I want to set the datacontext of a TextBlock at XAML.
Resharper suggested this
<TextBlock Text="{Binding name}" Margin="50" d:DataContext="{d:DesignData Class1}" />
but when I run the application for some reason TextBlock has as its datacontext the class that I specified at View's code-behind and displays a wrong text
Views's code-behind
public partial class ViewA : UserControl {
public ViewA() {
InitializeComponent();
VmB vm = new VmB();
DataContext = vm;
}
}
So i want to display Class1 name property instead of VmB name property.
d:DataContext sets the DataContext for the visual designer only. If you want to bind to your class you need to set your actual DataContext to an instance of Class1. Where you get that instance from and how you set it is up to you.
Yes you just need to drop the Design parts from your xaml, so something like this ...
<TextBlock Text="{Binding name}" Margin="50" DataContext="{Binding Class1}" />
Related
I have a UserControl that I want to participate in data binding. I've set up the dependency properties in the user control, but can't get it work.
The uc displays the correct text when I call it with static text (e.g BlueText="ABC") . When i try to bind it to a local public property, it is always blank.
<src:BlueTextBox BlueText="Feeling blue" /> <!--OK-->
<src:BlueTextBox BlueText="{Binding Path=MyString}" /> <!--UserControl always BLANK!-->
<TextBox Text="{Binding Path=MyString}" Width="100"/> <!--Simple TextBox Binds OK-->
I've boiled the code down to the following simplified example. Here is the XAML of the UserControl:
<UserControl x:Class="Binding2.BlueTextBox" ...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Here is the code behind of the UserControl:
public partial class BlueTextBox : UserControl
{
public BlueTextBox()
{
InitializeComponent();
DataContext = this; // shouldn't do this - see solution
}
public static readonly DependencyProperty BlueTextProperty =
DependencyProperty.Register("BlueText", typeof(string), typeof(BlueTextBox));
public string BlueText
{
get { return GetValue(BlueTextProperty).ToString(); }
set { SetValue( BlueTextProperty, value.ToString() ); }
}
This seems like it should be really easy, but I can't make it work. Thanks for your help!
More info: When i was trying the fix suggested by Eugene, I noticed some peculiar behavior. I added a PropertyChangedCallback to the metadata; this allows me to watch the value of BlueText getting set. When setting the string to a static value (="feeling blue") the PropertyChanged event fires. The data binding case does not fire PropertyChanged. I think this means the data-bound value is not getting sent to the UserControl. (I think the constructor does not get called in the static case)
Solution: The problems were correctly identified by Arcturus and jpsstavares. First, I was overwriting the data binding when is set DataContext=this in the constructor of the control. This prevented the data bound value from getting set. I also had to name the control x:Name=root, and specify the Binding ElementName=root int the XAML. To get the TwoWay binding, I needed to set Mode=TwoWay in the caller. Here is the correct code:
<src:BlueTextBox BlueText="{Binding Path=MyString, Mode=TwoWay}}" /> <!--OK-->
Now the XAML in the UserControl:
<UserControl x:Class="Binding2.BlueTextBox" x:Name="root"...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding ElementName=root, Path=BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Finally I removed the DataContext=this in the constructor of the UserControl.
public BlueTextBox()
{
InitializeComponent();
//DataContext = this; -- don't do this
}
Thanks everyone for the tremendous help!
You set the DataContext in the Control to itself, thus overwriting the DataContext when using this Control in other controls. Taking your binding as example in your situation:
<src:BlueTextBox BlueText="{Binding Path=MyString}" />
Once loaded and all the Datacontext is set, it will look for the path MyString in your BlueTextBox thing control due to you setting the DataContext to it. I guess this is not how you intended this to work ;).
Solution:
Change the text binding either one of the 2 bindings:
{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type src:BlueTextBox}}, Path=BlueText}
or
Name your control Root (or something like that)
<UserControl x:Name="Root"
{Binding ElementName=Root, Path=BlueText}
And remove the
DataContext = this;
from the constructor of your UserControl and it should work like a charm..
