The instance of the class is a private member of the view code exposed as a public property named "ViewModel".
You are setting the DataContext of the Grid to a string equal to "ViewModel". You need to make sure the DataContext property is correctly set to actual ViewModel object instance, either with a binding or via code behind.
For more information, see my answer to the question What is DataContext for?
I'm agree with the Rachel's answer. An easy way to set the DataContext of your Grid could be this:
<Window.Resources>
<YourNamespace:ViewModel x:Key="ViewModel"/>
</Window.Resources>
<Grid DataContext="{StaticResource ViewModel}">
<TextBox Text="{Binding Path=TestName}" Height="23" HorizontalAlignment="Left" Margin="12,12,0,0" Name="TextBox1" VerticalAlignment="Top" Width="479" />
</Grid>
This way you don't need to touch the code behind of your Window/UserControl.
If you don't want to change the code in your view and and want to keep your ViewModel property, then you could also do this:
Public Class View Inherits Window
Private m_ViewModel As ViewModel
Public Property ViewModel() As ViewModel
Get
Return m_ViewModel
End Get
Set
m_ViewModel = Value
End Set
End Property
Public Sub New()
InitializeComponent()
ViewModel = New ViewModel()
DataContext = ViewModel
End Sub
End Class
So you don't need to set the DataContext in your view, just do this:
<Grid>
<TextBox Text="{Binding Path=TestName}" Height="23" HorizontalAlignment="Left" Margin="12,12,0,0" Name="TextBox1" VerticalAlignment="Top" Width="479" />
</Grid>
Related
I created a small File Browser Control:
<UserControl x:Class="Test.UserControls.FileBrowserControl"
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"
mc:Ignorable="d"
d:DesignHeight="44" d:DesignWidth="461" Name="Control">
<Grid Margin="3">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<TextBox Margin="3" Text="{Binding SelectedFile}" IsReadOnly="True" TextWrapping="Wrap" />
<Button HorizontalAlignment="Right" Margin="3" Width="100" Content="Browse" Grid.Column="1" Command="{Binding BrowseCommand}" />
</Grid>
</UserControl>
With the following code behind:
public partial class FileBrowserControl : UserControl
{
public ICommand BrowseCommand { get; set; }
//The dependency property
public static DependencyProperty SelectedFileProperty = DependencyProperty.Register("SelectedFile",
typeof(string),typeof(FileBrowserControl), new PropertyMetadata(String.Empty));
public string SelectedFile { get{ return (string)GetValue(SelectedFileProperty);} set{ SetValue(SelectedFileProperty, value);}}
//For my first test, this is a static string
public string Filter { get; set; }
public FileBrowserControl()
{
InitializeComponent();
BrowseCommand = new RelayCommand(Browse);
Control.DataContext = this;
}
private void Browse()
{
SaveFileDialog dialog = new SaveFileDialog();
if (Filter != null)
{
dialog.Filter = Filter;
}
if (dialog.ShowDialog() == true)
{
SelectedFile = dialog.FileName;
}
}
}
And I use it like this:
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" Filter="XSLT File (*.xsl)|*.xsl|All Files (*.*)|*.*"/>
(SelectedFile is Property of the ViewModel of the usercontrol using this control)
Currently the issue is that when I click on Browse, the textbox in the usercontrol is correctly updating, but the SelectedFile property of the viewmodel parent control is not set(no call to the set property).
If I set the Mode of the binding to TwoWay, I got this exception:
An unhandled exception of type 'System.StackOverflowException' occurred in Unknown Module.
So what did I do wrong?
The problem is that you set your UserControl's DataContext to itself in its constructor:
DataContext = this;
You should not do that, because it breaks any DataContext based Bindings, i.e. to a view model instance that is provided by property value inheritance of the DataContext property
Instead you would change the binding in the UserControl's XAML like this:
<TextBox Text="{Binding SelectedFile,
RelativeSource={RelativeSource AncestorType=UserControl}}" />
Now, when you use your UserControl and write a binding like
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" />
the SelectedFile property gets bound to a SelectedFile property in your view model, which should be in the DataContext inherited from a parent control.
