problem with wpf command not executing when button clicked

c# wpf xaml binding

19,057

Looks like you are setting the DataContext of the Grid to the Data property of your ViewModel (or object). If the object that the Data property exposes doesn't provide the SaveData command, you'll have the problem you're describing. Remember the DataContext is inherited from the parent.

If you require that the DataContext is set in that manner, and still require the button to reference the parent DataContext, one option would be to use a RelativeSource to point to an element that has the ViewModel as the DataContext.

In WPF you also have the option of making those commands static and using the {x:Static} markup extension to reach it.

Hope that helps.

EDIT: Here's an example if your <Grid> is contained in a <UserControl>.

<Button Command="{Binding Path=DataContext.SaveData, 
                          RelativeSource={RelativeSource Mode=FindAncestor, 
                                          AncestorType={x:Type UserControl}}}" ... />

Also, I don't know what your full XAML looks like, but I suspect that this can be simplified greatly by removing the DataContext on the Grid and Binding Data on the ItemsControl (or whatever you're using to show the list of objects).

19,057

Author by

czuroski

MCSD .Net Framework 4.5 | Web Applications MCTS: MOSS 2007 Setup and Administration

Updated on June 08, 2022

Comments

czuroski almost 2 years

I have the following XAML in a WPF application. I would like to bind the button to an ICommand in a view model. For some reason, I am not able to see the command from my view. this is in a user control.

<Grid>
<Grid.DataContext>
        <Binding 
            x:Name="SettingsData"
            Path="Data" />
    </Grid.DataContext>
.
.
.
<DockPanel Grid.Column="1">
            <Button x:Name="SaveButton" 
                    DockPanel.Dock="Top"  
                    Height="25"  
                    HorizontalAlignment="Left" 
                    Margin="70 0 0 0"
                    Command="{Binding Path=SaveData}"

                    >Save Changes</Button>
        </DockPanel>
</Grid>

Here is my ICommand object -

public ICommand SaveData
{
    get
    {
        if (_saveData == null)
        {
            _saveData = new RelayCommand(
                param => this.saveData(),
                param => true
                );
        }
        return _saveData ;
    }
}

Does anyone have any idea why I cannot bind to this command?

Thanks for any thoughts....

czuroski almost 13 years

should I set the source to the name of the viewmodel?
Bek Raupov almost 13 years

i usually set the DataContext in code behind. How are u setting your View's DataContext?
czuroski almost 13 years

I set it in the xaml of the view at the grid level as shown above
czuroski almost 13 years

The savedata command does reside in the same viewmodel that the grid is bound to. Shouldn't it be able to see it?
SergioL almost 13 years

No, the DataContext of the Button is ViewModel.Data, not ViewModel. So, you're trying to bind to ViewModel.Data.SaveData. (And from your error, it seems like Data is a List of some object).
czuroski almost 13 years

So do I have to set the datacontext of the button to the viewmodel?
SergioL almost 13 years

Yes. But there are methods for getting it without explicitly setting it Xaml or code, including using RelativeSource or ElementName to point to a UIElement that already has the DataContext set to the ViewModel (most likely, the parent of Grid).
czuroski almost 13 years

The parent of the grid is the actual usercontrol. If I set the elementname to that, I still get an error.
czuroski almost 13 years

If I remove the datacontext from the grid as you mentioned above and put it at the list level, it works perfectly. Thank you for the help.
Ehsan Sajjad almost 7 years

thanks! i was having hard time from last couple of hours.