInputViewModel)this.GetValue(ViewModelProperty);
}
private set
{
this.SetValue(ViewModelProperty, value);
}
}
public static readonly DependencyProperty ValueProperty =
DependencyProperty.Register("Value", typeof(string), typeof(MyValueInput), new PropertyMetadata(OnValuePropertyChanged));
private static void OnValuePropertyChanged(DependencyObject o, DependencyPropertyChangedEventArgs args)
{
var input = (MyValueInput)o;
input.ViewModel.MyText = input.Value;
}
public string Value
{
get { return (string)this.GetValue(ValueProperty); }
set { this.SetValue(ValueProperty, value); }
}
}
XAML:
<UserControl x:Class="..." x:Name="Self" ...>
<Grid>
<TextBox Text="{Binding ViewModel.MyText, ElementName=Self, UpdateSourceTrigger=PropertyChanged}" />
</Grid>
</UserControl>

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