属性更改时引发事件

Question

I need to raise an event when the value of the property is changed. In my case this is when webView.Source is changed. I can't make a derived class because the class is marked as sealed. Is there any way to raise an event ?

Thank you.

Answer 1

Raise event when property is changed

For this scenario, you could create a DependencyPropertyWatcher to detect DependencyProperty changed event. The follow is tool class that you could use directly.

public class DependencyPropertyWatcher<T> : DependencyObject, IDisposable
{
    public static readonly DependencyProperty ValueProperty =
        DependencyProperty.Register(
            "Value",
            typeof(object),
            typeof(DependencyPropertyWatcher<T>),
            new PropertyMetadata(null, OnPropertyChanged));

    public event DependencyPropertyChangedEventHandler PropertyChanged;

    public DependencyPropertyWatcher(DependencyObject target, string propertyPath)
    {
        this.Target = target;
        BindingOperations.SetBinding(
            this,
            ValueProperty,
            new Binding() { Source = target, Path = new PropertyPath(propertyPath), Mode = BindingMode.OneWay });
    }

    public DependencyObject Target { get; private set; }

    public T Value
    {
        get { return (T)this.GetValue(ValueProperty); }
    }

    public static void OnPropertyChanged(object sender, DependencyPropertyChangedEventArgs args)
    {
        DependencyPropertyWatcher<T> source = (DependencyPropertyWatcher<T>)sender;

        if (source.PropertyChanged != null)
        {
            source.PropertyChanged(source.Target, args);
        }
    }

    public void Dispose()
    {
        this.ClearValue(ValueProperty);
    }
}

Usage

var watcher = new DependencyPropertyWatcher<string>(this.MyWebView, "Source");
watcher.PropertyChanged += Watcher_PropertyChanged;

private void Watcher_PropertyChanged(object sender, DependencyPropertyChangedEventArgs e)
{

}

Answer 2

您可以使用装饰器包装原始类，并为装饰的属性引发一个事件。