在代码后面的依赖属性调用

Question

I have created a custom UserControl with some Dependency properties.
This custom control is hosted on a Window.
When I try to get a value from a DependecyProperty in code behind it doesn't work.

public static readonly DependencyProperty ValueDp = DependencyProperty.Register("Value", typeof(string), typeof(MyCustomUserControl), new FrameworkPropertyMetadata(string.Empty, OutputHandler));

public string Value
{
   get { return (string)GetValue(ValueDp); }
   set { SetValue(ValueDp, value); }
}

private static void OutputHandler(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
   var temp= dependencyObject as MyCustomUserControl;
   if (temp!= null)
   {
      dependencyObject.SetValue(ValueDp,temp._conversionValue);
   }
}

On the host I have put a button and when I click on it, I want to read the value stored in the DP, but I will always get the default value set in DP.

Any ideas what I`m doing wrong here?

Regards

Answer 1

我认为在OutputHandler方法中，您总是会丢弃分配给该属性的新值（ dependencyPropertyChangedEventArgs.NewValue ）

Answer 2

As @Alberto has said the OldValue and NewValue are the properties which hold the value of the DependencyProperty . The above properties are found in dependencyPropertyChangedEventArgs . In your Handler the member dependencyObject and temp refer to the same object.