WPF ComboBox SelectionChanged event to command not firing

8
votes

I have the following XAML of a ComboBox which has a code-behind SelectionChanged event handler and another Command property of the ViewModel. I have set the SelectedIndex property to 0. Now when I run the project, the code-behind handler is invoked, but the Command is not executed. What I want is that the Command should be executed for SelectedIndex=0 the first time the View is loaded.

<ComboBox Name="listComboBox" SelectionChanged="listComboBox_SelectionChanged" SelectedIndex="0" SelectedValuePath="Content" Margin="5,0" Height="35" Width="150" VerticalAlignment="Center" HorizontalAlignment="Left">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="SelectionChanged">
            <i:InvokeCommandAction Command="{Binding ListTypeComboSelectionChangedCmd}" CommandParameter="{Binding ElementName=listComboBox, Path=SelectedValue}"/>
        </i:EventTrigger>
     </i:Interaction.Triggers>
     <ComboBoxItem Content="ItemOne" />
     <ComboBoxItem Content="ItemTwo" />
     <ComboBoxItem Content="ItemThree" />
</ComboBox>

Update

Code-behind event handler:

private void listComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e) { }

ICommand object:

public ICommand ListTypeComboSelectionChangedCmd 
{ 
    get { return new RelayCommand<string>(ListTypeComboSelectionChangedCmdExec); }
    private set;
}

ICommand Handler:

private void ListTypeComboSelectionChangedCmdExec(string listType) { }
2
wpfmvvmcombobox
Why is this for? If you want something to happen just after the view as loaded why not do it when in loads? Also, no event will be fired for a SelectedIndex set in xaml at creation (not runtime). – Xavier Huppé
You have an event and a command for the same thing. Get rid of the inline event call. – Xcalibur37
@Sinity, if the selectionchanged event for the first ComboBoxItem is fired right after the view is loaded, then why shouldn't the command execute ? – Lucifer
@Xcalibur37, even after I remove the SelectionChanged event handler the command does not execute. – Lucifer
@Lucifer, if so, post the code which fire the event you're talking about (after the view as loaded). – Xavier Huppé

2 Answers

7
votes

Bind SelectedValue to a Property on the view model.

In the Property set{...} block do your logic there or call 

ListTypeComboSelectionChangedCmdExec(value)

See Binding ComboBox SelectedItem using MVVM

3
votes

In my case, I use handler in the code behind and connect it to ModelView as below.

var viewModel = (MyViewModel)DataContext;
if (viewModel.MyCommand.CanExecute(null))
    viewModel.MyCommand.Execute(null);

Please check this link: Call Command from Code Behind