WPF绑定变量/的DependencyProperty [英] WPF Binding to variable / DependencyProperty

问题描述

我在玩弄WPF绑定和变量。显然，一次只能绑定DependencyProperties。我想出了以下，这工作完全正常：
在code-隐藏文件：

I'm playing around with WPF Binding and variables. Apparently one can only bind DependencyProperties. I have come up with the following, which works perfectly fine: The code-behind file:

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    public string Test
    {
        get { return (string)this.GetValue(TestProperty); }
        set { this.SetValue(TestProperty, value); }
        //set { this.SetValue(TestProperty, "BBB"); }
    }
    public static readonly DependencyProperty TestProperty = DependencyProperty.Register(
      "Test", typeof(string), typeof(MainWindow), new PropertyMetadata("CCC"));

    private void button1_Click(object sender, RoutedEventArgs e)
    {
        MessageBox.Show(Test);
        Test = "AAA";
        MessageBox.Show(Test);
    }
}

XAML：

<Window x:Class="WpfApplication3.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:diag="clr-namespace:System.Diagnostics;assembly=WindowsBase"
    Title="MainWindow" Height="350" Width="525"
    DataContext="{Binding RelativeSource={RelativeSource Self}}">
<Grid>
    <TextBox Height="31" HorizontalAlignment="Left" Margin="84,86,0,0" Name="textBox1" VerticalAlignment="Top" Width="152" 
             Text="{Binding Test, Mode=TwoWay, diag:PresentationTraceSources.TraceLevel=High}"/>
    <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="320,85,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" />
    <TextBox Height="31" HorizontalAlignment="Left" Margin="84,138,0,0" Name="textBox2" Text="{Binding Test, Mode=TwoWay}" VerticalAlignment="Top" Width="152" />
</Grid>

在两个文本框更新一个一个其他。和按钮设置他们AAA。

The two TextBoxes update one an other. And the Button sets them to "AAA".

但现在我替换被注释掉（模拟给定值的一些处理）的一个二传手的功能。我希望，每当属性值被更改，将被重置为BBB。它这样做，当你preSS按钮，也就是说当你设置code中的财产。但它确实由于某些原因不影响WPF绑定，即你可以改变文本框内容，因此，财产，但显然二传手永远不会被调用。
我不知道为什么会这样，一会如何去才达到预期的行为。

But now I replaced the Setter function with the one that is commented out (simulating some manipulation of the given value). I would expect that whenever the property value is changed it will be reset to "BBB". It does so when you press the button, that is when you set the property in code. But it does for some reason not affect the WPF Bindings, that is you can change the TextBox contents and thus the property, but apparently the Setter is never called. I wonder why that is so, and how one would go about to achive the expected behaviour.

推荐答案

的CLR属性包装为一个依赖属性永远不会保证被调用，因此，你不应该把任何额外的逻辑在那里。当你需要额外的逻辑，当DP发生变化时，应使用性质改变的回调。

The CLR Property wrapper for a Dependency Property is never guaranteed to be called and therefore, you should never place any additional logic there. Whenever you need additional logic when a DP is changed, you should use the property changed callback.

在你的情况。

public string Test
{
    get { return (string)this.GetValue(TestProperty); }
    set { this.SetValue(TestProperty, value); }
}

public static readonly DependencyProperty TestProperty =
    DependencyProperty.Register("Test",
    typeof(string),
    typeof(MainWindow),
    new PropertyMetadata("CCC", TestPropertyChanged));

private static void TestPropertyChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
    MainWindow mainWindow = source as MainWindow;
    string newValue = e.NewValue as string;
    // Do additional logic
}

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