Question

我在页面上显示时间/时钟作为用户控件（ClockControl），实际时间模型来自另一个类的DateTime对象（ClockTime ）。我在ClockControl上有2个文本块：

Textblock＆＃39; Second_update_by_binding＆＃39;绑定到依赖属性＆＃39; Second_binded＆＃39;反过来，它必然会模拟ClockTime＆＃39; Second＆＃39;
Textblock＆＃39; Second_update_by_manipulating＆＃39;通过操纵模型ClockTime＆＃39; Second＆＃39;的值来更新所以它增加了＆＃39; 0＆＃39;在前面如果＆＃39; Second＆＃39;只有1位数（或少于10位）

无论是最好的方法，我都能实现我的目标。但是，我遇到了一些问题，我不太明白为什么会这样。特别是，它是我最困惑的时钟用户控件中依赖属性内的getter / setter内部代码背后的逻辑。

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模型：

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(""));
    //==================================
}

所以这是我的问题：

为什么调试代码 Debug.WriteLine（＆＃34;在Second_binded＆＃34;中）; 在ClockControl中的Second_binded依赖属性的setter中，从不调用＆＃39 ;二＆＃39;在模型ClockTime正在更新。
调用ClockControl中Second_manipulated依赖属性的setter中的代码 Debug.WriteLine（＆＃34;在Second_manipulated＆＃34;中）; ，并且代码 Value_1。 Text =（Convert.ToInt32（value）＆lt; 10）？＆＃34; 0＆＃34; + value：value; 执行以更改ClockControl上的文本，但只有在MainPage.cs中添加另一个DispatchTimer以强制代码 useControl.Second_manipulated后才能执行此操作= clock.Second.ToString（）; 更新时间。为什么我必须以这种方式更新Second_manipulated，即使我已经在MainPage.xaml中将Second_manipulated绑定为Second？

非常欢迎任何能够启发我对C＃的了解的想法和评论。

感谢

肯

Answer 1

如果要跟踪DependencyProperty中的更改，则必须注册PropertyChangedCallback处理程序。更新绑定的值时，系统不会触发属性设置器。

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");
}

你的setter在第二个属性中命中的原因是因为你自己用useControl.Second_manipulated = clock.Second.ToString();强制它，这不是使用绑定的正确方法。

有关用户控件中DependencyProperty的setter中的代码的问题

1 个答案: