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:
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private
SparseArray<View> recycleViews;
// 废弃的view
private
View[] activeViews =
new
View[
0
];
//正在使用的view
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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:
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// 加载完毕
private
void
loadComplete()
{
//.....
mViewRecycler.getCount(mDataList.size());
}
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ViewRecycler类里的getCount方法:
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/** 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]);
}
}
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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:
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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);
}
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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。
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/** 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));
}
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(2)根据行号获取对应的View对象。
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/** 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];
}
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(3)获取已回收的View对象。
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/** 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
;
}
}
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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:
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// 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);
}
}
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ViewRecycler类里的对应方法:
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/** 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());
}
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/** 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--));
}
}
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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：
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@Override
public
void
onDestroy()
{
super
.onDestroy();
//销毁所有view对象
mViewRecycler.recycleAllActiveViews();
}
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ViewRecycler类里的对应方法:
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/** 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();
}
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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:
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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--));
}
}
}
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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
