c# - 等待 RunOnUIThread 完成并继续执行剩余的任务

Question

我正在通过 c#(xamarin.visual studio) 为 android 开发一个应用程序，问题是我有一些任务要在其他线程中运行，当它应该更新布局时它应该调用 Activity.RunOnUIThread ，一切正常，但线程不等待此方法完成并继续执行其余部分而无需等待。

问题是:如何等待 RunOnUIThread 完成，然后继续执行任务的其余命令。 ？

public void start(int threadCounter)
    {
        for (int i = 0; i < threadCounter; i++)
        {

            Thread thread1 = new Thread(new ThreadStart(RunScanTcp));
            thread1.Start();

        }

    }
    public void RunScanTcp()
    {

        int port;

        //while there are more ports to scan 
        while ((port = portList.NextPort()) != -1)
        {
            count = port;

            Thread.Sleep(1000); //lets be a good citizen to the cpu

            Console.WriteLine("Current Port Count : " + count.ToString());

            try
            {

                Connect(host, port, tcpTimeout);

            }
            catch
            {
                continue;
            }

            Activity.RunOnUiThread(() =>
            {
                mdata.Add(new data() { titulli = "Port : " + port, sekuenca = "Sequence : ", ttl = "Connection Sucessfull !", madhesia = "", koha = "Time : " });
                mAdapter.NotifyItemInserted(mdata.Count() - 1);
                if (ndaluar == false)
                {
                    mRecyclerView.ScrollToPosition(mdata.Count() - 1);
                }
            }); // in that point i want to wait this to finish and than continue below...
            Console.WriteLine("TCP Port {0} is open ", port);

        }

Answer 1

首先你应该避免创建新的Threads。在您的情况下，您必须使用 ThreadPool.QueueUserWorkItem 来排队 CPU 绑定(bind)操作。然后，您可以使用 ManualResetEventSlim 或 TaskCompletionSource 来同步 UI 线程 和工作线程。

例子:

// mre is used to block and release threads manually. It is
// created in the unsignaled state.

ManualResetEventSlim mre = new ManualResetEventSlim(false);

RunOnUiThread(() =>
{            
    // Update UI here.
    // Release Manual reset event.

    mre.Set();
});

// Wait until UI operations end.
mre.Wait();

---

在您的具体情况下:

for (int i = 0; i < threadCounter; i++)
{
    ThreadPool.QueueUserWorkItem(RunScanTcp);
}

private void RunScanTcp(object stateInfo) 
{
    // Do CPU bound operation here.
    var a = 100;
    while (--a != 0)
    {
        // mre is used to block and release threads manually. It is
        // created in the unsignaled state.
        ManualResetEventSlim mre = new ManualResetEventSlim(false);

        Activity.RunOnUiThread(() =>
        {
            // Update UI here.

            // Release Manual reset event.
            mre.Set();
        });

        // Wait until UI operation ends.
        mre.WaitOne();
    }
}

如果您更喜欢使用 TaskCompletionSource，您可以使用替代方法:

private async void RunScanTcp(object stateInfo)
{
    // Do CPU bound operation here.
    var a = 100;
    while (--a != 0)
    {
        // using TaskCompletionSource
        var tcs = new TaskCompletionSource<bool>();

        RunOnUiThread(() =>
        {
            // Update UI here.

            // Set result
            tcs.TrySetResult(true);
        });

        // Wait until UI operationds.
        tcs.Task.Wait();
    }
}