异步方法冻结UI [英] async method freezes UI

问题描述

预期结果:

TestAsync，工作线程执行LongTask.

实际结果:

Ui线程执行所有操作

Ui thread executes everything

测试:

public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
    // [...]

    _fab = root.FindViewById<FloatingActionButton>(...);
    _fab.Click += ((sender, v) =>  TestAsync("fab"));

    // [...]
}

private async void TestAsync(string origin)
{
    await LongTask(); 
}

private async Task LongTask()
{
    while (true) { } // Thread should hung here
}

结果:UI冻结.

测试2 : 为了确保UI能够执行所有操作，我改为进行了网络操作(Android的UI线程中不允许这样做)

Test 2: In order to make sure the UI is executing everything, I made a network operation instead (which is not allowed in the UI thread in Android)

public async Task<int> Network(string s)
{
    URL url = new URL("http://www.randomtext.me/api/");
    Java.IO.BufferedReader reader = new Java.IO.BufferedReader(new Java.IO.InputStreamReader(url.OpenStream()));

    int count = 0;
    string str;
    while ((str = reader.ReadLine()) != null) {
        count += str.Length;
    }
    reader.Close();

    await Task.Delay(3000); // To make sure this method is compiled as async even though it isn't necessary

    return count;
}

结果:NetworkOnMainThreadException.

问题:

为什么在工作线程中不执行LongTask或Network方法?那么await/async是什么?

Why aren't LongTask nor Network methods executed in a worker thread ? What are await/async for then ?

谢谢.

推荐答案

然后一个工作线程执行LongTask.

and a worker thread executes LongTask.

不，那不会自己发生.您正在等待GUI线程，因此将其阻止.对于异步I/O，此模式是可以的，因为这将释放线程.

No, that won't happen by itself. You await from the GUI thread and so you will block it. This pattern is OK for async I/O because that will free up the Thread.

但是当您的情况受CPU限制时，异步/等待没有用，请使用Task.Run:

But when your case is CPU bound, there is no use for async/await, use Task.Run:

private void TestAsync(string origin)
{
    Task.Run( LongTask); 
}

这篇关于异步方法冻结UI的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！