I think in this case you need to set the ElementName property in the binding. Something like this:
<UserControl x:Class="Binding2.BlueTextBox" x:Name="blueTextBox"...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding ElementName=blueTextBox, Path=BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Possibly you need to add to your property FrameworkPropertyMetadata where specify FrameworkPropertyMetadataOptions.AffectsRender and AffectsMeasure.
FrameworkPropertyMetadataOptions enumeration MSDN article
I know this is an old topic but still.
Also mention the PropertyChangedCallback on the UIPropertyMetadata during registering your DP
In WPF I have a window that includes a user control. The window and user control each have a view model. I want to pass a parameter from the window's VM to the UC's VM. After a fair amount of looking, I haven't found a way.
The window XAML sets its data context to its VM. The UC includes a custom dependency property for the parameter. I want to use SetBinding to bind the DP to the UC VM.
If I set the UC data context to its VM, then the parameter binding doesn't work. If I don't set the UC data context then the parameter binding works but the UC VM is not referenced.
How can I pass a parameter AND bind to the UC VM?
UC XAML
<UserControl x:Name="userControl" x:Class="Test_Paramaterized_UserControl_with_MVVM.UserControl1"
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:Test_Paramaterized_UserControl_with_MVVM"
xmlns:view="clr-namespace:Daavlin.SmartTouch.STUV_WPF.View"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300">
<Grid Margin="10">
<Border BorderThickness="3" BorderBrush="Black" Padding="10">
<StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
<StackPanel Orientation="Horizontal">
<TextBlock Text="UserControl1 View: "/>
<TextBlock Text="{Binding ElementName=userControl, Path=PropUserControlView, Mode=OneWay}" FontWeight="Bold"/>
</StackPanel>
<Rectangle Height="5"/>
<StackPanel Orientation="Horizontal">
<TextBlock Text="UserControl1 ViewModel: " />
<TextBlock Text="{Binding PropUserControlViewModel, FallbackValue=propUserControlViewModel 2}" FontWeight="Bold">
<TextBlock.DataContext>
<local:UserControl1ViewModel/>
</TextBlock.DataContext>
</TextBlock>
</StackPanel>
</StackPanel>
</Border>
</Grid>
</UserControl>
UC code-behind & VM
public partial class UserControl1 : UserControl
{
public UserControl1()
{
InitializeComponent();
}
public string PropUserControlView { get => (string)GetValue(PropUserControlViewProperty); set => SetValue(PropUserControlViewProperty, value); }
public static readonly DependencyProperty PropUserControlViewProperty =
DependencyProperty.Register(nameof(PropUserControlView), typeof(string), typeof(UserControl1),
new PropertyMetadata(null, DependencyPropertyChanged));
private static void DependencyPropertyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
var x = dependencyPropertyChangedEventArgs.NewValue;
}
}
public class UserControl1ViewModel : ObservableObject
{
public string PropUserControlViewModel { get => _propUserControlViewModel; set => SetField(ref _propUserControlViewModel, value); }
private string _propUserControlViewModel = "value from UserControl-ViewModel";
}
Window XAML
<Window x:Class="Test_Paramaterized_UserControl_with_MVVM.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Test_Paramaterized_UserControl_with_MVVM"
Title="MainWindow" >
<Window.DataContext>
<local:MainWindowViewModel />
</Window.DataContext>
<Grid VerticalAlignment="Top" >
<StackPanel VerticalAlignment="Center" HorizontalAlignment="Center" Margin="20">
<StackPanel Orientation="Horizontal">
<TextBlock Text="MainWindow1 ViewModel: "/>
<TextBox Text="{Binding PropWindowViewModel, UpdateSourceTrigger=PropertyChanged}" FontWeight="Bold"/>
</StackPanel>
<Rectangle Height="10"/>
<StackPanel Orientation="Horizontal">
<TextBlock Text="UserControl1 (fixed value Fixed): " VerticalAlignment="Center"/>
<local:UserControl1 PropUserControlView="Fixed"/>
</StackPanel>
<Rectangle Height="10"/>
<StackPanel Orientation="Horizontal">
<TextBlock Text="UserControl1 (bound to MainWindows VM): " VerticalAlignment="Center"/>
<local:UserControl1 PropUserControlView="{Binding PropWindowViewModel}"/>
</StackPanel>
</StackPanel>
</Grid>
</Window>
Window code-behind & VM
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
}
}
public class MainWindowViewModel : ObservableObject
{
public string PropWindowViewModel { get => _propWindowViewModel; set => SetField(ref _propWindowViewModel, value); }
private string _propWindowViewModel = "valuefrom Window-VIewModel";
}
As far as I understood, what you meant was :-
1) You have a user control which has its own view model.
