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Android 内存泄漏的一些情况。
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); } };}
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); } };}
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。