Do not ever set DataContext of UserControl inside usercontrol:
THIS IS WRONG:
this.DataContext = someDataContext;
because if somebody will use your usercontrol, its common practice to set its datacontext and it is in conflict with what you have set previously
<my:SomeUserControls DataContext="{Binding SomeDataContext}" />
Which one will be used? Well, it depends...
The same applies to Name property. you should not set name to UserControl like this:
<UserControl x:Class="WpfApplication1.SomeUserControl" Name="MyUserControl1" />
because it is in conflict with
<my:SomeUserControls Name="SomeOtherName" />
SOLUTION:
In your control, just use RelativeSource Mode=FindAncestor:
<TextBox Text="{Binding SelectedFile, RelativeSource={RelativeSource AncestorType="userControls:FileBrowserControl"}" />
To your question on how are all those third party controls done: They use TemplateBinding. But TemplateBinding can be used only in ControlTemplate. http://www.codeproject.com/Tips/599954/WPF-TemplateBinding-with-ControlTemplate
In usercontrol the xaml represents Content of UserControl, not ControlTemplate/
Using this:
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" ...
The FileBrowserControl's DataContext has already been set to itself, therefore you are effectively asking to bind to the SelectedFile where the DataContext is the FileBrowserControl, not the parent ViewModel.
Give your View a name and use an ElementName binding instead.
SelectedFile="{Binding DataContext.SelectedFile, ElementName=element}"
I created a small File Browser Control:
<UserControl x:Class="Test.UserControls.FileBrowserControl"
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"
mc:Ignorable="d"
d:DesignHeight="44" d:DesignWidth="461" Name="Control">
<Grid Margin="3">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<TextBox Margin="3" Text="{Binding SelectedFile}" IsReadOnly="True" TextWrapping="Wrap" />
<Button HorizontalAlignment="Right" Margin="3" Width="100" Content="Browse" Grid.Column="1" Command="{Binding BrowseCommand}" />
</Grid>
</UserControl>
With the following code behind:
public partial class FileBrowserControl : UserControl
{
public ICommand BrowseCommand { get; set; }
//The dependency property
public static DependencyProperty SelectedFileProperty = DependencyProperty.Register("SelectedFile",
typeof(string),typeof(FileBrowserControl), new PropertyMetadata(String.Empty));
public string SelectedFile { get{ return (string)GetValue(SelectedFileProperty);} set{ SetValue(SelectedFileProperty, value);}}
//For my first test, this is a static string
public string Filter { get; set; }
public FileBrowserControl()
{
InitializeComponent();
BrowseCommand = new RelayCommand(Browse);
Control.DataContext = this;
}
private void Browse()
{
SaveFileDialog dialog = new SaveFileDialog();
if (Filter != null)
{
dialog.Filter = Filter;
}
if (dialog.ShowDialog() == true)
{
SelectedFile = dialog.FileName;
}
}
}
And I use it like this:
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" Filter="XSLT File (*.xsl)|*.xsl|All Files (*.*)|*.*"/>
(SelectedFile is Property of the ViewModel of the usercontrol using this control)
Currently the issue is that when I click on Browse, the textbox in the usercontrol is correctly updating, but the SelectedFile property of the viewmodel parent control is not set(no call to the set property).
If I set the Mode of the binding to TwoWay, I got this exception:
An unhandled exception of type 'System.StackOverflowException' occurred in Unknown Module.
So what did I do wrong?
