SelectionChanged事件後無法重置LongListSelector中Grid的可視狀態

Question

我實現了VisualStateManager以突出顯示LongListSelector中的選定項。

所選項目在SelectionChanged事件中突出顯示，但問題在於事件完全執行時，所選項目仍然突出顯示。即使我離開頁面並返回到原始頁面，該項目仍然突出顯示。如果我在SelectionChanged事件的末尾添加selector.SelectedItem = null;，它會再次檢查該方法，直至最終拋出Object reference not set to instance of an object異常。

如何將所選項目的視覺狀態重置爲Normal一旦沒有使用？

SelectionChanged事件：

private async void POIS_SelectionChanged(object sender, SelectionChangedEventArgs e) 
    { 
     List<CustomUserControl> userControlList = new List<CustomUserControl>(); 
     GetItemsRecursive<CustomUserControl>(PoiLongListSelector, ref userControlList); 

     //seleted 
     if(e.AddedItems.Count > 0 && e.AddedItems[0] != null) 
     { 
      foreach (CustomUserControl userControl in userControlList) 
      { 
       if (e.AddedItems[0].Equals(userControl.DataContext)) 
       { 
        VisualStateManager.GoToState(userControl, "Selected", true); 
       } 
      } 
     } 
     //Unselected 
     if (e.RemovedItems.Count > 0 && e.RemovedItems[0] != null) 
     { 
      foreach (CustomUserControl userControl in userControlList) 
      { 
       if (e.RemovedItems[0].Equals(userControl.DataContext)) 
       { 
        VisualStateManager.GoToState(userControl, "Normal", true); 
       } 
      } 
     } 

     LongListSelector selector = sender as LongListSelector; 
     PoiData ld = selector.SelectedItem as PoiData; 
     string navigateUrl = ""; 
     SystemTray.ProgressIndicator = new ProgressIndicator(); 
     SetProgressIndicator(true); 
     //CHECK IF RETURNING NULL 
     SystemTray.ProgressIndicator.Text = "Getting GPS data"; 
     GeoCoordinate coordinate = await GetLocation(ctsPoi.Token); 
     if (coordinate != null) 
     { 
      string passedUrl = GenerateUrl(coordinate, ld.Type); 
      if (passedUrl != null) 
      { 
       SystemTray.ProgressIndicator.Text = "Getting POI data"; 
       string jsonData = await GetJsonDataFromGoogle(passedUrl, ld.Type); 
       if (jsonData != null) 
       { 
        string url = SerializeJsonData(jsonData, ld.Type); 
        if (url != null) 
        { 
         SystemTray.ProgressIndicator.Text = "Done"; 
         navigateUrl = string.Format("/ViewDirection.xaml?serializedData={0}", url); 
        } 
       } 
      } 
     } 
     if(navigateUrl != "") 
      (Application.Current.RootVisual as PhoneApplicationFrame).Navigate(new Uri(navigateUrl, UriKind.RelativeOrAbsolute)); 
    } 

CustomUserControl它具有VisualStateManager XAML：

<Grid x:Name="LayoutRoot"> 

     <Grid Margin="0,0,0,15" Grid.Row="0"> 
     <Grid Name="MainGrid" Opacity="1" Visibility="Visible" > 
       <Grid.Background> 
        <SolidColorBrush> 
         <Color>#ff00bfff</Color> 
        </SolidColorBrush> 
       </Grid.Background> 

       <Grid.ColumnDefinitions> 
        <ColumnDefinition Width="65" /> 
        <ColumnDefinition Width="*" /> 
       </Grid.ColumnDefinitions> 

       <Grid Background="{StaticResource PhoneAccentBrush}" Grid.Column="0" Width="65" HorizontalAlignment="Left" 
         Height="65" Margin="0, 0, 0, 0"> 
       </Grid> 
       <Grid Grid.Column="1"> 
        <TextBlock Text="{Binding Title}" 
           FontSize="30" Margin="10,0,0,0" 
           VerticalAlignment="Center" 
           Foreground="White"/> 
       </Grid> 
      </Grid> 
      <ProgressBar x:Name="ATMBar" Visibility="Visible" 
         Opacity="0" 
              VerticalAlignment="Center" 
              Margin="0,0,0,0" 
              IsIndeterminate="True" 
              Style="{StaticResource CustomIndeterminateProgressBar}" /> 

     </Grid> 

    <VisualStateManager.VisualStateGroups> 
     <VisualStateGroup x:Name="CommonStates"> 
      <VisualState x:Name="Normal"/> 
      <VisualState x:Name="Selected"> 
       <Storyboard> 
        <DoubleAnimation Duration="0" To="0.2" Storyboard.TargetProperty="Opacity" 
               Storyboard.TargetName="MainGrid" /> 

        <DoubleAnimation Duration="0" To="1" Storyboard.TargetProperty="Opacity" 
               Storyboard.TargetName="ATMBar" /> 
       </Storyboard> 
      </VisualState> 
     </VisualStateGroup> 
    </VisualStateManager.VisualStateGroups> 
</Grid> 

LongListSelector XAML：

<phone:LongListSelector Name="PoiLongListSelector" Margin="12,-20,0,75" 
             ItemsSource="{Binding Poi.Items}" 
             SelectionChanged="POIS_SelectionChanged"> 
    <phone:LongListSelector.ItemTemplate> 
         <DataTemplate> 
          <myUserControl:CustomUserControl /> 
         </DataTemplate> 
    </phone:LongListSelector.ItemTemplate> 

</phone:LongListSelector> 

Answer 1

你爲什麼不嘗試不同的東西來突出元素？，你可以綁定一個bac kground的顏色屬性或類似的東西后選擇改變方法，如果你使用的mvvm模式，你應該有INotifypropertyChange，所以，它必須改變這個值爲其他綁定到該屬性