c# - 上下文菜单继续使用Mvvm获取错误的对象

Question

我正在制作winodws 8电话应用程序，并尝试从Windows Phone工具包中获得上下文菜单。

我一直在关注此tutorial，但不是使用列表框，而是使用WP8内置的长列表选择器

<DataTemplate x:Key="GroceryListItemTemplate">
    <StackPanel Grid.Column="1" Grid.Row="1">
        <TextBlock x:Name="tbName" TextWrapping="Wrap" Text="{Binding Name}" FontSize="32"/>
        <TextBlock x:Name="tbProductInfo" TextWrapping="Wrap" Text="{Binding ProductInfoLabel}" HorizontalAlignment="Left"/>
    </StackPanel>
    <toolkit:ContextMenuService.ContextMenu>
        <toolkit:ContextMenu>
            <toolkit:MenuItem Header="Edit" 
                    Command="{Binding GroceryItemsVm.EditGroceryItemCmd, Source={StaticResource Locator}}"
                    CommandParameter="{Binding}"/>
            <toolkit:MenuItem Header="Delete" Command="{Binding GroceryItemsVm.DeleteGroceryItemCmd, Source={StaticResource Locator}}"
                    CommandParameter="{Binding}"/>
        </toolkit:ContextMenu>
    </toolkit:ContextMenuService.ContextMenu>
</DataTemplate>

上面是我的代码的简写

这是我的列表选择器

<phone:LongListSelector IsGroupingEnabled="True" ItemsSource="{Binding GroceryItems}"    HideEmptyGroups="True" LayoutMode="List" Grid.Row="1">     
            <phone:LongListSelector.ItemTemplate>
                <StaticResource ResourceKey="GroceryListItemTemplate"/>
            </phone:LongListSelector.ItemTemplate>
</phone:LongListSelector>

这是我的MVVM代码

public class GroceryItemsVm : ViewModelBase
{

    public GroceryItemsVm()
    {


        if (IsInDesignMode)
        {


        }
        else
        {

            EditGroceryItemCmd = new RelayCommand<GroceryItem>(this.Edit);
            DeleteGroceryItemCmd = new RelayCommand<GroceryItem>(this.Delete);

            GroceryItems = // method that gets all items back as grouped.



        }
    }

      private List<Group<GroceryItem>> groceryItems = null;

            /// <summary>
            /// Sets and gets the GroceryItems property.
            /// Changes to that property's value raise the PropertyChanged event. 
            /// </summary>
            public List<Group<GroceryItem>> GroceryItems
            {
                get
                {
                    return groceryItems;
                }

                set
                {
                    if (groceryItems == value)
                    {
                        return;
                    }

                    RaisePropertyChanging(() => GroceryItems);
                    groceryItems = value;
                    RaisePropertyChanged(() => GroceryItems);
                }
            }




    private async void Delete(GroceryItem obj)
    {
       // trigged on context delete
    }

    private void Edit(GroceryItem obj)
    {
        // triggered on context edit
    }



    public RelayCommand<GroceryItem> EditGroceryItemCmd
    {
        get;
        private set;
    }

    public RelayCommand<GroceryItem> DeleteGroceryItemCmd
    {
        get;
        private set;
    }

}


    public class GroceryItem : ObservableObject
        {
            /// <summary>
            /// The <see cref="Name" /> property's name.
            /// </summary>
            public const string NamePropertyName = "Name";

            private string name = "";

            /// <summary>
            /// Sets and gets the Name property.
            /// Changes to that property's value raise the PropertyChanged event. 
            /// </summary>
            public string Name
            {
                get
                {
                    return name;
                }

                set
                {
                    if (name == value)
                    {
                        return;
                    }

                    RaisePropertyChanging(() => Name);
                    name = value;
                    RaisePropertyChanged(() => Name);
                }
            }
        }

现在，当我运行它时，它第一次起作用，无论我选择对其进行编辑的任何项目，都将得到正确的对象。但是，下一个对象将始终是相同的。选择完成后，它永远不会更改其选择。

编辑

这是一个例子。

https://onedrive.live.com/redir?resid=FAE864D71B4770C6!19080&authkey=!ACUC2xXmZLVD7fE&ithint=file%2c.zip

运行它

触发上下文菜单以显示“1”以上

点击编辑-注释对话框消息(会说1)

点击“返回按钮”

触发上下文菜单以显示“3”以上

点击编辑-注释对话框消息(将显示3)

我唯一能想到的就是覆盖我要访问的页面的后退按钮，而只需导航到该页面即可。这有点愚蠢，但这就是我能想到的。

  public partial class MvvmView1 : PhoneApplicationPage
    {
        // Constructor
        public MvvmView1()
        {
            InitializeComponent();

            // Sample code to localize the ApplicationBar
            //BuildLocalizedApplicationBar();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            NavigationService.GoBack();
        }


        protected override void OnBackKeyPress(CancelEventArgs e)
        {
            NavigationService.Navigate(new Uri("/MainPage.xaml", UriKind.Relative));
        }


    }

Answer 1

这是ContextMenu的常见问题。我已经尝试了一段时间，想出一个解决方案，四处寻找。您说过，单击一次永远不会正确。

请尝试以下操作:

将卸载的处理程序添加到您的contextmenu中，如下所示:

<DataTemplate x:Key="GroceryListItemTemplate">
    <StackPanel Grid.Column="1" Grid.Row="1">
        <TextBlock x:Name="tbName" TextWrapping="Wrap" Text="{Binding Name}" FontSize="32"/>
        <TextBlock x:Name="tbProductInfo" TextWrapping="Wrap" Text="{Binding ProductInfoLabel}" HorizontalAlignment="Left"/>
    </StackPanel>
    <toolkit:ContextMenuService.ContextMenu>
        <toolkit:ContextMenu ***Unloaded="ContextMenu_Unloaded"***>
            <toolkit:MenuItem Header="Edit" 
                    Command="{Binding GroceryItemsVm.EditGroceryItemCmd, Source={StaticResource Locator}}"
                    CommandParameter="{Binding}"/>
            <toolkit:MenuItem Header="Delete" Command="{Binding GroceryItemsVm.DeleteGroceryItemCmd, Source={StaticResource Locator}}"
                    CommandParameter="{Binding}"/>
        </toolkit:ContextMenu>
    </toolkit:ContextMenuService.ContextMenu>
</DataTemplate>

删除*我添加它们以强调更改。
然后，该处理程序的代码如下:

private void ContextMenu_Unloaded(object sender, RoutedEventArgs e)
{
    var conmen = (sender as ContextMenu);
    if (conmen != null)
        conmen.ClearValue(DataContextProperty);
}

让我知道这个是否奏效。