使用 android 处理程序时，如何解决有关 memory 泄漏的警告？

Question

我是学习android的初学者。 我在学习 Thread 时使用了 Handler。 顺便说一句，我在 android studio 中使用 Handler 警告 memory 泄漏。 我搜索了很多不同的问题，但没有与我的案例相对应的部分。 使用处理程序时，如何解决有关 memory 泄漏的警告？

public class HandlerActivity extends AppCompatActivity implements Runnable {

    ProgressBar pb;
    TextView txtRate;
    Button btnStart;
    static int value;

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

        pb = findViewById(R.id.pb);
        txtRate = findViewById(R.id.txtRate);
        btnStart = findViewById(R.id.btnStart);

        btnStart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Thread th = new Thread(HandlerActivity.this);
                th.start();
            }
        });
    }

        Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            pb.setProgress(value);
            txtRate.setText("Process : " + value + "%");
        }
    };

    @Override
    public void run() {
        for (int i = 1; i <= 100; i++) {
            value = i;

            handler.sendEmptyMessage(0);

            try {
                Thread.sleep(100);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                Toast.makeText(HandlerActivity.this, "Progress Done !", Toast.LENGTH_SHORT).show();
            }
        });
    }
}

Answer 1

基本上TextView或任何其他View持有代表相应Activity的Context object 的引用。 当您在Thread中保留对任何View的强引用时，您不仅存储了View object，而且还存储了一个Context object 代表创建它的Activity 。 现在由于Thread不与 Activity 生命周期绑定，即使在Activity被销毁后它们也会继续运行。 如果是这种情况， Thread将通过该View object 保存已破坏的Activity引用，从而创建 memory 泄漏。

上述问题可以通过存储View object 的弱引用来解决，以便 GC 可以在必要时对其进行垃圾回收。 通过以下方式，您可以摆脱 memory 泄漏：

public class HandlerActivity extends AppCompatActivity implements Runnable {
    WeakReference<ProgressBar> pb;
    WeakReference<TextView> txtRate;
    Button btnStart;
    static int value;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        ...
        pb = new WeakReference<>(findViewById(R.id.pb)); // you may require to cast findViewById() to ProgressBar
        txtRate = new WeakReference<>(findViewById(R.id.txtRate));  // you may require to cast findViewById() to TextView
        ...
    }

    Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            if(pb.get()!=null) pb.get().setProgress(value);
            if(txtRate.get()!=null) txtRate.get().setText("Process : " + value + "%");
        }
    };

    @Override
    public void run() {
        for (int i = 1; i <= 100; i++) {
            // Its always recommended to check if activity is running and stop the thread if not running
            if(isFinishing() || isDestroyed()) {
                return;
            }
        }
    }
}

Answer 2

Roaim, Mark Keen 在他们的帮助下，我解决了这个问题并自己给出了完整的答案。 感谢 Roaim，Mark Keen。

public class HandlerActivity extends AppCompatActivity implements Runnable {

ProgressBar pb;
TextView txtRate;
Button btnStart;
int value;

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

    pb = findViewById(R.id.pb);
    txtRate = findViewById(R.id.txtRate);
    btnStart = findViewById(R.id.btnStart);

    btnStart.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Thread th = new Thread(HandlerActivity.this);
            th.start();
        }
    });
}

private static class WeakHandler extends Handler {
    private final WeakReference<HandlerActivity> mWeakActivity;

    private WeakHandler(HandlerActivity AppCompatActivity) {
        mWeakActivity = new WeakReference<>(AppCompatActivity);
    }

    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        HandlerActivity _activity = mWeakActivity.get();

        if (_activity != null) {

            switch (msg.what) {
                case 0:
                    _activity.pb.setProgress(_activity.value);
                    _activity.txtRate.setText("Process : " + _activity.value + "%");
                    break;
            }
        }
    }
}

private final WeakHandler mHandler = new WeakHandler(this);

@Override
public void run() {
    for (int i = 1; i <= 100; i++) {
        value = i;

        mHandler.sendEmptyMessage(0);

        try {
            Thread.sleep(100);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    runOnUiThread(new Runnable() {
        @Override
        public void run() {
            Toast.makeText(HandlerActivity.this, "Progress Done !.", Toast.LENGTH_SHORT).show();
        }
    });
}

}