使用 ExecutorService 的 awaitTermination 方法时如何显示进度条？

Question

我正在构建一个应用程序，它从多个网页中抓取价格，然后在所有任务完成后显示结果。一切正常，除了我正在努力添加进度条。

以下是我正在尝试做的简化版本。按下按钮后，程序运行 2 个任务：第一个任务休眠 3 秒，第二个任务 - 7 秒。全部完成后，将显示来自每个任务的 toast 消息。

公共类 MainActivity 扩展 AppCompatActivity {

Button button;
ProgressBar progressBar;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    button = findViewById(R.id.btn);
    progressBar = findViewById(R.id.pb);

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            progressBar.setVisibility(View.VISIBLE);

            ExecutorService executorService = Executors.newFixedThreadPool(5);

            executorService.submit(new Task1());
            executorService.submit(new Task2());

            executorService.shutdown();

            try {
                executorService.awaitTermination(1, TimeUnit.MINUTES);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

            progressBar.setVisibility(View.INVISIBLE);

        }
    });



}

private class Task1 implements Runnable {
    @Override
    public void run() {
        try {
            Thread.sleep(3000);
            Log.d("task1", "run: ");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                Toast.makeText(MainActivity.this, "task1", Toast.LENGTH_SHORT).show();
            }
        });
    }
}

private class Task2 implements Runnable {

    @Override
    public void run() {
        try {
            Log.d("task2", "run: ");
            Thread.sleep(7000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                Toast.makeText(MainActivity.this, "task2", Toast.LENGTH_SHORT).show();
            }
        });
    }
}

}

据我了解，问题是使用 awaitTermination 方法时所有线程都被阻塞，包括 UI 线程，因此只有在所有任务完成后才会显示任务结果。

有没有办法等到所有任务完成，同时仍然显示进度条？

Answer 1

是的，您对awaitTermination 的看法是正确的。但是它只阻塞了主线程，其他的都没有。

解决问题的一种方法是定义活动任务计数器。每次运行任务时，它都会增加。每次任务结束（包括失败）计数器都会减少。

当然你应该删除awaitTermination 方法。在 Android 中（主要是在所有与 UI 相关的框架中），您不应阻塞 UI 线程。

我的命题的伪代码：

Button button;
ProgressBar progressBar;
int activeTaskCounter = 0;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    button = findViewById(R.id.btn);
    progressBar = findViewById(R.id.pb);

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            ExecutorService executorService = Executors.newFixedThreadPool(5);

            executorService.submit(new Task1());
            executorService.submit(new Task2());
            executorService.shutdown();
        }
    });
}

private void increaseActiveCounter() {
    activeTaskCounter += 1;
    progressBar.setVisibility(View.VISIBLE);
}

private void decreaseActiveCounter() {
    activeTaskCounter -= 1;
    if (activeTaskCounter == 0) {
        progressBar.setVisibility(View.INVISIBLE);
    }
}

private class Task1 implements Runnable {
    @Override
    public void run() {
        // It's lambda here, but you can use anonymous class. It's up to you
        runOnUiThread(() -> increaseCounter());
        try {
            Thread.sleep(3000);
            Log.d("task1", "run: ");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            runOnUiThread(() -> decreaseActiveCounter());
        }
       
    }
}

private class Task2 implements Runnable {

    @Override
    public void run() {
        runOnUiThread(() -> increaseCounter());
        try {
            Thread.sleep(7000);
            Log.d("task2", "run: ");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            runOnUiThread(() -> decreaseActiveCounter());
        }
    }
}