Question

I’m having problems setting the DataContext for all fields that are inside a stackPanel. What I would like to do is set the Data Context as vm:ViewModel. But it’s not working and when I ask VS for assistance with DataBinding it Displays the TextBox.DataContext inside the TextBox. Is there a way to only set it once or do I have to set it for each control?

    <StackPanel DataContext="vm:ViewModel">
    <TextBox Text="{Binding FirstNumber}" HorizontalAlignment="Left" Height="23" Margin="206,45,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120">
            <TextBox.DataContext>
                <vm:ViewModel/>
            </TextBox.DataContext>
        </TextBox>
    </StackPanel>

Answer 1

You need to get your DataContext to refer to an instance of your ViewModel.

DataContext="vm:ViewModel" is not creating an instance of the ViewModel…it’s just setting a string.

Use Property Element syntax instead:

    <StackPanel>
    <StackPanel.DataContext>
        <vm:ViewModel/>
    </StackPanel.DataContext>
    <TextBox Text="{Binding FirstNumber}" HorizontalAlignment="Left" Height="23" Margin="206,45,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
    </StackPanel>

And if you do that, then there’s no need/in fact it’s probably wrong to create another one in your TextBox.DataContext…you just want to inherit the DataContext of the StackPanel.

I’ll just show you another way to create a ViewModel and to refer to the instance of it so you have a bigger picture…..that is to create it in resources, and then refer to that resource in the binding…here’s an example:

<Window x:Class="WpfApplication8.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="clr-namespace:WpfApplication8"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <vm:ViewModel x:Key="myviewmodel"/>
    </Window.Resources>
        <StackPanel x:Name="stackp" DataContext="vm:ViewModel">
        <TextBox Text="{Binding Source={StaticResource myviewmodel}, Path=FirstNumber}" HorizontalAlignment="Left" Height="23" Margin="206,45,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
    </StackPanel>
</Window>

Another example that sets the DataContext at a higher level in the tree:

<Window x:Class="WpfApplication8.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="clr-namespace:WpfApplication8"
        Title="MainWindow" Height="350" Width="525">
    <Window.DataContext>
        <vm:ViewModel/>
    </Window.DataContext>
    <StackPanel>
        <TextBox Text="{Binding FirstNumber}" HorizontalAlignment="Left" Height="23" Margin="206,45,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="120"/>
    </StackPanel>
</Window>