2) You have a Window where you have its own view model.
You want to link both and pass parameters from your WindowViewModel to UserControlViewModel.
What you can do is, Keep a property (e.g. UCViewModel) of type UserControlViewModel in your WindowViewModel and set the datacontext of the user control in your XAML to
<local:UserControl1 DataContext="{Binding UCViewModel}" .../>
Now that you can access anything that is there in your UserControlViewModel via WindowViewModel, you can set any property value OR pass any parameter to your UserControlViewModel from WindowViewModel.
If you need a code reference, let me know. We have been using user controls in a similar way and it works fine.
I want to use SetBinding to bind the DP to the UC VM.
Is that really a requirement? SetBinding() requires that the target property be a dependency property, which in turn requires that the target object be a dependency object. Your view model object is not a dependency object, and of course none of its properties are dependency properties.
Achieving that goal would require a much bigger change to your code than is otherwise apparently necessary.
If I set the UC data context to its VM, then the parameter binding doesn't work
Why not? You didn't show code that attempts this, so it's difficult to understand what you mean here. It's not a good idea to have the user control set its own DataContext anyway. That property is public, and you don't want to expose your implementation details to client code. Doing so invites bugs where the client code has set the DataContext to the wrong thing, disabling everything in your UserControl.
But that said, if by "parameter binding" you mean the binding in the MainWindow XAML, assigning {Binding PropWindowViewModel} to the PropUserControlView property of the user control, then just setting the DataContext of the user control should not affect that. You still have the dependency property in the user control, and anything bound that within the user control should still work.
Finally, it's not entirely clear why you want the dependency property tied to the view model. In the user control's XAML, you can (as you've already done) bind directly to the user control's dependency property. There's no need for a property in the view model to replicate that.
Maybe you have code in the view model somewhere else that wants to respond to changes in this value? It's not clear, and it's difficult to give the best advice without knowing the whole story.
All that said, the code you posted above can be made to work with a couple of small changes. First, you'll need to expose the TextBlock where you've created the view model, so that the user control code-behind has access to it:
<TextBlock x:Name="textBlock1" Text="{Binding PropUserControlViewModel, FallbackValue=propUserControlViewModel 2}" FontWeight="Bold">
<TextBlock.DataContext>
<l:UserControl1ViewModel/>
</TextBlock.DataContext>
</TextBlock>
I.e. add the x:Name="textBlock1" to the declaration.
Then, you need to use the property-change notification for your dependency property to update the view model property any time the dependency property changes:
private static void DependencyPropertyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
UserControl1 uc = (UserControl1)dependencyObject;
UserControl1ViewModel vm = (UserControl1ViewModel)uc.textBlock1.DataContext;
vm.PropUserControlViewModel = (string)dependencyPropertyChangedEventArgs.NewValue;
}
The above works in your limited example, but you'll probably want to give the DependencyPropertyChanged() method a more descriptive name, specific to the actual property in question.
If you do choose to mirror the dependency property in the view model this way, IMHO a better way to do that would be to set the user control's root element (i.e. the Grid) so that its data context is your view model, and then throughout the rest of the XAML, bind only to the view model. Mixing the view model and dependency property is not wrong per se, but it does introduce an inconsistency that can make it harder to test and maintain the code.
