wpf 在 UI 线程上创建和启动任务
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原文地址: http://stackoverflow.com/questions/28194943/
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Creating and starting a task on the UI thread
提问by Kobi Hari
When a method that gets called on a worker thread needs to run code on the UI thread and wait for it to complete before doing something else, it can be done like this:
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它完成后再做其他事情时，可以这样做：
public int RunOnUi(Func<int> f)
{
int res = Application.Current.Dispatcher.Invoke(f);
return res;
}
But what if I wanted to do it with tasks? Is there a way for the RunOnUi method to create a task that is started on the UI and return it so that the caller (which runs on a worker thread) can wait for it? Something that will fit the following signature: public Task<int> StartOnUi(Func<int> f)?
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？符合以下签名的内容：public Task<int> StartOnUi(Func<int> f)?
One way to do it is as follows:
一种方法如下：
public Task<int> RunOnUi(Func<int> f)
{
var task = new Task<int>(f);
task.Start(_scheduler);
return task;
}
Here, assume that _schdulerholds the ui TaskScheduler. But I am not too comfortable with creating "cold" tasks and using the start method to run them. Is that the "recommended" way or is there a more elegant way to do it?
在这里，假设_schduler持有 ui TaskScheduler。但是我不太习惯创建“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？
采纳答案by Scott Chamberlain
Just use InvokeAsyncinstead of Invokethen return the Task<int>inside the DispatcherOperation<int>the function returns.
只需使用InvokeAsync而不是Invoke然后返回函数返回的Task<int>内部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;
}
If you do not have access to .NET 4.5 it is a little more complicated. You will need to use BeginInvokeand a TaskCompletionSourceto wrap the DispaterOperationthat BeginInvokereturns
如果您无法访问 .NET 4.5，则情况会稍微复杂一些。您将需要使用BeginInvoke和TaskCompletionSource包装的DispaterOperation那BeginInvoke回报
public Task<int> RunOnUi(Func<int> f)
{
var operation = Application.Current.Dispatcher.BeginInvoke(f);
var tcs = new TaskCompletionSource<int>();
operation.Aborted += (sender, args) => tcs.TrySetException(new SomeExecptionHere());
operation.Completed += (sender, args) => tcs.TrySetResult((int)operation.Result);
//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;
}
