xaml - Windows Phone 工具包 ListPicker 引发未处理的异常

Question

我正在开发一个 Windows Phone 8 应用程序。我的应用程序使用来自 Tookit 的 ListPicker。我有问题的代码如下所示:

<toolkit:ListPicker x:Name="myListPicker" Margin="12,-6,12,-2" Loaded="myListPicker_Loaded">
  <toolkit:ListPicker.Items>
    <!-- Items are defined here -->
  </toolkit:ListPicker.Items>
</toolkit:ListPicker>


private void myListPicker_Loaded(object sender, RoutedEventArgs e)
{
  if ((myListPicker != null) && (viewModel != null))
  {

  }
}

每当项目总数超过某个阈值时，我的应用程序就会引发 System.ArgumentException。我知道这一点，因为我有以下代码:

    private void Application_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e)
    {
        MessageBox.Show(e.ExceptionObject.Message + "\n\nException\n" + e.ExceptionObject.GetType().FullName + "\n" + e.ExceptionObject.StackTrace);
        if (Debugger.IsAttached)
        {
            // An unhandled exception has occurred; break into the debugger
            Debugger.Break();
        }
    }

消息显示“值不在预期范围内。”。据我所知，当 ListPicker 需要进入全屏模式时会发生这种情况。我无法弄清楚为什么会发生这种情况。

有没有人有任何见解？

Answer 1

看起来，在全屏模式下，您无法将 ListPicker 的项目设置为 xaml 页面中的特定 UI 元素。您必须绑定(bind)它们或使用模板。
在遇到这个确切的问题后，我在这里找到了一个解释:http://silverlight.codeplex.com/workitem/9412

ListPickerItems are UIElements, and the ListPicker renders them in its presenter. When there are 5 or less items, the expanded mode opens on the current page, and you can see all the items in the presenter. When 6 or more items are present, opening the list picker goes to full mode which opens a new page. This new page has a listbox, which gets its items property set to the listpicker's items. This is where it breaks. By setting the listbox's items to the listpicker's items (in this case a list of listpickeritems), the listbox will put those UIElements into its view. Now a single listboxitem is included in two places on the visual tree.

Because of this issue, ListPicker only supports databinding and templating. DO NOT set the ListPicker's items to specific UIElements.

我设法让我的解决方案做这样的事情:

<toolkit:ListPicker x:Name="myListPicker" Margin="12,-6,12,-2" Loaded="myListPicker_Loaded">
  <toolkit:ListPicker.ItemTemplate>
      <DataTemplate>
          <TextBlock Text="{Binding Name}" Tag="{Binding ID}"/>
      </DataTemplate>
   </toolkit:ListPicker.ItemTemplate>
   <toolkit:ListPicker.FullModeItemTemplate>
      <DataTemplate>
          <TextBlock Text="{Binding Name}" Tag="{Binding ID}"/>
      </DataTemplate>
   </toolkit:ListPicker.FullModeItemTemplate>
</toolkit:ListPicker>


private void myListPicker_Loaded(object sender, RoutedEventArgs e)
{
  if ((myListPicker != null) && (viewModel != null))
  {
     myListPicker.ItemsSource = _Data; //_data is an array of objects with 2 properties named ID & Name
  }
}