I have a private field
private static Double myValue;
in the application MainWindow class. And there (in the MainWindow class) I defined a property
public static Double MytValue
{
get { return myValue; }
}
In the structure of the MainWindow class I have a TextBox. I'm in need of binding it to the MytValue property. In XAML I write:
<TextBox Name="tbxMyValue" Grid.Row="1" Grid.Column="2" TextAlignment="Center"
Text="{Binding Path=MyValue}" Width="Auto" Margin="10,0,10,15" IsEnabled="True" />
But it has no effect. I see nothing in the TextBox while myValue variable has a value. Why? Please help me.
I like to set the DataContext in the Window section
<Window x:Class="Gabe3a.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:Gabe3a"
xmlns:scm="clr-namespace:System.ComponentModel;assembly=WindowsBase"
xmlns:System="clr-namespace:System;assembly=mscorlib"
DataContext="{Binding RelativeSource={RelativeSource self}}"
Title="Gabriel Main Ver 3a01" Icon="faviconw.ico" Height="600" Width="800">
You need to set the DataContext behind the Window for that binding to work
There are two layers to an application with WPF: the UI layer and the data layer.
The Data layer for an application starts out as null, and you can set it using the DataContext property.
Whenever you do a basic binding in WPF, you are binding to the DataContext. So Text="{Binding Path=MyValue}" is actually saying "Get the MyValue property from the current DataContext".
You could simply set the DataContext in your code behind:
MyWindow.DataContext = this;
Or you can use a RelativeSource binding to tell WPF to get the MyValue property from somewhere else, such as telling it to get it from the closest Window it finds when navigating up the VisualTree:
Text="{Binding Path=MyValue, RelativeSource={
RelativeSource AncestorType={x:Type Window}}}"
I actually have an article on my blog about the DataContext that I'd recommend reading if you're new to WPF and the DataContext: What is this "DataContext" you speak of?
It's not how it works. Binding to static properties; {Binding Source={x:Static local:Application.MyValue}}
Note that your field needs to be property & public. If you want to go with your solution, you need to set DataContext as {RelativeSource Self}.
In file MainWindow.xaml.cs in constructor add this line:
DataContext = this;
after InitializeComponent();
I have a window which has a usercontrol in it . This usercontrol's RequestObject property bound to SearchArgumentObject property of ViewModel of the window.
This is listing from my window class
<Grid DataContext="{Binding SearchArgumentObject, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}">
<guiLib:RegCardSearchForm x:Name="SearchParametrsUC" Grid.Row="1" RequestObject="{Binding .,Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
</Grid>
In Usercontrol class I created dependency property:
This is listing from my userControl class
public static DependencyProperty RequestObjectProperty = DependencyProperty.Register("RequestObject", typeof(RegistrationCardSearch), typeof(RegCardSearchForm));
public RegistrationCardSearch RequestObject
{
get
{
return (RegistrationCardSearch)GetValue(RequestObjectProperty);
}
set
{
SetValue(RequestObjectProperty, value);
}
}
On the level of the usecontrol everything works fine and RequestOject property changed.
But in my window class I can't see modification of SearchArgumentObject property which was made in usercontrol.
How can I get modefied property value? I think answer to this question is very trivial but I can't find solution.
Setting the DataContext on the Grid isn't doing anything but breaking the two-way linking of your properties. Skip the extra step and bind the VM property to the control property that you want to pick up changes from instead:
<Grid>
<guiLib:RegCardSearchForm x:Name="SearchParametrsUC" Grid.Row="1"
RequestObject="{Binding SearchArgumentObject, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
</Grid>
The code for your Window class is setting the DataContext of the Grid to a property obtained from a binding to a property on another object's DataContext further up the tree. Do you have the Window's DataContext set elsewhere?
Let's say that the object which is supplying the SearchArgumentObject is named SearchWindowViewModel. In the code-behind of the Window, you would have the following code (in the constructor, for example):
DataContext = new SearchWindowViewModel();
Now, all the properties that SearchWindowViewModel exposes are available to the Window. To bind the SearchWindowViewModel.SearchArgumentObject to the UserControl's RequestObject property, you would have the following XAML:
<Grid>
<guiLib:RegCardSearchForm x:Name=SearchParametersUC Grid.Row=1
RequestObject={Binding SearchArgumentObject />
</Grid>
If you don't want to set the Window's DataContext, you can set the Grid's DataContext using the same type of code as I used above, and the binding in the XAML would remain the same.
