UWP: how to get the RightTapped GridView Item

问题

I have a GridView like below

<GridView
         SelectionMode="None"
         IsItemClickEnabled="True"
         IsRightTapEnabled="True"
         ItemsSource="{x:Bind SymbolItems}"
         ItemClick="SymbolGridView_ItemClick"
         RightTapped="SymbolGridView_RightTapped">
   <GridView.ItemTemplate>
       <DataTemplate x:DataType="data:SoundSymbolItem">
           <local:SymbolControl/>
       </DataTemplate>
   </GridView.ItemTemplate>
</GridView>

I have a ItemClick handler and I can get the clicked symbolItem successfully

    private void SymbolGridView_ItemClick(object sender, ItemClickEventArgs e)
    {
        var symbolItem = (SymbolItem)e.ClickedItem;
        MyMediaElement.Source = new Uri(this.BaseUri, symbolItem.SymbolAudio);
    }

Now, I want to do the similar thing for the RightTapped event, but it can't get the right tapped item.

    private void SymbolGridView_RightTapped(object sender, RightTappedRoutedEventArgs e)
    {
        SymbolItem symbolItem = (sender as GridViewItem).DataContext as SymbolItem;
        MyMediaElement.Source = new Uri(this.BaseUri, symbolItem.ExampleAudio);
    }

I model the answer in this question Get RightTapped GridViewItem to write my right tapped handler above, but it's not working. When I right click a gridview item, a NullReferenceException is triggered.

回答1:

You should set SelectionMode="Single"in gridview and set IsRightTapEnabled="True".

My model has a class Student:

public class Student : NotifyProperty
{
    public string Name
    {
        set
        {
            _name = value;
            OnPropertyChanged();
        }
        get
        {
            return _name;
        }
    }

    private string _name;
}

And my viewmodel has a List<Student>.

I set the list as gridview's source.

My gridview is

   <GridView x:Name="SymbolGridView"
     SelectionMode="Single"
     IsItemClickEnabled="True"
     IsRightTapEnabled="True"
     ItemsSource="{x:Bind View.Student}"
     ItemClick="SymbolGridView_OnItemClick"
     RightTapped="SymbolGridView_OnRightTapped">
        <GridView.ItemTemplate>
            <DataTemplate x:DataType="view:ViewModel">
                <TextBlock Text="{Binding Name}"></TextBlock>
                </DataTemplate>
        </GridView.ItemTemplate>
    </GridView>

The SymbolGridView_OnRightTapped have a OriginalSource that is TextBlock.But if your DataTemlpate is a Grid ,the OriginalSource is Grid.

We can use var student = (e.OriginalSource as TextBlock)?.DataContext as Student; to get the student.

The OriginalSource.DataContext is your selects item

But if you use the Grid,the OriginalSource may is ListViewItemPresenter.So the easy methor is use var student = (e.OriginalSource as FrameworkElement)?.DataContext as Student;

See: http://lindexi.oschina.io/lindexi/post/win10-uwp-%E5%8F%B3%E5%87%BB%E9%80%89%E6%8B%A9GridViewItem

回答2:

If the SymbolControl in your ItemTemplate is a bit more complex and the elements in it may have their own DataContexts you could get a reference to the parent ListViewItemPresenter using the following helper method and then cast the DataContext of this to your Symbol item:

private void SymbolGridView_RightTapped(object sender, RightTappedRoutedEventArgs e)
{
    ListViewItemPresenter lvi = e.OriginalSource as ListViewItemPresenter;
    if (lvi == null)
        lvi = FindParent<ListViewItemPresenter>(e.OriginalSource as DependencyObject);

    if (lvi != null)
    {
        SymbolItem clickedItem = lvi.DataContext as SymbolItem;
        if (clickedItem != null)
            MyMediaElement.Source = new Uri(this.BaseUri, symbolItem.ExampleAudio);
    }
}

private static T FindParent<T>(DependencyObject dependencyObject) where T : DependencyObject
{
    var parent = VisualTreeHelper.GetParent(dependencyObject);

    if (parent == null) return null;

    var parentT = parent as T;
    return parentT ?? FindParent<T>(parent);
}

来源：https://stackoverflow.com/questions/41196009/uwp-how-to-get-the-righttapped-gridview-item

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