I'm not too used to WPF, so this is probably something easy, but I've been struggling with it for a couple hours and can't seem to get how to properly do it.
Say I have a BaseUserControl descending from UserControl with a dependency property Text.
Then in XAML I'm creating a BaseUserControl descendant. I want that property Text to be bound to a control defined in that descendant. Say:
<base:BaseUserControl
... all namespaces ...
xmlns:base="clr-namespace:MyControlsBase"
x:Class="Test.MyTestControl"
Text="{Binding ElementName=MyTextBox, Path=Text}"
<TextBox x:Name="MyTextBox" Text="MyText" />
</base:BaseUserControl>
For some reason, I can't get the MyTextBox to update the Text property on the control itself.
If I add a:
<TextBlock Text="{Binding ElementName=MyTextBox, Path=Text}" />
Anywhere inside the control, the textblock shows the correct TextBox value so the binding definition doesn't seem to be the problem.
I have something else which shows the value of Text in that control... say something like:
<Window>
<StackPanel>
<test:MyTestControl x:Name="MyControl" />
<TextBlock Text="{Binding ElementName=MyControl, Path=Text}" />
</StackPanel>
</Window>
If I update the Text property on MyControlBase from any other means (codebehind, or whatever), it works, and I see the text changed on the textblock... but it doesn't work seem to update when the TextBox inside itself is updated.
Are there any limitations on binding to properties when you are inheriting a control?
PS: the code is obviously artificial and boilerplated for this question
Note: there is obviously something wrong with the binding on that property, since on the trace window, when creating the control, I get a:
System.Windows.Data Error: 4 : Cannot find source for binding with reference 'ElementName=MyTextBox'. BindingExpression:Path=Text; DataItem=null; target element is 'MyTestControl' (Name=''); target property is 'Text' (type 'String')
But it only happens for the `MyTestControl's property, and not for any other binding to the same property inside the XAML.
I believe the problem is that the MyTextBox hasn't been initialized when the BaseUserControl initializes itself and tries to bind with the Text property of the MyTextBox. At this stage, the MyTextBox doesn't exist, as a result you get the 'System.Windows.Data Error: 4 : Cannot find SOURCE for binding with reference'.
You can bind in code-behind after the InitializeComponent() in the CTOR of your MyTestControl.
public MyTestControl()
{
InitializeComponent();
Binding b = new Binding("Text");
b.Source = MyTextBox;
SetBinding(TextProperty, b);
}
Related
I'm trying to use the PropertyGrid component from PropertyTools to display information on an object. I can bind the object easily enough -- it's a property on my DataContext -- but one of the things that can't be derived from the object is the name that should be displayed in the tab header. (And I can't change that; the object I'm inspecting comes from a third party.) The proper name is a different property on my DataContext.
PropertyGrid has a way to change the way the tab header is displayed, by passing a DataTemplate to its TabHeaderTemplate property. But something bizarre happens inside of the template: my DataContext is gone, replaced by something else. When I try to say {Binding TabName} in the appropriate place inside the context, it errors out and tells me that TabName is not a valid property on class Tab. But my DataContext class isn't called Tab; that's something inside of PropertyTools's codebase!
I'm still new to WPF, so I have no clue what's going on here. Why is the in-scope DataContext that's perfectly valid in the rest of the XAML file being yoinked out from under me inside this template, and how can I fix it?
EDIT: Posting the XAML as requested. The template is literally just the simplest possible thing:
<UserControl.Resources>
<DataTemplate x:Key="HeaderTemplate">
<TextBlock Text="{Binding TabName}" />
</DataTemplate>
</UserControl.Resources>
And then further down the page,
<props:PropertyGrid
SelectedObject="{Binding Value}"
TabHeaderTemplate="{StaticResource HeaderTemplate}" />
But for some bizarre reason, in the template it's trying to interpret the binding inside the wrong DataContext!
In this case, just be sure to specify the source in your binding. There are a few ways to do this. One is to use the RelativeSource property of the Binding. Another is to use ElementName
Give your UserControl this attribute:
x:Name="Root".
