DependencyObject.InvalidateProperty不工作 [英] DependencyObject.InvalidateProperty not working

问题描述

根据在documentation通过MSDN ...

Based on the documentation via MSDN...

您也可以使用InvalidateProperty来
  有约束力的力量重新评估
  针对不能够将数据源
  实施建议
  INotifyPropertyChanged的通知
  机制...

You can also use InvalidateProperty to force re-evaluation of a binding against a data source that is not able to implement the recommended INotifyPropertyChanged notification mechanism...

...的code以下应该工作，但它没有。

...the code below should work, yet it doesn't.

public partial class Window1 : Window
{
    private Payload _payload = new Payload();

    public Window1()
    {
        InitializeComponent();

        this.DataContext = _payload;
    }

    private void Invalidate(object sender, RoutedEventArgs e)
    {
        _payload.Timestamp = DateTime.Now.Add(TimeSpan.FromHours(1)).ToLongTimeString();

        Button b = sender as Button;
        b.InvalidateProperty(Button.ContentProperty);
    }
}

public class Payload
{
    private String _payload = DateTime.Now.ToLongTimeString();
    public String Timestamp 
    {
        get
        {
            return _payload;
        }
        set
        {
            _payload = value;
        }
   }
}

<Grid>
    <Button Click="Invalidate"
            Width="100" 
            Height="50" 
            Content="{Binding Path=Timestamp}"/>
</Grid>

任何想法是什么原因造成这种现象？

Any idea what is causing this behavior?

推荐答案

正如你所提到的，它应该工作，但没有。但是有一个简单的解决方法：

As you mentioned, it ought to work but doesn't. But there is a simple workaround:

// Doesn't work:
//b.InvalidateProperty(Button.ContentProperty);

// Works:
BindingOperations.GetBindingExpression(b, Button.ContentProperty).UpdateTarget();

我调试到参考源和所有 InvalidateProperty 确实在你的情况是会导致缓存值从 BindingEx $ P重新读$ pssion 到按钮 内容属性。随口说说，我不知道什么时候这甚至是必要的，但它不是有用得到 BindingEx pression 来重新阅读的原始属性。

I debugged into the reference source and all InvalidateProperty does in your situation is cause a cached value to be re-read from the BindingExpression into the Button Content property. Offhand, I don't know when this would even be necessary but it's not useful to get the BindingExpression to re-read the raw property.

由于解决方法是方便，一般情况下，保证只有进一步努力是提交与微软的bug报告。

Since the workaround is convenient and general, the only further effort warranted is filing a bug report with Microsoft.

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