如何解决使用 android 处理程序时有关内存泄漏的警告?

Question

我是一个学习安卓的初学者。 我在学习线程时使用处理程序。 顺便说一下，我使用Handler来警告android工作室中的内存泄漏。 我搜索了很多不同的问题，但我没有与我的情况相对应的部分。 如何解决使用处理程序时有关内存泄漏的警告？

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都持有表示相应Activity的Context对象的引用。在Thread中保留对任何View的强引用时，您不仅存储了View对象，而且还存储了一个表示创建它的Activity的Context对象。现在，由于Thread与活动生命周期无关，因此即使在Activity被销毁后，它们仍将继续运行。如果是这种情况，Thread将通过该View对象保存已销毁Activity的引用，从而产生内存泄漏。

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

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();
}
});
}

}