windows-phone-7 - 隐藏空的上下文菜单

Question

我在 wp7 中有一个上下文菜单

<toolkit:ContextMenuService.ContextMenu>
    <toolkit:ContextMenu x:Name="onHoldContextMenu">
        <toolkit:MenuItem Header="Delete" Tag="{Binding}" Click="DeleteVisitorNote_Click" Visibility="{Binding DeleteContextVisibility, Converter={StaticResource BooleanToVisibilityConverter}}"/>
        <toolkit:MenuItem Header="View" Tag="{Binding}" Visibility="{Binding ViewContextVisibility, Converter={StaticResource BooleanToVisibilityConverter}}" Click="ViewVisitorContact_Click"/>
    </toolkit:ContextMenu>
</toolkit:ContextMenuService.ContextMenu>

我正在更改 View 模型中两个项目的可见性，它工作正常。我的问题是，当我将这两个项目的可见性设置为 false 时，打开上下文菜单时我有一条空白的白线，而且我不知道如何隐藏它...我试过:

<toolkit:ContextMenuService.ContextMenu>
    <toolkit:ContextMenu x:Name="onHoldContextMenu"  Visibility="{Binding ContextVisibility, Converter={StaticResource BooleanToVisibilityConverter}}">
        <toolkit:MenuItem Header="Delete" Tag="{Binding}" Click="DeleteVisitorNote_Click" Visibility="{Binding DeleteContextVisibility, Converter={StaticResource BooleanToVisibilityConverter}}"/>
        <toolkit:MenuItem Header="View" Tag="{Binding}" Visibility="{Binding ViewContextVisibility, Converter={StaticResource BooleanToVisibilityConverter}}" Click="ViewVisitorContact_Click"/>
    </toolkit:ContextMenu>
</toolkit:ContextMenuService.ContextMenu>

但在这种情况下，我得到一个 nullreference 异常......

当上下文菜单为空时如何隐藏它？

Answer 1

我在另一个论坛上找到了这个解决方案。

        <ListBox.ItemTemplate> 
                <DataTemplate> 
                    <Grid Hold="Grid_Hold"> 
                        <toolkit:ContextMenuService.ContextMenu> 
                            ... context menu items ... 
                        </toolkit:ContextMenuService.ContextMenu> 

                        ... listbox item contents ... 

                    </Grid> 
                </DataTemplate> 
            </ListBox.ItemTemplate> 

    private void Grid_Hold(object sender, System.Windows.Input.GestureEventArgs e) 
    { 
        ItemViewModel listitem = (sender as FrameworkElement).DataContext as ItemViewModel; 
        e.Handled = listitem.DisableContextMenu(); 
    } 

设置 e.Handled = true 会阻止 ContextMenu 接收 Hold 事件。在您的 View 模型中，您将实现一些返回是否显示 ContextMenu 的属性或方法。