发现问题 (FragmentPageAdapter)

因为FragmentPageAdapter在超出缓存的页面后,只是将fragment中的mView设置为空,但是fragment对象的引用还在,由于我使用了ButterKnife,在fragment的对象中有个imageView的成员变量,导致imageView无法回收.而如果使用了FragmentStatePagerAdapter,则会将fragment的直接置空,不会出现内存释放不了的问题

FragmentPageAdapter 与FragmentStatePageAdapter的区别

FragmentPageAdapter的源码

@Override
  public Object instantiateItem(ViewGroup container, int position) {
      if (mCurTransaction == null) {
          mCurTransaction = mFragmentManager.beginTransaction();
      }

      final long itemId = getItemId(position);

      // Do we already have this fragment?
      String name = makeFragmentName(container.getId(), itemId);
      Fragment fragment = mFragmentManager.findFragmentByTag(name);
      if (fragment != null) {
          if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
          mCurTransaction.attach(fragment);//因为fragment实例没有被真正释放，所以可以直接attach效率高
      } else {
          fragment = getItem(position);//初始化页面的时候拿到fragment的实例
          if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
          mCurTransaction.add(container.getId(), fragment,
                  makeFragmentName(container.getId(), itemId));//add上去
      }
      if (fragment != mCurrentPrimaryItem) {
          fragment.setMenuVisibility(false);
          fragment.setUserVisibleHint(false);
      }

      return fragment;
  }

  @Override
  public void destroyItem(ViewGroup container, int position, Object object) {
      if (mCurTransaction == null) {
          mCurTransaction = mFragmentManager.beginTransaction();
      }
      if (DEBUG) Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object
              + " v=" + ((Fragment)object).getView());
      mCurTransaction.detach((Fragment)object);//并没有真正释放fragment对象只是detach
  }

FragmentStatePageAdapter的destroy

@Override
  public Object instantiateItem(ViewGroup container, int position) {
      // If we already have this item instantiated, there is nothing
      // to do.  This can happen when we are restoring the entire pager
      // from its saved state, where the fragment manager has already
      // taken care of restoring the fragments we previously had instantiated.
      if (mFragments.size() > position) {
          Fragment f = mFragments.get(position);//fragment被释放后这里得到的null值
          if (f != null) {
              return f;
          }
      }

      if (mCurTransaction == null) {
          mCurTransaction = mFragmentManager.beginTransaction();
      }

      Fragment fragment = getItem(position);//fragment被释放后或者是初次进入页面拿到新的Fragment实例
      if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
      if (mSavedState.size() > position) {
          Fragment.SavedState fss = mSavedState.get(position);
          if (fss != null) {
              fragment.setInitialSavedState(fss);
          }
      }
      while (mFragments.size() <= position) {
          mFragments.add(null);
      }
      fragment.setMenuVisibility(false);
      fragment.setUserVisibleHint(false);
      mFragments.set(position, fragment);
      mCurTransaction.add(container.getId(), fragment);//新的Fragment实例 是add上去的

      return fragment;
  }

 @Override
  public void destroyItem(ViewGroup container, int position, Object object) {
      Fragment fragment = (Fragment) object;

      if (mCurTransaction == null) {
          mCurTransaction = mFragmentManager.beginTransaction();
      }
      if (DEBUG) Log.v(TAG, "Removing item #" + position + ": f=" + object
              + " v=" + ((Fragment)object).getView());
      while (mSavedState.size() <= position) {
          mSavedState.add(null);
      }
      mSavedState.set(position, fragment.isAdded()
              ? mFragmentManager.saveFragmentInstanceState(fragment) : null);
      mFragments.set(position, null);//真正释放了fragment实例

      mCurTransaction.remove(fragment);
  }

引用ViewPager 全面剖析及使用详解 - 简书

FragmentPageAdapter解决方案

在Fragment-->onDestroyView()的时候,将含有bitmap的imageView移除.

((ViewGroup) imageView.getParent()).removeView(imageView);

引用自 android - FragmentStatePagerAdapter OutOfMemoryError - Stack Overflow

protected void onDestroy(){
  super.onDestroy();   
  unbindDrawables(getView()); // <---This should be the ID of this fragments (ScreenSlidePageFragment) layout
}
private void unbindDrawables(View view){ 
  if (view.getBackground() != null)   { 
     view.getBackground().setCallback(null);  
   }   
  if (view instanceof ViewGroup && !(view instanceof AdapterView))   { 
       for (int i = 0; i < ((ViewGroup) view).getChildCount(); i++)      {
           unbindDrawables(((ViewGroup) view).getChildAt(i));      
      }
      ((ViewGroup) view).removeAllViews(); 
  }
}