The problem is that you set your UserControl's DataContext to itself in its constructor:
DataContext = this;
You should not do that, because it breaks any DataContext based Bindings, i.e. to a view model instance that is provided by property value inheritance of the DataContext property
Instead you would change the binding in the UserControl's XAML like this:
<TextBox Text="{Binding SelectedFile,
RelativeSource={RelativeSource AncestorType=UserControl}}" />
Now, when you use your UserControl and write a binding like
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" />
the SelectedFile property gets bound to a SelectedFile property in your view model, which should be in the DataContext inherited from a parent control.
Do not ever set DataContext of UserControl inside usercontrol:
THIS IS WRONG:
this.DataContext = someDataContext;
because if somebody will use your usercontrol, its common practice to set its datacontext and it is in conflict with what you have set previously
<my:SomeUserControls DataContext="{Binding SomeDataContext}" />
Which one will be used? Well, it depends...
The same applies to Name property. you should not set name to UserControl like this:
<UserControl x:Class="WpfApplication1.SomeUserControl" Name="MyUserControl1" />
because it is in conflict with
<my:SomeUserControls Name="SomeOtherName" />
SOLUTION:
In your control, just use RelativeSource Mode=FindAncestor:
<TextBox Text="{Binding SelectedFile, RelativeSource={RelativeSource AncestorType="userControls:FileBrowserControl"}" />
To your question on how are all those third party controls done: They use TemplateBinding. But TemplateBinding can be used only in ControlTemplate. http://www.codeproject.com/Tips/599954/WPF-TemplateBinding-with-ControlTemplate
In usercontrol the xaml represents Content of UserControl, not ControlTemplate/
Using this:
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" ...
The FileBrowserControl's DataContext has already been set to itself, therefore you are effectively asking to bind to the SelectedFile where the DataContext is the FileBrowserControl, not the parent ViewModel.
Give your View a name and use an ElementName binding instead.
SelectedFile="{Binding DataContext.SelectedFile, ElementName=element}"
I created a small File Browser Control:
<UserControl x:Class="Test.UserControls.FileBrowserControl"
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"
mc:Ignorable="d"
d:DesignHeight="44" d:DesignWidth="461" Name="Control">
<Grid Margin="3">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<TextBox Margin="3" Text="{Binding SelectedFile}" IsReadOnly="True" TextWrapping="Wrap" />
<Button HorizontalAlignment="Right" Margin="3" Width="100" Content="Browse" Grid.Column="1" Command="{Binding BrowseCommand}" />
</Grid>
</UserControl>
With the following code behind:
public partial class FileBrowserControl : UserControl
{
public ICommand BrowseCommand { get; set; }
//The dependency property
public static DependencyProperty SelectedFileProperty = DependencyProperty.Register("SelectedFile",
typeof(string),typeof(FileBrowserControl), new PropertyMetadata(String.Empty));
public string SelectedFile { get{ return (string)GetValue(SelectedFileProperty);} set{ SetValue(SelectedFileProperty, value);}}
//For my first test, this is a static string
public string Filter { get; set; }
public FileBrowserControl()
{
InitializeComponent();
BrowseCommand = new RelayCommand(Browse);
Control.DataContext = this;
}
private void Browse()
{
SaveFileDialog dialog = new SaveFileDialog();
if (Filter != null)
{
dialog.Filter = Filter;
}
if (dialog.ShowDialog() == true)
{
SelectedFile = dialog.FileName;
}
}
}
And I use it like this:
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" Filter="XSLT File (*.xsl)|*.xsl|All Files (*.*)|*.*"/>
(SelectedFile is Property of the ViewModel of the usercontrol using this control)
Currently the issue is that when I click on Browse, the textbox in the usercontrol is correctly updating, but the SelectedFile property of the viewmodel parent control is not set(no call to the set property).
If I set the Mode of the binding to TwoWay, I got this exception:
An unhandled exception of type 'System.StackOverflowException' occurred in Unknown Module.
So what did I do wrong?
