WPF ItemsControl Button command binding not working

Question

I have an ItemsControl control that has an ObservableCollection as its ItemsSource. It also has a button located inside of its DataTemplate. The button's Command property is bound to a RelayCommand in the ViewModel (I'm using MVVM Light) and the CommandParameter is bound to the corresponding item in the ItemsSource.
The problem is that the command never fires, for some reason. Code-behind works fine, on the other hand. When debugging the mouse click event handler I can see that the sender (of type Button) has a CommandParameter filled with the correct data whereas Command is null.

What did I miss here?

XAML:

<ItemsControl ItemsSource="{Binding Users}"
              Margin="{StaticResource ContentMargin}">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <WrapPanel Orientation="Horizontal" />
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Button Margin="{StaticResource ImageButtonMargin}"
                    Style="{StaticResource ImageButtonStyle}"
                    Command="{Binding RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}, Path=DataContext.UserSelectedCommand}"
                    CommandParameter="{Binding}">
                    <!--...-->

ViewModel:

private ObservableCollection<User> _users;
private RelayCommand<User> _userSelectedCommand;

public ObservableCollection<User> Users
{
    get { return _users; }
    set
    {
        _users = value;
        RaisePropertyChanged();
    }
}

public RelayCommand<User> UserSelectedCommand
{
    get { return _userSelectedCommand; }
}

protected override sealed void SetCommands() // called in the constructor which is in turned called by SimpleIoc
{
     userSelectedCommand = new RelayCommand<User>((user) => UserSeriesSelected(user));
}

private void UserSelected(User selectedUser)
{

}

loopedcode · Accepted Answer · 2015-09-12 19:18:52Z

23

Use named Element binding as binding source inside your data template to access commands from root data context. You can use root grid or other containers as named element. ItemsControl iteself can be used too.

<ItemsControl x:Name="MyItems" ItemsSource="{Binding Users}"
              Margin="{StaticResource ContentMargin}">
    <ItemsControl.ItemsPanel>
        <ItemsPanelTemplate>
            <WrapPanel Orientation="Horizontal" />
        </ItemsPanelTemplate>
    </ItemsControl.ItemsPanel>
    <ItemsControl.ItemTemplate>
        <DataTemplate>
            <Button Margin="{StaticResource ImageButtonMargin}"
                    Style="{StaticResource ImageButtonStyle}"
                    Command="{Binding ElementName=MyItems,  Path=DataContext.UserSelectedCommand}"
                    CommandParameter="{Binding}">
                    <!--...-->

answered Sep 12, 2015 at 19:18

loopedcode

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1 Comment

Vidar Over a year ago

I tried this and it worked - but I don't know why you have to set the ElementName to the name of the ItemsControl name, and why you have to specify Path=DataContext.FOO_COMMAND. Can anyone help to explain this?

Mikhail Karpov · Accepted Answer · 2015-09-12 19:13:46Z

7

You need to add "FindAncestor" to your relative source binding: RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ItemsControl}}

edited Sep 12, 2015 at 19:13

answered Sep 12, 2015 at 19:05

Mikhail Karpov

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Comments

Mattia Magosso · Accepted Answer · 2015-09-12 18:51:35Z

-2

In my opinion you should change your strategy, put the command in the User class and from that class notify the view-model through an event. This is going to simplify your xaml code and, in my opinion, making your view-model more coherent.

answered Sep 12, 2015 at 18:51

Mattia Magosso

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2 Comments

B.K. Over a year ago

That's a bad idea. User, which is a Model should not be handling commands.

Mattia Magosso Over a year ago

In this case just wrap the user with a view-model

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