Android项目：模仿ConvertView原理(ListView的getView方法)对View对象进行回收和复用
在项目优化过程中,通过MAT监控发现存在一处内存泄露,反复进入某个页面,内存占用越来越大。后分析找到了泄露原因,原来是在自定义列表中,将行布局的layout文件inflate成view对象的时候,每加载一次列表就要new出一组新的view对象。因为没有对这些布局一致的view进行复用,又没法及时释放,导致了列表的行布局对象越积越多,造成内存泄露。 解决这个oom问题,首先想到了listview加载中对convertview的回收和复用的方法。于是模仿convertview的原理写了个对view对象进行回收和复用的类,此处类名为ViewRecycler,使用后有效的解决了view对象的复用,远离这个棘手的oom问题。由于项目中需要复用的view对象布局都是一样的,此方法只考虑了复用同一布局的情况。同时,项目中的列表已有获取显示行与隐藏行的相应接口,此方法仅主要从回收与复用的逻辑层面加以实现,并未涉及任何底层代码部分。 一、以下是具体的实现过程: 1.首先ViewRecycler类需要两个容器分别用来保存活动的View对象和回收可复用的View对象。一个map用来保存回收的View(无序添加),一个数组用来记录当前显示的行号以及对应的View(有序添加)。 如下: 1 2 private SparseArray<View> recycleViews; // 废弃的view private View[] activeViews = new View[ 0 ]; //正在使用的view 注:key为int类型的HashMap用SparseArray代替,会有更好的性能. 2.每次列表刷新或变化,就更新一次activeViews的大小。即activeViews的数组长度与当前列表的总行数一致。在刷新列表或者加载更多时,调用getCount()方法更新activeViews数组长度。 如下: 1 2 3 4 5 6 // 加载完毕 private void loadComplete() { //..... mViewRecycler.getCount(mDataList.size()); } ViewRecycler类里的getCount方法: 1 2 3 4 5 6 7 8 9 10 11 12 /** 获取活动view的总数 */ public void getCount( int count) { final int length = this .activeViews.length; if (count > length) { final View[] activeViews = this .activeViews; this .activeViews = Arrays.copyOf(activeViews, count); // Log.e("getCount", "activeViews[" + (count - 1) + "]=" + this.activeViews[count-1]); } } 3.列表每新增显示一行,就先获取是否有可复用的View对象。先判断recycleViews是否已存有该行号对应的View,没有则获取最新回收的View。再结合setTag与getTag便可实现对回收View对象的复用了。如果recycleViews没有可复用的View,则inflate生成新的View。 如下: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 public void convertFromView( final ListJson listJson, final int n) { ViewHolder holder = null ; // 判断是否有可重复利用的view View resycleView = mViewRecycler.getRecycleView(n); if (resycleView == null ) { resycleView = LayoutInflater.from(getActivity()).inflate(R.layout.list_item, null ); holder = new ViewHolder(); //..... holder.iv_main = (ImageView) resycleView.findViewById(R.id.item_iv_main); resycleView.setTag(holder); } else { holder = (ViewHolder) resycleView.getTag(); } //保存新增活动的View对象 mViewRecycler.addActiveView(n, resycleView); // 加载行布局数据 holder.tv_title.setText(lison.getName()); holder.tv_price.setText( "待定" ); //..... // 下载图片 ImageLoadingListener listener = new ImageLoadingListener() { @Override public void onLoadingStarted(String arg0, View arg1) { } @Override public void onLoadingComplete(String arg0, View arg1, Bitmap bitmap) { //获取view对象 View bitmapView = mViewRecycler.getActiveView(n); if (bitmapView != null ) { ViewHolder holder = (ViewHolder) bitmapView.getTag(); if (holder != null ) { // 加载图片 holder.iv_main.setImageBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.bg_item)); } } } @Override public void onLoadingFailed(String arg0, View arg1, FailReason arg2) { } @Override public void onLoadingCancelled(String arg0, View arg1) { } }; imageLoader.loadImage(listJson.getStatusPic(), listener); } ViewRecycler类里的对应方法: (1)将行号与对应的View填充到activeViews数组里保存。添加前对行号与activeViews的长度进行校正,避免越界。 1 2 3 4 5 6 7 8 9 10 11 12 /** 添加记录当前活动的view */ public void addActiveView( int position, View view) { final int length = this .activeViews.length; if (position > length - 1 ) { getCount(position + 1 ); } this .activeViews[position] = view; // Log.e("addActiveView", "activeViews.size() = " + Arrays.toString(activeViews)); } (2)根据行号获取对应的View对象。 1 2 3 4 5 6 7 8 9 10 /** 获取某个活动view */ public View getActiveView( int position) { final int length = this .activeViews.length; if (position > length - 1 ) { getCount(position + 1 ); } return activeViews[position]; } (3)获取已回收的View对象。 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 /** 获取回收的view */ View getRecycleView( int position) { return retrieveFromRecycle(recycleViews, position); } /** 检索回收的view */ static View retrieveFromRecycle(SparseArray<View> recycleViews, int position) { int size = recycleViews.size(); if (size > 0 ) { // See if we still have a view for this position. for ( int i = 0 ; i < size; i++) { int fromPosition = recycleViews.keyAt(i); View view = recycleViews.get(fromPosition); if (fromPosition == position) { recycleViews.remove(fromPosition); return view; } } int index = size - 1 ; View r = recycleViews.valueAt(index); recycleViews.remove(recycleViews.keyAt(index)); return r; } else { return null ; } } 4.列表每隐藏一行,将消失的行布局对应的View对象回收,添加到recycleViews容器里,同时移除activeViews里的这个View。然后再进行比较并清除recycleViews容器里的回收对象,保证回收对象总数不多于活动view容器的总长度。 