从线程返回值

android multithreading java

2022-08-31 09:12:35

我有一个带有.一个值在里面被更改，我想把它返回到方法。有没有办法做到这一点？HandlerThreadThreadtest()

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

答案 1

通常你会像这样做

 public class Foo implements Runnable {
     private volatile int value;

     @Override
     public void run() {
        value = 2;
     }

     public int getValue() {
         return value;
     }
 }

然后，您可以创建线程并检索值（假设已设置该值）

Foo foo = new Foo();
Thread thread = new Thread(foo);
thread.start();
thread.join();
int value = foo.getValue();

tl;dr线程不能返回值（至少没有回调机制就不能）。您应该像引用普通类一样的线程并请求值。

答案 2

可以使用局部最终变量数组。变量必须是非基元类型，因此可以使用数组。您还需要同步两个线程，例如使用 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.
}

您还可以使用执行器和可调用程序，如下所示：

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();
}