Observable.FromEvent 可以与 DataContextChanged 一起使用吗

发布于 2024-12-03 23:01:42 字数 469 浏览 1 评论 0原文

我想获取控件的 DataContext 作为 IObservable。我已经尝试过这个：

Observable.FromEvent<DependencyPropertyChangedEventHandler,
     DependencyPropertyChangedEventArgs>
     (a => this.DataContextChanged += a, a => this.DataContextChanged -= a)
     .Subscribe(e => MessageBox.Show(e.NewValue.ToString()));

它编译得很好，但是在调用 Subscribe 时它会抛出异常：绑定到目标方法时出错。

我的猜测是，这是因为 DependencyPropertyChangedEventArgs 不继承自事件参数，但我不确定。任何有关正确方法的建议将不胜感激。

原文

I want to get the DataContext of a control as an IObservable. I've tried this:

Observable.FromEvent<DependencyPropertyChangedEventHandler,
     DependencyPropertyChangedEventArgs>
     (a => this.DataContextChanged += a, a => this.DataContextChanged -= a)
     .Subscribe(e => MessageBox.Show(e.NewValue.ToString()));

Which compiles fine, but at the point where Subscribe is called it throws the exception: Error binding to target method.

My guess is that this is because DependencyPropertyChangedEventArgs doesn't inherit from event args, but I'm not sure. Any advice on the right way to do this would be apreciated.

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疏忽 2024-12-10 23:01:42

FromEvent 的其他重载之一允许您自己从方法创建委托。允许你这样做：

Observable.FromEvent
    <DependencyPropertyChangedEventHandler, DependencyPropertyChangedEventArgs>
    (a => new DependencyPropertyChangedEventHandler(
        new Action<object, DependencyPropertyChangedEventArgs>((s, e) => a(e))),
        h => this.DataContextChanged += h, h => this.DataContextChanged -= h)
        .Subscribe(e => MessageBox.Show(e.NewValue.ToString()));

这似乎有效

One of the other overloads for FromEvent allows you to create the delegate yourself from a method. Allowing you to do this:

Observable.FromEvent
    <DependencyPropertyChangedEventHandler, DependencyPropertyChangedEventArgs>
    (a => new DependencyPropertyChangedEventHandler(
        new Action<object, DependencyPropertyChangedEventArgs>((s, e) => a(e))),
        h => this.DataContextChanged += h, h => this.DataContextChanged -= h)
        .Subscribe(e => MessageBox.Show(e.NewValue.ToString()));

which seems to work

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活雷疯 2024-12-10 23:01:42

您已经“击中要害”了，由于某种原因 DependencyPropertyChangedEventArgs 是一个结构，因此不会继承 EventArgs。请参阅此相关博客文章：

http://weblogs.asp.net /okloeten/archive/2007/12/10/5430331.aspx

这使得无法使用通用事件处理机制来处理此事件。

我想您必须在自己的代码中处理此事件并手动创建一个 Observable 。

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紫﹏色ふ单纯 2024-12-10 23:01:42

自定义实现将非常简单：

Observable.CreateWithDisposable<DependencyPropertyChangedEventHandler>(obs =>
{
   var subject = new Subject<DependencyPropertyChangedEventHandler>();
   //Attach event handler and on event call OnNext of subject with the value
   return subject.Subscribe(obs);
});

更新：处理事件处理程序删除

public class GenericDisposable : IDisposable
        {
            Action _act = null;
            IDisposable _disp = null;
            public GenericDisposable(Action act,IDisposable disp)
            {
                _act = act;
                _disp = disp;
            }
            public void Dispose()
            {
                _act();
                _disp.Dispose();
            }
        }
        public static IObservable<DependencyPropertyChangedEventHandler> CreateForEvent()
        {
            return Observable.Defer(() =>
            {
                return Observable.CreateWithDisposable<DependencyPropertyChangedEventHandler>(obs =>
                {
                    var subject = new Subject<DependencyPropertyChangedEventHandler>();
                    //Attach event handler and on event call OnNext of subject with the value
                    return new GenericDisposable(() => {/*remove event handler*/}, subject.Subscribe(obs));
                });
            });
        }

The custom implementation would be as simple as:

Observable.CreateWithDisposable<DependencyPropertyChangedEventHandler>(obs =>
{
   var subject = new Subject<DependencyPropertyChangedEventHandler>();
   //Attach event handler and on event call OnNext of subject with the value
   return subject.Subscribe(obs);
});

UPDATED : To handle event handler removal

public class GenericDisposable : IDisposable
        {
            Action _act = null;
            IDisposable _disp = null;
            public GenericDisposable(Action act,IDisposable disp)
            {
                _act = act;
                _disp = disp;
            }
            public void Dispose()
            {
                _act();
                _disp.Dispose();
            }
        }
        public static IObservable<DependencyPropertyChangedEventHandler> CreateForEvent()
        {
            return Observable.Defer(() =>
            {
                return Observable.CreateWithDisposable<DependencyPropertyChangedEventHandler>(obs =>
                {
                    var subject = new Subject<DependencyPropertyChangedEventHandler>();
                    //Attach event handler and on event call OnNext of subject with the value
                    return new GenericDisposable(() => {/*remove event handler*/}, subject.Subscribe(obs));
                });
            });
        }

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