Question

I have the following code to subscribe to property changed event for VisiblePosition property of Column class:

DependencyPropertyDescriptor dpd = DependencyPropertyDescriptor.FromProperty(ColumnBase.VisiblePositionProperty, typeof(Column));

if (dpd != null)
{
   dpd.AddValueChanged(col, ColumnVisiblePositionChangedHandler);
}

Here is the definition of the ColumnVisiblePositionChangedHandler method:

static internal void ColumnVisiblePositionChangedHandler(object sender, EventArgs e)

问题是,我需要获得财产的旧价值。我如何这样做?

感谢

Answer 1

不幸的是,在登记财产时,你没有以这种方式改变活动手法。

一项工作是,在某个地方(这是你的旧价值)储存财产价值,然后将其与事件手里的现值相比较。

另一项工作是创造你们自己的依赖性财产,在阁下的住房和财产管理局与控制局之间形成约束力。这将使你能够以世界森林论坛的风格发出更改通知。

Here is an article about this.

Answer 2

当你在所附活动中登记其扶养财产时,你可以这样做。请见下文关于扶养财产的辛迪加,以及如何将旧价值列入<代码>。 PropertyChanged 活动手稿:

//Declaration of property
public static readonly DependencyProperty MyNameProperty =
    DependencyProperty.Register("MyName",
                                typeof(PropertyType),
                                typeof(ClassName),
                                new PropertyMetadata(null,
                                new PropertyChangedCallback(MyNameValueChanged)));

//PropertyChanged event handler to get the old value
private static void MyNameValueChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs eventArgs)
{
    object oldValue = eventArgs.OldValue; //Get the old value
}

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