How do you bind a Button Command to a member metho

Question

I have a ListView in my MVVM WPF implementation, it has a DataTemplate with a button inside. The ListView is bound to a collection of complex objects in the ViewModel.

 <ListView ItemsSource="{Binding Path=ComplexObjects}"
          SelectedItem="{Binding Path=SelectedObject}"
          Width="Auto">
    <ListView.View>
        <GridView>
            <GridViewColumn Header="My Property">
                <GridViewColumn.CellTemplate>
                    <DataTemplate>
                        <StackPanel Margin="6,2,6,2">
                            <TextBlock Text="{Binding MyProperty}"/>
                        </StackPanel>
                    </DataTemplate>
                </GridViewColumn.CellTemplate>
    </GridViewColumn>
            <GridViewColumn Header="First Name">
                <GridViewColumn.CellTemplate>
                    <DataTemplate>
                        <StackPanel Margin="6,2,6,2">
                            <Button Command="{Binding ???}"/>
                        </StackPanel>
                    </DataTemplate>
                </GridViewColumn.CellTemplate>
            </GridViewColumn>
    </GridView>
</ListView.View>

All the text fields are bound with no problem, but can I bind the Button Command to a member method of the ComplexObject? If so is there any way to pass parameters?

I have a feeling I'm probably just evading using an ICommand.

Thanks.

Answer 1

Yes for Button you will need to use ICommand established in your ComplexObject:

<Button Command="{Binding Path = CommandName}"/>

If your method is in the View Model that holds the ComplexObjects collection name your control or window Me and use something like this:

<Button Command="{Binding ElementName=Me, Path=DataContext.CommandName}" />

You could use click or preview mouse down, but if you're wanting to bind the method in XAML, you would still need to route that event to a command. It's just easier to bind the command.

Answer 2

You could bind an ICommand on the ViewModel, passing the instance to invoke the method on as a parameter. The ViewModel can then call the appropriate method on the right ComplexObject.

For example:

<DataTemplate>
    <StackPanel Margin="6,2,6,2">
        <Button Command="{Binding DoSomethingCommand, RelativeSource={RelativeSource AncestorType={x:Type ViewModelType}, Mode=FindAncestor}" CommandParameter="{Binding}"/>
    </StackPanel>
</DataTemplate>

Then the viewmodel could look like so:

public ICommand DoSomethingCommand
{
    get { return new DelegateCommand<object>(DoSomething); }
}

private void DoSomething(object instance)
{
    var complexObject = instance as ComplexObject;
    if (complexObject != null)
        complexObject.SomeMethod();
}

Answer 3

If you really wanted to get crazy I suppose you could make your own button custom control with a dependency property that is a delegate, and you could then bind to a property that returns the same type of delegate. And then in your custom control class you could invoke the delegate when it gets clicked.

---

There is always the standard ICommand, if you go that route this is how...

<Button Command={Binding CommandProperty} />

Use Kent Boogaart's DelegateCommand class from his blog post. Then...

In the class you are binding to:

private ICommand _commandField;

public ICommand CommandProperty
{
  get
  {
    if (_commandField == null) _commandField = new DelegateCommand(CommandMethod);

    return _commandField;
  }
}

private void CommandMethod() 
{
  // do stuff...
}