WPF 绑定到变量/DependencyProperty [英] WPF Binding to variable / DependencyProperty

问题描述

我正在研究 WPF 绑定和变量.显然只能绑定 DependencyProperties.我想出了以下内容，效果很好:代码隐藏文件:

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>

两个文本框相互更新.按钮将它们设置为AAA".

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

但现在我用注释掉的函数替换了 Setter 函数(模拟对给定值的一些操作).我希望每当属性值更改时，它都会重置为BBB".当您按下按钮时，即在代码中设置属性时，它就会这样做.但出于某种原因，它确实不会影响 WPF 绑定，也就是说，您可以更改 TextBox 内容，从而更改属性，但显然从未调用过 Setter.我想知道为什么会这样，以及如何实现预期的行为.

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

从不保证会调用依赖属性的 CLR 属性包装器，因此，您不应在其中放置任何额外的逻辑.每当您在更改 DP 时需要额外的逻辑时，您应该使用属性更改回调.

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.

就你而言..

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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