我在 WinForms 应用程序中使用 RxFramework。我正在尝试运行 Observable 异步并使用 CancellationDisposable 在用户单击按钮时取消操作。但它不工作!
假设我有一个带有 2 个按钮和一个 ProgressBar 的表单。 Button1_click 在新线程上订阅观察者。然后在取消操作后立即按下 Button2_click。为什么 cancel.Token.IsCancellationRequested 永远不会为真?
private IDisposable obs = null;
private void button1_Click(object sender, EventArgs e) {
var countObserver = Observable.Create(observer => {
var cancel = new CancellationDisposable();
if (!cancel.Token.IsCancellationRequested) {
//Step 1 of a long running process using lot of resources...
observer.OnNext(1);
}
if (!cancel.Token.IsCancellationRequested) {
//Step 2 of a long running process using lot of resources...
observer.OnNext(1);
}
if (!cancel.Token.IsCancellationRequested) {
//Step 3 of a long running process using lot of resources...
observer.OnNext(1);
}
observer.OnCompleted();
return cancel;
});
obs = countObserver
.ObserveOn(new ControlScheduler(this))
.SubscribeOn(Scheduler.ThreadPool)
.Subscribe(i => {
//Update a progress bar here...
});
}
private void button2_Click(object sender, EventArgs e) {
if (obs != null)
obs.Dispose();
}
之所以会这样,是因为您传递给 Observable.Create
的 lambda 不会返回 CancellationDisposable
直到它完成所有步骤。因此,操作顺序如下:
- 您调用
订阅
- UI线程 block
- hiện hữu
ThreadPool
线程上,执行进入lambda
CancellationDisposable
已创建
- 您多次检查取消并执行整个过程。在此期间,您的进度条会更新。
cancel
从 lambda 返回
- UI线程被释放,
obs
得到它的值
- 您点击
Button2
并调用 obs.Dispose
cancel
获取 cancel.Token.IsCancellationRequested=true
。但是什么都没有发生,因为一切都已经发生了。
固定代码如下:
private void button1_Click(object sender, EventArgs e) {
var countObserver = Observable.Create(observer => {
var cancel = new CancellationDisposable();
// Here's the magic: schedule the job in background and return quickly
var scheduledItem = Scheduler.ThreadPool.Schedule(() =>
{
if (!cancel.Token.IsCancellationRequested) {
//Step 1 of a long running process using lot of resources...
observer.OnNext(1);
}
if (!cancel.Token.IsCancellationRequested) {
//Step 2 of a long running process using lot of resources...
observer.OnNext(1);
}
if (!cancel.Token.IsCancellationRequested) {
//Step 3 of a long running process using lot of resources...
observer.OnNext(1);
}
observer.OnCompleted();
});
return new CompositeDisposable(cancel, scheduledItem);
});
obs = countObserver
.ObserveOn(new ControlScheduler(this))
.Subscribe(i => {
//Update a progress bar here...
});
}
Tôi là một lập trình viên xuất sắc, rất giỏi!