The problem is that you set your UserControl's DataContext to itself in its constructor:
DataContext = this;
You should not do that, because it breaks any DataContext based Bindings, i.e. to a view model instance that is provided by property value inheritance of the DataContext property
Instead you would change the binding in the UserControl's XAML like this:
<TextBox Text="{Binding SelectedFile,
RelativeSource={RelativeSource AncestorType=UserControl}}" />
Now, when you use your UserControl and write a binding like
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" />
the SelectedFile property gets bound to a SelectedFile property in your view model, which should be in the DataContext inherited from a parent control.
Do not ever set DataContext of UserControl inside usercontrol:
THIS IS WRONG:
this.DataContext = someDataContext;
because if somebody will use your usercontrol, its common practice to set its datacontext and it is in conflict with what you have set previously
<my:SomeUserControls DataContext="{Binding SomeDataContext}" />
Which one will be used? Well, it depends...
The same applies to Name property. you should not set name to UserControl like this:
<UserControl x:Class="WpfApplication1.SomeUserControl" Name="MyUserControl1" />
because it is in conflict with
<my:SomeUserControls Name="SomeOtherName" />
SOLUTION:
In your control, just use RelativeSource Mode=FindAncestor:
<TextBox Text="{Binding SelectedFile, RelativeSource={RelativeSource AncestorType="userControls:FileBrowserControl"}" />
To your question on how are all those third party controls done: They use TemplateBinding. But TemplateBinding can be used only in ControlTemplate. http://www.codeproject.com/Tips/599954/WPF-TemplateBinding-with-ControlTemplate
In usercontrol the xaml represents Content of UserControl, not ControlTemplate/
Using this:
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" ...
The FileBrowserControl's DataContext has already been set to itself, therefore you are effectively asking to bind to the SelectedFile where the DataContext is the FileBrowserControl, not the parent ViewModel.
Give your View a name and use an ElementName binding instead.
SelectedFile="{Binding DataContext.SelectedFile, ElementName=element}"
I created a small File Browser Control:
<UserControl x:Class="Test.UserControls.FileBrowserControl"
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"
mc:Ignorable="d"
d:DesignHeight="44" d:DesignWidth="461" Name="Control">
<Grid Margin="3">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*"/>
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<TextBox Margin="3" Text="{Binding SelectedFile}" IsReadOnly="True" TextWrapping="Wrap" />
<Button HorizontalAlignment="Right" Margin="3" Width="100" Content="Browse" Grid.Column="1" Command="{Binding BrowseCommand}" />
</Grid>
</UserControl>
With the following code behind:
public partial class FileBrowserControl : UserControl
{
public ICommand BrowseCommand { get; set; }
//The dependency property
public static DependencyProperty SelectedFileProperty = DependencyProperty.Register("SelectedFile",
typeof(string),typeof(FileBrowserControl), new PropertyMetadata(String.Empty));
public string SelectedFile { get{ return (string)GetValue(SelectedFileProperty);} set{ SetValue(SelectedFileProperty, value);}}
//For my first test, this is a static string
public string Filter { get; set; }
public FileBrowserControl()
{
InitializeComponent();
BrowseCommand = new RelayCommand(Browse);
Control.DataContext = this;
}
private void Browse()
{
SaveFileDialog dialog = new SaveFileDialog();
if (Filter != null)
{
dialog.Filter = Filter;
}
if (dialog.ShowDialog() == true)
{
SelectedFile = dialog.FileName;
}
}
}
And I use it like this:
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" Filter="XSLT File (*.xsl)|*.xsl|All Files (*.*)|*.*"/>
(SelectedFile is Property of the ViewModel of the usercontrol using this control)
Currently the issue is that when I click on Browse, the textbox in the usercontrol is correctly updating, but the SelectedFile property of the viewmodel parent control is not set(no call to the set property).
If I set the Mode of the binding to TwoWay, I got this exception:
An unhandled exception of type 'System.StackOverflowException' occurred in Unknown Module.
So what did I do wrong?
