从Thread返回值 [英] Returning value from Thread

问题描述

我有一个带 HandlerThread 的方法。值在 Thread 中更改，我想将其返回到 test（）方法。有没有办法做到这一点？

I have a method with a HandlerThread. A value gets changed inside the Thread and I'd like to return it to the test() method. Is there a way to do this?

public void test()
{   
    Thread uiThread = new HandlerThread("UIHandler"){
        public synchronized void run(){
            int value; 
            value = 2; //To be returned to test()
        }
    };
    uiThread.start();
}

推荐答案

您可以使用本地决赛变量数组。变量需要是非基本类型，因此您可以使用数组。您还需要同步两个线程，例如使用 CountDownLatch ：

You can use a local final variable array. The variable needs to be of non-primitive type, so you can use an array. You also need to synchronize the two threads, for example using a CountDownLatch:

public void test()
{   
    final CountDownLatch latch = new CountDownLatch(1);
    final int[] value = new int[1];
    Thread uiThread = new HandlerThread("UIHandler"){
        @Override
        public void run(){
            value[0] = 2;
            latch.countDown(); // Release await() in the test thread.
        }
    };
    uiThread.start();
    latch.await(); // Wait for countDown() in the UI thread. Or could uiThread.join();
    // value[0] holds 2 at this point.
}

您还可以使用 执行者 和 Callable 像这样：

You can also use an Executor and a Callable like this:

public void test() throws InterruptedException, ExecutionException
{   
    ExecutorService executor = Executors.newSingleThreadExecutor();
    Callable<Integer> callable = new Callable<Integer>() {
        @Override
        public Integer call() {
            return 2;
        }
    };
    Future<Integer> future = executor.submit(callable);
    // future.get() returns 2 or raises an exception if the thread dies, so safer
    executor.shutdown();
}

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