Binding between my usercontrol and ViewModel - mvvm

Question

Can not do Binding
Random (MyViewModel) -> VMTestValue (MyViewModel) -> TestUserControl (MainWindow)
"MyViewModel" is ViewModel for "MainWindow"
All project: http://rusfolder.com/32608140
TestUserControl.xaml
<UserControl x:Class="TestBinding.TestUserControl"
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"
Background="Green"
d:DesignHeight="300" d:DesignWidth="300">
<Grid>
<TextBlock Background="Gray" Margin="50" FontSize="18" Text="{Binding TestValue}" />
<Rectangle Height="200" Width="{Binding TestValue}" Fill="#FFFF1717" />
</Grid>
</UserControl>
TestUserControl.cs
...
public TestUserControl()
{
InitializeComponent();
this.DataContext = this;
}
public static readonly DependencyProperty TestValueProperty =
DependencyProperty.Register("TestValue", typeof(int), typeof(TestUserControl),
new FrameworkPropertyMetadata((int)255)
);
public int TestValue
{
set { SetValue(TestValueProperty, value); }
get
{
return (int)GetValue(TestValueProperty);
}
}
...
MyViewModel.cs
using System;
using System.Timers;
using Microsoft.Practices.Prism.ViewModel;
namespace TestBinding
{
class MyViewModel : NotificationObject
{
private int _VMTestValue;
private Timer timer;
private Random _random;
public MyViewModel()
{
_random=new Random();
timer=new Timer();
timer.Interval = 500;
timer.Elapsed += new ElapsedEventHandler(timer_Elapsed);
timer.Start();
}
void timer_Elapsed(object sender, ElapsedEventArgs e)
{
VMTestValue = _random.Next(10, 300);
}
public int VMTestValue
{
set
{
_VMTestValue = value;
this.RaisePropertyChanged(() => this.VMTestValue);
}
get { return _VMTestValue; }
}
}
}
MainWindow.cs
...
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
this.DataContext = new MyViewModel();
}
}
...
MainWindow.xaml
...
<TestBinding1:TestUserControl TestValue="{Binding VMTestValue}" />
<TextBlock VerticalAlignment="Bottom" Background="Blue" FontSize="20" Text="{Binding VMTestValue}" />
...
Why can not I go to the UserControl?

Answer 1

in addition to baboon i do this in my projects:
remove this.DataContext = this; and add the following to your xaml
<UserControl x:Class="TestBinding.TestUserControl"
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"
Background="Green"
d:DesignHeight="300" d:DesignWidth="300"
x:Name="uc">
<Grid>
<TextBlock Background="Gray" Margin="50" FontSize="18" Text="{Binding ElementName=uc,Path=TestValue}" />
<Rectangle Height="200" Width="{Binding ElementName=uc,Path=TestValue}" Fill="#FFFF1717" />
</Grid>
</UserControl>

Answer 2

You should let your UserControl inherit the DataContext:
public TestUserControl()
{
InitializeComponent();
//this.DataContext = this;
}
If you want to keep the DataContext of TestUserControl to itself, you can use RelativeSource:
<TestBinding1:TestUserControl TestValue="{Binding DataContext.VMTestValue, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Window}}" />
Or use ElementName, let's say your MainWindow is named mainWin :
<TestBinding1:TestUserControl TestValue="{Binding VMTestValue, ElementName=mainWin}" />