關於用戶控件中DependencyProperty的setter中代碼的問題

Question

我在頁面上顯示時間/時鐘作爲用戶控件（ClockControl），實際時間模型是從另一個類的DateTime對象驅動的（ ClockTime）。我對ClockControl 2周的TextBlocks：

1. 文字塊「Second_update_by_binding」勢必又被綁定到模型ClockTime「二」依賴屬性「Second_binded」。

2. 正文塊「Second_update_by_manipulating」由操縱模型ClockTime「第二」，使得它增加了的值來更新「0」，在前面，如果「第二」僅是1位（或小於10）

我設法實現我想要的，不管它是否是最好的方法。但是，我遇到了幾個我不太明白爲什麼會發生的問題。具體來說，它是時鐘用戶控件中依賴項屬性中getter/setter內部代碼的邏輯，這是我最困惑的。

MainPage.xaml中：

<Page x:Class="App1.MainPage" ..."> 
    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"> 
     <local:ClockControl x:Name="useControl" 
       Second_binded="{Binding Second}" 
       Second_manipulated="{Binding Second}" /> 
    </Grid> 
</Page> 

MainPage.cs：

public sealed partial class MainPage : Page 
{ 
    ClockTime clock; 
    DispatcherTimer Timer; 

    public MainPage() 
    { 
     clock = new ClockTime(); 
     this.InitializeComponent(); 
     this.DataContext = clock; 
      // I am adding this DispatchTimer to force the update of the text 
      // 'Second_update_by_manipulating' on the ClockControl since the 
      // Binding of Second_manipulated doesnt work 
     Timer = new DispatcherTimer { Interval = new TimeSpan(0, 0, 1) }; 
     Timer.Tick += Timer_Tick; 
     Timer.Start(); 
    } 

    private void Timer_Tick(object sender, object e) 
    { 
     useControl.Second_manipulated = clock.Second.ToString(); 
    } 
} 

ClockTime型號：

class ClockTime : INotifyPropertyChanged 
{ 
    public ClockTime() 
    { 
     var Timer = new DispatcherTimer { Interval = new TimeSpan(0, 0, 1) }; 
     Timer.Tick += Timer_Tick; 
     Timer.Start(); 
    } 

    private void Timer_Tick(object sender, object e) 
    { 
     Second = DateTime.Now.Second; 
    } 

    //=================================================== 
    public event PropertyChangedEventHandler PropertyChanged; 
    private void NotifyPropertyChanged(String info) 
    { 
     if (PropertyChanged != null) 
     { 
      PropertyChanged(this, new PropertyChangedEventArgs(info)); 
     } 
    } 
    //=================================================== 
    private int _second; 
    public int Second 
    { 
     get { return this._second; } 
     set 
     { 
      if (value != this._second) 
      { 
       this._second = value; 
       NotifyPropertyChanged("Second"); 
      } 
     } 
    } 
} 

ClockControl.xaml：

<UserControl x:Class="App1.ClockControl" ...> 
    <Grid> 
     <StackPanel> 
      <TextBlock x:Name="Second_update_by_manipulating" /> 
      <TextBlock x:Name="Second_update_by_binding" Text="{Binding Second_binded}" /> 
     </StackPanel> 
    </Grid> 
</UserControl> 

ClockControl.cs：

public sealed partial class ClockControl : UserControl 
{ 
    public ClockControl() 
    { 
     this.InitializeComponent(); 
     (this.Content as FrameworkElement).DataContext = this; 
    } 
    //================================== 
    public String Second_binded 
    { 
     get { 
      return (String)GetValue(Second_bindedProperty); 
     } 
     set { 
      Debug.WriteLine(" in Second_binded "); 
      SetValue(Second_bindedProperty, value); 
     } 
    } 
    public static readonly DependencyProperty Second_bindedProperty = 
     DependencyProperty.Register(
     "Second_binded", 
     typeof(string), 
     typeof(ClockControl), 
     new PropertyMetadata("")); 
    //================================== 
    public String Second_manipulated 
    { 
     get 
     { 
      return (String)GetValue(Second_manipulatedProperty); 
     } 
     set 
     { 
      Second_update_by_manipulating.Text = (Convert.ToInt32(value)<10) ? "0"+value : value; 
      Debug.WriteLine(" in Second_manipulated "); 
      SetValue(Second_manipulatedProperty, value); 
     } 
    } 
    public static readonly DependencyProperty Second_manipulatedProperty = 
     DependencyProperty.Register(
     "Second_manipulated", 
     typeof(string), 
     typeof(ClockControl), 
     new PropertyMetadata("")); 
    //================================== 
} 

所以這裏是我的問題：

1. 爲什麼調試代碼的Debug.WriteLine（ 「在Second_binded」）;在模型ClockTime中的'Second'正在更新時，ClockControl中的Second_binded依賴項屬性的setter中的永遠不會被調用。

2. 代碼Debug.WriteLine（「in Second_manipulated」）; ClockControl中的Second_manipulated依賴項屬性的setter被調用且代碼Value_1.Text =（Convert.ToInt32（value）< 10）？ 「0」+ value：value;執行以更改ClockControl上的文本，但僅在添加另一個DispatchTimer並使用MainPage.cs強制執行代碼後才起作用useControl.Second_manipulated = clock.Second.ToString（）;更新時間。爲什麼我必須這樣做來更新Second_manipulated，即使我已經在MainPage.xaml中將Second_manipulated綁定爲Second了？

任何想法和意見，啓發我的知識在C＃非常受歡迎。

感謝

肯

Answer 1

如果你想跟蹤一個DependencyProperty變化，你必須註冊一個PropertyChangedCallback處理。更新綁定的值時，系統不會觸發屬性設置器。

public static readonly DependencyProperty Second_bindedProperty = 
     DependencyProperty.Register(
     "Second_binded", 
     typeof(string), 
     typeof(ClockControl), 
     new PropertyMetadata("", PropertyChangedCallback)); 

private static void PropertyChangedCallback(DependencyObject dependencyObject, 
      DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs) 
{ 
    Debug.WriteLine(" in Second_binded callback"); 
} 

之所以你的二傳手被擊中的第二個屬性是因爲你強迫自己將其與useControl.Second_manipulated = clock.Second.ToString();，這是不使用綁定的正確途徑。