如下: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 // 隐藏 @Override public void onInvalidateItem( int id) { super .onInvalidateItem(id); // ..... // 回收view对象 View recycleView = mViewRecycler.getActiveView(id); if (recycleView != null ) { mViewRecycler.addRecycleView(id, recycleView); } } ViewRecycler类里的对应方法: 1 2 3 4 5 6 7 8 9 10 11 12 13 /** 添加废弃的view,无序添加 */ void addRecycleView( int position, View scrap) { recycleViews.put(position, scrap); final int length = this .activeViews.length; if (position < length) { this .activeViews[position] = null ; } pruneRecycleViews(); // Log.e("Recycle", "Recycle.size() = " +recycleViews.size()); } 1 2 3 4 5 6 7 8 9 10 11 12 /** 确保废弃的view总数不多于活动的view容器的长度(此方法可再改进为不多于当前活动的View对象数量) */ private void pruneRecycleViews() { final int maxViews = activeViews.length; int size = recycleViews.size(); final int extras = size - maxViews; size--; for ( int j = 0 ; j < extras; j++) { recycleViews.remove(recycleViews.keyAt(size--)); } } 5.退出时,清除所有View对象及其引用。 以下方法则是根据项目需求,将所有的活动view移到recycleViews里,再整理recycleViews。 如下： 1 2 3 4 5 6 7 @Override public void onDestroy() { super .onDestroy(); //销毁所有view对象 mViewRecycler.recycleAllActiveViews(); } ViewRecycler类里的对应方法: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 /** 将所有剩余的活动view移到废弃view里 */ void recycleAllActiveViews() { final View[] activeViews = this .activeViews; SparseArray<View> recycleViews = this .recycleViews; final int count = activeViews.length; for ( int i = count - 1 ; i >= 0 ; i--) { final View victim = activeViews[i]; if (victim != null ) { activeViews[i] = null ; recycleViews.put(i, victim); } } pruneRecycleViews(); } 二、调试结果 滑动时,请求加载行数据。每次添加一个行布局对象，当达到10行后开始执行View对象回收。每次将栈底的View回收并复用到栈顶的行布局里。如下图: 三、最后附上完整的ViewRecycler类 如下: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 public class ViewRecycler { private SparseArray<View> recycleViews; // 废弃的view private View[] activeViews = new View[ 0 ]; //正在使用的view public ViewRecycler() { recycleViews = new SparseArray<View>(); } /** 获取活动view的总数 */ public void getCount( int count) { final int length = this .activeViews.length; if (count > length) { final View[] activeViews = this .activeViews; this .activeViews = Arrays.copyOf(activeViews, count); // Log.e("getCount", "activeViews[" + (count - 1) + "]=" + this.activeViews[count-1]); } } /** 添加记录当前活动的view */ public void addActiveView( int position, View view) { final int length = this .activeViews.length; if (position > length - 1 ) { getCount(position + 1 ); } this .activeViews[position] = view; // Log.e("addActiveView", "activeViews.size() = " + Arrays.toString(activeViews)); } /** 获取某个活动view */ public View getActiveView( int position) { final int length = this .activeViews.length; if (position > length - 1 ) { getCount(position + 1 ); } return activeViews[position]; } /** 获取废弃的view */ View getRecycleView( int position) { return retrieveFromRecycle(recycleViews, position); } /** 检索废弃的view */ static View retrieveFromRecycle(SparseArray<View> recycleViews, int position) { int size = recycleViews.size(); if (size > 0 ) { // See if we still have a view for this position. for ( int i = 0 ; i < size; i++) { int fromPosition = recycleViews.keyAt(i); View view = recycleViews.get(fromPosition); if (fromPosition == position) { recycleViews.remove(fromPosition); return view; } } int index = size - 1 ; View r = recycleViews.valueAt(index); recycleViews.remove(recycleViews.keyAt(index)); return r; } else { return null ; } } /** 添加废弃的view,无序添加 */ void addRecycleView( int position, View scrap) { recycleViews.put(position, scrap); final int length = this .activeViews.length; if (position < length) { this .activeViews[position] = null ; } pruneRecycleViews(); // Log.e("Recycle", "Recycle.size() = " +recycleViews.size()); } /** 将所有剩余的活动view移到废弃view里 */ void recycleAllActiveViews() { final View[] activeViews = this .activeViews; SparseArray<View> recycleViews = this .recycleViews; final int count = activeViews.length; for ( int i = count - 1 ; i >= 0 ; i--) { final View victim = activeViews[i]; if (victim != null ) { activeViews[i] = null ; recycleViews.put(i, victim); } } pruneRecycleViews(); } /** 确保废弃的view不多于活动的view容器的总数量 */ private void pruneRecycleViews() { final int maxViews = activeViews.length; int size = recycleViews.size(); final int extras = size - maxViews; size--; for ( int j = 0 ; j < extras; j++) { recycleViews.remove(recycleViews.keyAt(size--)); } } } 方法仅供参考，具体实现过程还需根据项目实际需求进行修改或优化。欢迎各路高手不吝赐教,多多交流！ 本文转自 glblong 51CTO博客，原文链接：http://blog.51cto.com/glblong/1366319，如需转载请自行联系原作者
