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Android 内存泄漏的一些情况。

时间:2016-09-01 15:54:24      阅读:318      评论:0      收藏:0      [点我收藏+]

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最近在维护代码,发现一个自定义View(这个View是在一个AsyncTask的工作线程doInBackground中新建的,在UI线程onPostExecute中添加进window中的)经常会泄漏内存,导致其引用的Activity一直得不到释放,每次退出再进去都会导致Activity的对象+1.

package com.xxx.launcher.view;

import android.content.Context;
import android.util.Log;
import android.view.View;

public class WeatherTextView extends SkinTextView {

    public WeatherTextView (Context context) {
super(context); postDelayed(mShowCityRunnable,
200);//这一步有问题 } @Override protected void onWindowVisibilityChanged(int visibility) { super.onWindowVisibilityChanged(visibility); if (visibility == View.VISIBLE) { post(mShowCityRunnable); } } @Override protected void onDetachedFromWindow() { super.onDetachedFromWindow(); onCancel(); }; public void onCancel(){ removeCallbacks(mShowCityRunnable); } private Runnable mShowCityRunnable = new Runnable() { @Override public void run() { Log.i("mShowCityRunnable-------TAG", "run"+mShowCityRunnable); setText(city); } }; }

 

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最后通过MAT工具查看内存快照的比较,发现了如下的情况,把内存泄露的地方锁定在了WeatherTextView$2的第二个内部类中mShowCityRunnable ,一开始始终都想不到这个内部类到底有什么地方泄露了,最后突然灵光一闪,是不是View的post()方法导致的,在网上一查,发现确实。

public boolean post(Runnable action) {  
    Handler handler;  
    AttachInfo attachInfo = mAttachInfo;  
    if (attachInfo != null) {  
        handler = attachInfo.mHandler;  
    } else {  
        // Assume that post will succeed later  
        ViewRootImpl.getRunQueue().post(action);  
        return true;  
    }  
  
    return handler.post(action);  
}  

在post() 函数注释中,明确写着:This method can be invoked from outside of the UI thread only when this View is attached to a window.

当View还没有attach到当前window时,mAttachInfo 值为 null,故而执行 else语句,再看一下getRunQueue()和其post() 方法:

static final ThreadLocal<RunQueue> sRunQueues = new ThreadLocal<RunQueue>();  
  
static RunQueue getRunQueue() {  
     RunQueue rq = sRunQueues.get();  
     if (rq != null) {  
         return rq;  
     }  
     rq = new RunQueue();  
     sRunQueues.set(rq);  
     return rq;  
 }  
 ……  
 static final class RunQueue {  
     private final ArrayList<HandlerAction> mActions = new ArrayList<HandlerAction>();  
  
     void post(Runnable action) {  
         postDelayed(action, 0);  
     }  
  
     void postDelayed(Runnable action, long delayMillis) {  
         HandlerAction handlerAction = new HandlerAction();  
         handlerAction.action = action;  
         handlerAction.delay = delayMillis;  
  
         synchronized (mActions) {  
             mActions.add(handlerAction);  
         }  
     }  
        
     void executeActions(Handler handler) {  
         synchronized (mActions) {  
             final ArrayList<handleraction> actions = mActions;  
             final int count = actions.size();  
  
             for (int i = 0; i < count; i++) {  
                 final HandlerAction handlerAction = actions.get(i);  
                 handler.postDelayed(handlerAction.action, handlerAction.delay);  
             }  
  
             actions.clear();  
         }  
     }  
     ……  
 }  

这样会把Runnable 插入到一个静态的ThreadLocal的RunQueue队列里(在工作线程中post,就会插入工作线程的RunQueue队列),针对本文开头给出的例子,那么插入的Runnable什么时候得到执行呢?

调用RunQueue.executeActions()方法只有一处,即在ViewRootImpl类的如下非静态方法中

private void performTraversals() {  
      
        if (mLayoutRequested && !mStopped) {  
            // Execute enqueued actions on every layout in case a view that was detached  
            // enqueued an action after being detached  
            getRunQueue().executeActions(attachInfo.mHandler);  
        }  
}  

该方法是在UI线程执行的(见ViewRootImpl.handleMessage()), 故当UI线程执行到该performTraversals() 里的 getRunQueue() 时,得到的是UI线程中的RunQueue,这样AsyncTask 线程中的 RunQueue永远不会被执行到, 并且AsyncTask的是用线程池实现的,AsyncTask启动的线程会长期存在,造成如下引用关系:

 

AsyncTask线程 => 静态的ThreadLocal的RunQueue => Runnable => View=> Activity;

如此即使activity finish 了,确始终存在一个静态引用链引用这该activity,而 Activity一般又引用着很多资源,比如图片等,最终造成严重资源泄漏。

最后我是写改成

package com.xxx.launcher.view;

import android.content.Context;
import android.util.Log;
import android.view.View;

public class WeatherTextView  extends SkinTextView {

    public WeatherTextView (Context context) {
        super(context);
    }
    
    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        postDelayed(mShowCityRunnable, 200); //在onAttachedToWindow方法中执行post方法
    }
    
    @Override
    protected void onWindowVisibilityChanged(int visibility) {
        super.onWindowVisibilityChanged(visibility);    
        if (visibility == View.VISIBLE) {
            post(mShowCityRunnable);
        }
    }
    
    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        onCancel();
    };
    
    public void onCancel(){
        removeCallbacks(mShowCityRunnable);
    }
    private Runnable mShowCityRunnable = new Runnable() {

        @Override
        public void run() {
            Log.i("mShowCityRunnable-------TAG", "run"+mShowCityRunnable);
            setText(city);
        }
    };
}

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这样Activity就没有再被其他东西引用了,就不会发生Activity的泄漏了,Activity就可以被释放了。这样,不管进入退出进入这个MainMenuActivity多少次,MainMenuActivity的对象就只会保存一份。

ps:至于为什么在两个Histogram(直方图)的比较图中还是显示MainMenuActivity+1,则是因为这是类名,类被加载之后,在进程结束之前不会被回收

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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这种泄漏一般是因为mStorageManager 注册了但是没有取消注册

mStorageManager = (StorageManager) mContext.getSystemService(Context.STORAGE_SERVICE);
mStorageManager.registerListener(mStoragelistener);

取消注册就可以了

if (mStorageManager != null) {
    mStorageManager.unregisterListener(mStoragelistener);
}

 

 

Android 内存泄漏的一些情况。

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原文地址:http://www.cnblogs.com/lipeineng/p/5829848.html

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