Then change your binding to use it
<TextBlock Text="{Binding ElementName=Root, Path=DataContext.TabName}" />
Or use this:
<TextBlock Text="{Binding RelativeSource={RelativeSource AncestorType={x:Type local:MyUserControl}}, Path=DataContext.TabName}"/>
I am trying to wrap a TextBox in a custom UserControl and by then my custom UserControl has a Text dependency property. An example use of the custom UserControl would look like this :
<MyTextBoxWrapper Text="{Binding SomeProperty}"/>
and MyTextBoxWrapper looks like this :
<UserControl ...>
<TextBox x:Name="wrappedTextBox"/>
</UserControl>
I'd like my wrapper to work exactly like if it was written like this :
<UserControl ...>
<TextBox x:Name="wrappedTextBox" Text="{Binding SomeProperty}"/>
</UserControl>
My issue is that I can't manage to "transfer" the binding from the MyTextBoxWrapper.Text property to the TextBox.Text property. (kind of like binding the bindings themselves)
I only managed to obtain the binding used by MyTextBoxWrapper.Text with this :
myTextBoxWrapperInstance.GetBindingExpression(MyTextBoxWrapper.TextProperty);
How can I have the same binding being used for both properties? I don't necessarily need the same binding instance but I at least need the binding used by TextBox.Text to be created from the binding used by MyTextBoxWrapper.Text.
Bind the TextBox in the UserControl to the Text property of the UserControl itself:
<TextBox x:Name="wrappedTextBox"
Text="{Binding Text, RelativeSource={RelativeSource AncestorType=UserControl}}"/>
This doesn't fit my needs, I need to have the binding on TextBox.Text to be the same binding as the one on MyTextBoxWrapper.Text, what you gave me creates a different binding
Yes, a single binding always has a single target and single source.
You may try to register a callback for the custom Text property of the UserControl and programmatically bind the Text property of the TextBox to the same property.
Or make Text a property of type Binding.
My UserControl requires binding to the ancestor (the ancestor being the MainWindow) and to itself (it's code behind).
To bind to the ancestor, I'm using
DataContext="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorLevel=1,AncestorType=Window}}">
To bind a control to the code behind (and thus using the 'local' DataContext), I'm using
<TextBlock Text ="{Binding MyUC3Property}" Name="MyName" />
and in the code behind, setting it like
this.MyName.DataContext = this;
The above works fine, where I can bind to the codebehind and to the ancestor.
Now, I still want to bind to the code behind and the ancestor but set the DataContext in the XAML only (if possible).
I've tried
<TextBlock Text ="{Binding MyUC3Property}" DataContext="{Binding RelativeSource={RelativeSource Mode=Self}}" />
and ensured the constructor does not set the DataContext (since I want it all done in the XAML) - (although even if I do set this.DataContext = this; the error persists)
and the output window tells me there is a binding error.
System.Windows.Data Error: 40 : BindingExpression path error: 'MyUC3Property' property not found on 'object' ''TextBlock' (Name='')'. BindingExpression:Path=MyUC3Property; DataItem='TextBlock' (Name=''); target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String')
I guess I'm missing something obvious, but I can't tell what.
You should be able to bind to the user control the same way as you do to the window:
DataContext="{Binding RelativeSource={RelativeSource Mode=FindAncestor, AncestorLevel=1,AncestorType=UserControl}}">
What you have tried was referring to the relative source Self from the TextBox. However, in that context, Self refers to the TextBox, not to the enclosing user control.
for usercontrols you should never set the datacontext to self. check to comment from H.B. from here
i use ElementName Binding
<UserControl x:Name="uc">
<TextBlock Text="{Binding ElementName=uc, Path=MyDependencyPropertyDefinedInMyUserControl}"/>
using the usercontrol:
<Window>
<MyUserControl MyDependencyPropertyDefinedInMyUserControl="{Binding Path=MyValueForTheTextBox}"/>
i try to explain it a little bit for your textbox case (ignor my poor english btw :))
if you want create a usercontrol with a textbox and this usercontrol/textbox should show the text from differrent viewmodels in different views - then you have a problem as far as the viewmodels have different propertynames. now the dependency property in your usercontrol come into the game. you create a DP where all your viewmodels can bind to and you bind your textbox within your usercontrol just to the DP from your usercontrol.
First thing is that you should probably push your parent DataContext to the lower levels. This will give you "God" ViewMode shared between all nested screens.
Second is that you should probably use something like MVVMLights Messanger to have cleaner separation.
I have this xaml file in which I try to bind a Text-block Background to a static variable in another class, how can I achieve this ?
I know this might be silly but I just moved from Win-forms and feeling a little bit lost.
here is what I mean:
<TextBlock Text="some text"
TextWrapping="WrapWithOverflow"
Background="{Binding Path=SomeVariable}" />
First of all you can't bind to variable. You can bind only to properties from XAML.
For binding to static property you can do in this way (say you want to bind Text property of TextBlock) -
<TextBlock Text="{Binding Source={x:Static local:YourClassName.PropertyName}}"/>
where local is namespace where your class resides which you need to declare above in xaml file like this -
xmlns:local="clr-namespace:YourNameSpace"
You can't actually bind to a static property (INotifyPropertyChanged makes sense on instances only), so this should be enough...
{x:Static my:MyTestStaticClass.MyProperty}
or e.g.
