android - 线程上的 robolectric runOnUiThread 不起作用

Question

runOnUiThread() 在线程内执行时似乎不起作用。有人知道解决方法吗？

注意:我在这里提交了工单 - https://github.com/robolectric/robolectric/issues/2479

import android.app.Activity;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.robolectric.Robolectric;
import org.robolectric.RobolectricGradleTestRunner;
import org.robolectric.annotation.Config;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;

import static org.junit.Assert.assertTrue;

@RunWith(RobolectricGradleTestRunner.class)
@Config(constants = BuildConfig.class, sdk = 21)
public class RunOnUiThreadTest {

    /**
     * Works
     * @throws Exception
     */
    @Test
    public void inside_the_main_thread() throws Exception {
        final Activity activity = Robolectric.setupActivity(Activity.class);
        final CountDownLatch latch = new CountDownLatch(1);
        final AtomicBoolean didRun = new AtomicBoolean(false);

        activity.runOnUiThread(new Runnable() {
            @Override
            public void run() {
                didRun.set(true);
                latch.countDown();
            }
        });

        latch.await(20, TimeUnit.SECONDS);
        assertTrue(didRun.get());
    }

    /**
     * Fails
     * @throws Exception
     */
    @Test
    public void inside_a_new_thread() throws Exception {
        final Activity activity = Robolectric.setupActivity(Activity.class);
        final CountDownLatch latch = new CountDownLatch(1);
        final AtomicBoolean didRun = new AtomicBoolean(false);

        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                activity.runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        didRun.set(true);
                        latch.countDown();
                    }
                });
            }
        });
        thread.start();

        latch.await(20, TimeUnit.SECONDS);
        assertTrue(didRun.get());
    }

}

Answer 1

由于第二个测试阻止了运行目标 Runnable 所需的 UI 线程，因此测试的结果很可能符合预期。

第一个测试会通过，因为整个方法是同步执行的。由于您已经在 UI 线程上，因此当调用 activity.runOnUiThread(...) 时，Runnable 将立即执行。由于 latch 为 0 latch.await(20, TimeUnit.SECONDS) 立即返回并且断言为真。

在第二个示例中，您启动了一个新线程并从其中调用 activity.runOnUiThread(...)。由于您不在 UI 线程上，因此 Runnable 被发布到 UI 线程上的 Handler 以在将来异步执行。此时，您继续从 UI 线程调用 latch.await(20, TimeUnit.SECONDS);，这意味着 Runnable 无法在此期间运行，因为您阻止了界面线程。

20 秒后线程恢复，但 Runnable 从未有机会运行，因此断言失败，因为 didRun() 从未设置为 true。

下面是一个更新的测试，它允许使用 runOnUiThread() 发布的 Runnable 运行。

@Test
public void inside_a_new_thread() throws Exception {
    final Activity activity = Robolectric.setupActivity(Activity.class);
    final CountDownLatch latch = new CountDownLatch(1);
    final AtomicBoolean didRun = new AtomicBoolean(false);

    Thread thread = new Thread(new Runnable() {
        @Override
        public void run() {
            activity.runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    didRun.set(true);
                    latch.countDown();
                }
            });
        }
    });
    thread.start();

    // sleep current thread to give the new thread a chance to run and post the runnable
    Thread.sleep(1000);

    // This method will cause the runnable to be executed
    Robolectric.flushForegroundThreadScheduler();

    // Should immediately return since the runnable has been executed
    latch.await(20, TimeUnit.SECONDS);
    assertTrue(didRun.get());
}