当在工作线程上调用的方法需要在 UI 线程上运行代码并等待其完成后再执行其他操作时,可以这样做:
public int RunOnUi(Func<int> f)
{
int res = Application.Current.Dispatcher.Invoke(f);
return res;
}
但是如果我想用任务来做呢?有没有办法让 RunOnUi 方法创建一个在 UI 上启动的任务并返回它,以便调用者(在工作线程上运行)可以等待它?符合以下签名的东西:
public Task<int> StartOnUi(Func<int> f)
?
一种方法如下:
public Task<int> RunOnUi(Func<int> f)
{
var task = new Task<int>(f);
task.Start(_scheduler);
return task;
}
这里,假设
_schduler
持有 ui TaskScheduler
。但我不太习惯创建“冷”任务并使用 start 方法来运行它们。这是“推荐”的方式还是有更优雅的方式来做到这一点?
InvokeAsync
代替 Invoke
,然后在函数返回的 Task<int>
中返回
DispatcherOperation<int>
。
//Coding conventions say async functions should end with the word Async.
public Task<int> RunOnUiAsync(Func<int> f)
{
var dispatcherOperation = Application.Current.Dispatcher.InvokeAsync(f);
return dispatcherOperation.Task;
}
如果您无法访问.NET 4.5,情况会稍微复杂一些。您将需要使用
BeginInvoke
和 TaskCompletionSource
来包装 DispaterOperation
返回的
BeginInvoke
public Task<int> RunOnUi(Func<int> f)
{
var operation = Application.Current.Dispatcher.BeginInvoke(f);
var tcs = new TaskCompletionSource<int>();
operation.Completed += (sender, args) => tcs.TrySetResult((int)operation.Result);
operation.Aborted += (sender, args) => tcs.TrySetException(new SomeExecptionHere());
//The operation may have already finished and this check accounts for
//the race condition where neither of the events will ever be called
//because the events where raised before you subscribed.
var status = operation.Status;
if (status == DispatcherOperationStatus.Completed)
{
tcs.TrySetResult((int)operation.Result);
}
else if (status == DispatcherOperationStatus.Aborted)
{
tcs.TrySetException(new SomeExecptionHere());
}
return tcs.Task;
}