數據綁定CoverFlow控件的選定項目屬性？

Question

我正在使用Coverflow control in Windows 8 C# XAML App。

我想將此控件的選定項屬性綁定到屬性，但沒有任何效果。以下是我使用的代碼讓我知道我在做什麼錯誤？

<controls:CoverFlow 
    Height="85" 
    Margin="0,40,0,0" 
    HorizontalAlignment="Stretch" 
    VerticalAlignment="Stretch" 
    SpaceBetweenItems="35" 
    SelectedItem="{Binding DiarySelectedItem.DiarySmileyId}" 
    SpaceBetweenSelectedItemAndItems="40" 
    ItemClick="ItemView_ItemClick" 
    ItemTemplate="{StaticResource 50ItemTemplate}" 
    ItemsSource="{Binding DiarySmileyIdOC}" 
    SelectedItemChanged="CoverFlow_SelectedItemChanged" /> 

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

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

     _diarySelectedItem = value; 
     RaisePropertyChanged(DiarySelectedItemPropertyName); 
    } 
} 

/// <summary> 
///  Gets or sets the Diary Smiley Id Observable Collection. 
/// </summary> 
/// <value> 
///  The Diary Smiley Id Observable Collection. 
/// </value> 
public ObservableCollection<int> DiarySmileyIdOC 
{ 
    get { return _diarySmileyIdOC; } 

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

     _diarySmileyIdOC = value; 

     // Update bindings, no broadcast 
     RaisePropertyChanged(DiarySmileyIdOCPropertyName); 
    } 
} 

Answer 1

既然你結合ObservableCollection<int>到ItemsSource，SelectedItem是int爲好。你已經考慮到了這一點，通過綁定到DiarySelectedItem.DiarySmileyId而不是直接到DiarySelecteditem。

這有一個副作用，雖然你並沒有真正改變DiarySelectedItem但只是試圖改變其DiarySmileyId財產的價值。這可能不是你想要的有以下幾個原因：

• 如果DiarySelectedItem是null，分配給DiarySelectedItem.DiarySmileyId時什麼都不會發生，因爲無聲NullReferenceException。
• 如果DiarySelectedItem不null和DiaryItemDetail.DiarySmileyId有一個公共的setter，分配給DiarySelectedItem會改變，而其他屬性保持不變DiarySmileyId財產的實例的值。
• 如果DiarySelectedItem不null和DiaryItemDetail.DiarySmileyId沒有一個公共的setter，會發生什麼，因爲DiarySmileyId不能分配給。

你應該有一個單獨的屬性DiarySelectedItemId達到預期的行爲：

public DiaryItemDetail DiarySelectedItemId 
{ 
    get { return _diarySelectedItem.DiarySmileyId; } 

    set 
    { 
     if (_diarySelectedItem.DiarySmileyId == value) 
     { 
      return; 
     } 

     DiarySelectedItem = GetDairyItemDetail(value); // retrieve instance from repository 
     RaisePropertyChanged(DiarySelectedItemIdPropertyName); 
    } 
} 

public DiaryItemDetail DiarySelectedItem 
{ 
    get { return _diarySelectedItem; } 

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

     _diarySelectedItem = value; 
     RaisePropertyChanged(DiarySelectedItemPropertyName); 
     // notification to change the selected item in Coverflow if selected item is changed in code 
     RaisePropertyChanged(DiarySelectedItemIdPropertyName); 
    } 
} 

爲什麼你不設置ObservableCollection<DiaryItemDetail>到ItemsSource，所以你可以直接綁定到SelectedItemSelectedItem？