<TextBox Text="{x:Static my:MyTestStaticClass.MyProperty}" Width="500" Height="100" />
make sure you include the namespace - i.e. define the my in the XAML like xmlns:my="clr-namespace:MyNamespace"
EDIT: binding from code
(There're some mixed answers on this part so I thought it made sense to expand, have it in one place)
OneTime binding:
You could just use textBlock.Text = MyStaticClass.Left (just careful where you place that, post-init)
TwoWay (or OneWayToSource) binding:
Binding binding = new Binding();
//binding.Source = typeof(MyStaticClass);
// System.InvalidOperationException: 'Binding.StaticSource cannot be set while using Binding.Source.'
binding.Path = new PropertyPath(typeof(MyStaticClass).GetProperty(nameof(MyStaticClass.Left)));
binding.Mode = BindingMode.TwoWay;
binding.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
this.SetBinding(Window.LeftProperty, binding);
...of course if you're setting Binding from the code remove any bindings in XAML.
OneWay (property changes from the source):
And if you'd need to update the target (i.e. the control's property, Window.Left in this case) on the source property changes, that can't be achieved with the static class (as per my comment above, you'd need the INotifyPropertyChanged implemented, so you could just use a wrapper class, implement INotifyPropertyChanged and wire that to a static property of your interest (providing you know how to track you static property's changes, i.e. this is more of a 'design' issue from this point on, I'd suggest redesigning and putting it all within one 'non-static' class).
You can use the newer x:Bind to do this simply using:
<TextBlock Text="{x:Bind YourClassName.PropertyName}"/>
I developed a user control in SilverLight that contains several child controls. Textboxes, ComboBoxes and so on.
The problem is, when I include that UserControl into a parent view and set the complete control to IsEnabled=False, the child controls in that specific UserControl are still enabled.
After all I found the problem.
Adding something like that, implies that the IsEnabled Binding is located in the UserControl binding, not as expected from myself in the DataContext of the parent.
<localControls:TeamEmployeeSelector Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2"
IsEnabled="{Binding CanModify}" DataContext="{Binding Confidentiality}"/>
QUESTION:
But there's still the question how I can bind the IsEnabled to the ViewModel of the Parent? Because it's not very elegant to copy the CanModify Property to the ViewModel of the Child Control.
Instead of modifying a binding in some way (for example you can make it dependent on other control name as it is proposed in other answer) I would move separate the control which will be disabled and control where DataContext will be changed. For example:
<ContentControl IsEnabled="{Binding CanModify}" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2">
<localControls:TeamEmployeeSelector DataContext="{Binding Confidentiality}"/>
</ContentControl>
Here is how I would do this.
Your TeamEmployeeSelector UserControl will contain a single root level element which by default is a Grid and is given the name "LayoutRoot".
Now you can bind the IsEnabled property of all the child elements to the UserControl like this:-
<TextBox IsEnabled="{Binding Parent.IsEnabled, ElementName=LayoutRoot}" ... />
By using element-to-element binding you do not need to copy the CanModify property in to child view models.
Some might suggest that you simply add an x:Name to your UserControl element and then bind directly to it rather than going via the Parent property of the root element as I do above. That'll work ok in Silverlight 4 but not in 3 or WP7. Personally I prefer the above.
This is a scoping issue. Generally, when creating a UserControl, you want to set itself as the DataContext for its sub-elements. This is most easily accomplished in the constructor:
UserControlExample() {
InitializeComponent();
RootElement.DataContext = this;
}
Where RootElement is the name you give to this first child (usually a Grid or panel) of your UserControl.
From here you can set natural bindings for your sub-elements like so:
<TextBox x:Name="MainTextBox" IsEnabled={Binding IsEnabled} />
This works, since TextBox inherits the DataContext of the parent layout panel.
Finally, if you want to have your UserControl's IsEnabled property to be related to its parent, this is best done at the point of declaration:
<Grid>
<UserControlExample IsEnabled={Binding CanModify} />
</Grid>
This way you keep your concerns separate. The sub-controls don't care what the UserControl is reflecting. They just need to know how to enable/disable when the control's IsEnabled property flips.
sub-controls IsEnabled bound to --> (UserControlExample is DataContext)
UserControlExample.IsEnabled bound to --> (VM is DataContext)
VM.CanModify
I don't know if it's possible in Silverlight, but in WPF I would use RelativeSource.
Have a look here.
Hope this help !
<localControls:TeamEmployeeSelector Grid.Row="1" Grid.Column="0"
Grid.ColumnSpan="2" IsEnabled="{Binding ElementName=SomeElementName_With_Parent_ViewModel, Path=DataContext.CanModify}" DataContext="{Binding Confidentiality}"/>