使用 android 處理程序時，如何解決有關 memory 泄漏的警告？

Question

我是學習android的初學者。 我在學習 Thread 時使用了 Handler。 順便說一句，我在 android studio 中使用 Handler 警告 memory 泄漏。 我搜索了很多不同的問題，但沒有與我的案例相對應的部分。 使用處理程序時，如何解決有關 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持有代表相應Activity的Context object 的引用。 當您在Thread中保留對任何View的強引用時，您不僅存儲了View object，而且還存儲了一個Context object 代表創建它的Activity 。 現在由於Thread不與 Activity 生命周期綁定，即使在Activity被銷毀后它們也會繼續運行。 如果是這種情況， Thread將通過該View object 保存已破壞的Activity引用，從而創建 memory 泄漏。

上述問題可以通過存儲View object 的弱引用來解決，以便 GC 可以在必要時對其進行垃圾回收。 通過以下方式，您可以擺脫 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 在他們的幫助下，我解決了這個問題並自己給出了完整的答案。 感謝 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();
        }
    });
}

}