The problem is that you set your UserControl's DataContext to itself in its constructor:
DataContext = this;
You should not do that, because it breaks any DataContext based Bindings, i.e. to a view model instance that is provided by property value inheritance of the DataContext property
Instead you would change the binding in the UserControl's XAML like this:
<TextBox Text="{Binding SelectedFile,
RelativeSource={RelativeSource AncestorType=UserControl}}" />
Now, when you use your UserControl and write a binding like
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" />
the SelectedFile property gets bound to a SelectedFile property in your view model, which should be in the DataContext inherited from a parent control.
Do not ever set DataContext of UserControl inside usercontrol:
THIS IS WRONG:
this.DataContext = someDataContext;
because if somebody will use your usercontrol, its common practice to set its datacontext and it is in conflict with what you have set previously
<my:SomeUserControls DataContext="{Binding SomeDataContext}" />
Which one will be used? Well, it depends...
The same applies to Name property. you should not set name to UserControl like this:
<UserControl x:Class="WpfApplication1.SomeUserControl" Name="MyUserControl1" />
because it is in conflict with
<my:SomeUserControls Name="SomeOtherName" />
SOLUTION:
In your control, just use RelativeSource Mode=FindAncestor:
<TextBox Text="{Binding SelectedFile, RelativeSource={RelativeSource AncestorType="userControls:FileBrowserControl"}" />
To your question on how are all those third party controls done: They use TemplateBinding. But TemplateBinding can be used only in ControlTemplate. http://www.codeproject.com/Tips/599954/WPF-TemplateBinding-with-ControlTemplate
In usercontrol the xaml represents Content of UserControl, not ControlTemplate/
Using this:
<userControls:FileBrowserControl SelectedFile="{Binding SelectedFile}" ...
The FileBrowserControl's DataContext has already been set to itself, therefore you are effectively asking to bind to the SelectedFile where the DataContext is the FileBrowserControl, not the parent ViewModel.
Give your View a name and use an ElementName binding instead.
SelectedFile="{Binding DataContext.SelectedFile, ElementName=element}"
Another post describes how to access a codebehind variable in XAML.
However, I'd like to access a variable in codebehind object from XAML. The codebehind object, called FeedData, is declared as a dependency property of type FeedEntry. This class is just a container class with string and datetime properties.
Codebehind's property definitition is this:
public FeedEntry FeedData
{
get { return (FeedEntry)GetValue(FeedDataProperty); }
set { SetValue(FeedDataProperty, value); }
}
public static readonly DependencyProperty FeedDataProperty =
DependencyProperty.Register("FeedData", typeof(FeedReaderDll.FeedEntry), typeof(FeedItemUserControl),
new FrameworkPropertyMetadata(new FeedEntry(){ Title="Hi!", Published=DateTime.Now }));
In XAML I'm doing this, which doesn't work:
<UserControl x:Class="FeedPhysics.UserControls.FeedItemUserControl"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Height="40" Width="200"
Background="Blue"
DataContext="{Binding RelativeSource={RelativeSource Self}}"
x:Name="xRoot">
<StackPanel>
<TextBlock Text="{Binding Title}" Foreground="White"/>
<TextBlock Text="{Binding Published}" Foreground="White"/>
</StackPanel>
</UserControl>
But if I override Window's datacontext setting in codebehind's contructor, it will work! Like this:
xRoot.DataContext = FeedData;
I understand why it works when datacontext is set in codebehing. But I'd like to find out a way to grab variables within an object that is declared in codebehind. Because, everything should be doable from XAML, right?
Thanks for answers in advance.
Try setting the StackPanel's DataContext to the FeedData object:
<StackPanel DataContext="{Binding FeedData}">
...
This will force the StackPanel to look at the DependencyProperty, and all elements in it will be referenced as properties of FeedData.
As long as you define the DataContext as "FeedData" somewhere in the logical tree above the visual elements you are binding to properties of it, it will work.