Hope that helps.
I have a UserControl that I want to participate in data binding. I've set up the dependency properties in the user control, but can't get it work.
The uc displays the correct text when I call it with static text (e.g BlueText="ABC") . When i try to bind it to a local public property, it is always blank.
<src:BlueTextBox BlueText="Feeling blue" /> <!--OK-->
<src:BlueTextBox BlueText="{Binding Path=MyString}" /> <!--UserControl always BLANK!-->
<TextBox Text="{Binding Path=MyString}" Width="100"/> <!--Simple TextBox Binds OK-->
I've boiled the code down to the following simplified example. Here is the XAML of the UserControl:
<UserControl x:Class="Binding2.BlueTextBox" ...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Here is the code behind of the UserControl:
public partial class BlueTextBox : UserControl
{
public BlueTextBox()
{
InitializeComponent();
DataContext = this; // shouldn't do this - see solution
}
public static readonly DependencyProperty BlueTextProperty =
DependencyProperty.Register("BlueText", typeof(string), typeof(BlueTextBox));
public string BlueText
{
get { return GetValue(BlueTextProperty).ToString(); }
set { SetValue( BlueTextProperty, value.ToString() ); }
}
This seems like it should be really easy, but I can't make it work. Thanks for your help!
More info: When i was trying the fix suggested by Eugene, I noticed some peculiar behavior. I added a PropertyChangedCallback to the metadata; this allows me to watch the value of BlueText getting set. When setting the string to a static value (="feeling blue") the PropertyChanged event fires. The data binding case does not fire PropertyChanged. I think this means the data-bound value is not getting sent to the UserControl. (I think the constructor does not get called in the static case)
Solution: The problems were correctly identified by Arcturus and jpsstavares. First, I was overwriting the data binding when is set DataContext=this in the constructor of the control. This prevented the data bound value from getting set. I also had to name the control x:Name=root, and specify the Binding ElementName=root int the XAML. To get the TwoWay binding, I needed to set Mode=TwoWay in the caller. Here is the correct code:
<src:BlueTextBox BlueText="{Binding Path=MyString, Mode=TwoWay}}" /> <!--OK-->
Now the XAML in the UserControl:
<UserControl x:Class="Binding2.BlueTextBox" x:Name="root"...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding ElementName=root, Path=BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Finally I removed the DataContext=this in the constructor of the UserControl.
public BlueTextBox()
{
InitializeComponent();
//DataContext = this; -- don't do this
}
Thanks everyone for the tremendous help!
You set the DataContext in the Control to itself, thus overwriting the DataContext when using this Control in other controls. Taking your binding as example in your situation:
<src:BlueTextBox BlueText="{Binding Path=MyString}" />
Once loaded and all the Datacontext is set, it will look for the path MyString in your BlueTextBox thing control due to you setting the DataContext to it. I guess this is not how you intended this to work ;).
Solution:
Change the text binding either one of the 2 bindings:
{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type src:BlueTextBox}}, Path=BlueText}
or
Name your control Root (or something like that)
<UserControl x:Name="Root"
{Binding ElementName=Root, Path=BlueText}
And remove the
DataContext = this;
from the constructor of your UserControl and it should work like a charm..
I think in this case you need to set the ElementName property in the binding. Something like this:
<UserControl x:Class="Binding2.BlueTextBox" x:Name="blueTextBox"...
<Grid>
<TextBox x:Name="myTextBox" Text="{Binding ElementName=blueTextBox, Path=BlueText}" Foreground="Blue" Width="100" Height="26" />
</Grid>
Possibly you need to add to your property FrameworkPropertyMetadata where specify FrameworkPropertyMetadataOptions.AffectsRender and AffectsMeasure.
FrameworkPropertyMetadataOptions enumeration MSDN article
I know this is an old topic but still.
Also mention the PropertyChangedCallback on the UIPropertyMetadata during registering your DP