How to make context menu work for windows phone?

问题:

I am using ContextMenu from Windows Phone Control toolkit. Wondering how do I know which list item in the list is pressed? It seems I can know which context menu is selected but I have no way to know which list item is operated on. Please help. Thanks!

        <DataTemplate x:Key="ListItemTemplate">
            <StackPanel Grid.Column="1" VerticalAlignment="Top">
                <TextBlock Tag="{Binding Index}"  Text="{Binding SName}" TextWrapping="Wrap" Style="{StaticResource PhoneTextExtraLargeStyle}" />
              <toolkit:ContextMenuService.ContextMenu>
                <toolkit:ContextMenu>
                  <toolkit:MenuItem Header="Add to playlist" Click="Move_Click"/>
                </toolkit:ContextMenu>
              </toolkit:ContextMenuService.ContextMenu>
            </StackPanel>

        private void Move_Click(object sender, RoutedEventArgs e)
    {
        String name = (string)((MenuItem)sender).Header;
        // how to know which index of the item is targeted on
    }

回答1:

I would also recommend MVVM, but it can be simplified. No need to go to the extreme of having a ViewModel for every object. The key is to bind the command to the DataContext of your ItemsControl (eg ListBox).

Let's assume that your ItemTemplate is for a ListBox, the ListBox has it's ItemsSource property bound to your ViewModel. Your xaml would look like this:

<ListBox x:Name="SongsListBox" ItemsSource="{Binding Songs}">
    <ListBox.ItemTemplate>
        <DataTemplate >
            <StackPanel >
                <TextBlock Text="{Binding SName}" TextWrapping="Wrap" Style="{StaticResource PhoneTextExtraLargeStyle}" />
                <toolkit:ContextMenuService.ContextMenu>
                   <toolkit:ContextMenu>
                       <toolkit:MenuItem Header="Add to playlist" Command="{Binding DataContext.AddToPlaylistCommand, ElementName=SongsListBox}" CommandParameter="{Binding}"/>
                   </toolkit:ContextMenu>
                </toolkit:ContextMenuService.ContextMenu>
            </StackPanel>              
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

Your ViewModel, would then have the property Songs, that is a collection of your model object. It also has an ICommand AddToPlaylistCommand. As I've said before, my favorite implementation of ICommand is the DelegateCommand from the PNP team.

public class ViewModel : INotifyPropertyChanged
{
    public ViewModel()
    {
        Songs = new ObservableCollection<Songs>();
        AddToPlaylistCommand = new DelegateCommand<Song>(AddToPlaylist);
    }
    public ICollection<Songs> Songs { get; set; }
    public ICommand AddToPlaylistCommand  { get; private set; }

    private void AddToPlaylist(Song song)
    {
        // I have full access to my model!
        // add the item to the playlist
    }

    // Other stuff for INotifyPropertyChanged
}

回答2:

The answer is: MVVM. Don't use the event registration in code-behind rather have a command be invoked in the ViewModel. First, Instead of binding to a Data object, bind to a ViewModel (or a ViewModel representing a single list item if you're in a list). Then instead of using the Click event, have your ViewModel expose a Command that can be invoke directly on the databound VM.

Here's a simplified example from my United Nations News OSS WP7 app: (XAML, C#)

<DataTemplate x:Key="ArticleItemDataTemplate">
    <StackPanel>
        <toolkit:ContextMenuService.ContextMenu>
            <toolkit:ContextMenu>
                <toolkit:MenuItem Command="{Binding NavigateToArticle}" Header="read article"/>
                <toolkit:MenuItem Command="{Binding ShareViaEmail}" Header="share via email"/>
                <toolkit:MenuItem Command="{Binding ShareOnFacebook}" Header="share on facebook"/>
                <toolkit:MenuItem Command="{Binding ShareOnTwitter}" Header="share on twitter"/>
            </toolkit:ContextMenu>
        </toolkit:ContextMenuService.ContextMenu>
        <TextBlockText="{Binding Title}">
    </StackPanel>
</DataTemplate>

public ICommand ShareOnTwitter
{
    get
    {
        return new RelayCommand(() => 
            IoC.Get<ISocialShareService>().ShareOnTwitter(ShareableOnSocialNetwroks));
    }
}

public ICommand ShareOnFacebook
{
    get
    {
        return new RelayCommand(() =>
            IoC.Get<ISocialShareService>().ShareOnFacebook(ShareableOnSocialNetwroks));
    }
}

public ICommand ShareViaEmail
{
    get
    {
        return new RelayCommand(() =>
            IoC.Get<ISocialShareService>().ShareViaEmail(ShareableOnSocialNetwroks));
    }
}

And here's another simplified sample of that same idea used in my Neurons WP7 OSS project: (XAML, C#)

    <DataTemplate x:Key="YouTubeVideoItem">
        <Grid>
            <Button >
                <toolkit:ContextMenuService.ContextMenu>
                    <toolkit:ContextMenu IsZoomEnabled="False">
                        <toolkit:MenuItem Command="{Binding NavigateToVideo}" Header="play video" />
                        <toolkit:MenuItem Command="{Binding ViewInBrowser}" Header="open in browser" />
                        <toolkit:MenuItem Command="{Binding SendInEmail}" Header="share via email" />
                        <toolkit:MenuItem Command="{Binding FacebookInBrowser}" Header="share on facebook" />
                        <toolkit:MenuItem Command="{Binding TweetInBrowser}" Header="share on twitter" />
                    </toolkit:ContextMenu>
                </toolkit:ContextMenuService.ContextMenu>
                <Custom:Interaction.Triggers>
                    <Custom:EventTrigger EventName="Click">
                        <GalaSoft_MvvmLight_Command:EventToCommand Command="{Binding NavigateToVideo}"/>
                    </Custom:EventTrigger>
                </Custom:Interaction.Triggers>
                <StackPanel Orientation="Horizontal">
                    <Image Height="90" Source="{Binding ImageUrl}" />
                    <TextBlock Width="271" Text="{Binding Title}" />
                </StackPanel>
            </Button>
        </Grid>
    </DataTemplate>

    public ICommand ViewInBrowser
    {
        get
        {
            return new RelayCommand(() =>
                TaskInvoker.OpenWebBrowser(this.ExternalLink.OriginalString)
            );
        }
    }

    public ICommand TweetInBrowser
    {
        get
        {
            return new RelayCommand(() =>
                IoC.Get<IMessenger>().Send(new NavigateToMessage(PageSources.WebBrowser, TwitterUri)));
        }
    }

    public ICommand FacebookInBrowser
    {
        get
        {
            return new RelayCommand(() =>
                IoC.Get<IMessenger>().Send(new NavigateToMessage(PageSources.WebBrowser, FacebookUri)));
        }
    }