What is wrong with this WPF binding?

Question

The instance of the class is a private member of the view code exposed as a public property named "ViewModel".

Without looking, I can definitely say, "I don't know." But I do know who does know--Snoop. Get it and use it to debug your bindings at runtime. — , Apr 23 '15 at 17:04

score 2 · Answer 1 · edited May 23 '17 at 12:23

2

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?

edited May 23 '17 at 12:23

Community

1
1

answered Apr 23 '15 at 14:38

Rachel

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Thank you, Rachel! Is this what you mean? – Justin McCarthy Apr 23 '15 at 14:58
If you bind the `ViewModel` property, be sure the parent's DataContext is set to an object that contains the `.ViewModel` property. Typically I will set my application's .DataContext in the code behind (something like `MyApplicationWindow.DataContext = new ApplicationViewModel();`), and have everything else use bindings or implicit data templates to inherit their .DataContext from there. The solution [posted by octavioccl](http://stackoverflow.com/a/29826915/302677) would also work, although I personally prefer to avoid defining the data context as a static resource in the XAML like that – Rachel Apr 23 '15 at 15:03
Thank you, Rachel. I think I prefer to have an instance of the ViewModel DataSource in the code behind as well. – Justin McCarthy Apr 23 '15 at 15:13

ocuenca · Answer 2 · 2015-04-23T15:04:27.083

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>

What is wrong with this WPF binding?

2 Answers2