本文提出的优化方法是:在getView()构建一个View列表(List<View>),把最近构建的View存起来,回退时直接从View列表中读取,而不是动态构建。使用这种方法有2个好处:
1.快速读取过去的Item;
2.直接保存View而不是Bitmap,避免了ImageView.setImageBitmaps()带来的延时。
当然坏处就是浪费内存,所以要设定一个上限,超过了就删掉最老的Item。
“CacheAdapter 缓存50个Item”比ViewHolderAdapter的速度略快,“CacheAdapter 缓存75个Item”依然是最快的。
总结:“CacheAdapter 缓存50个Item”速度与HolderView略快,读取最近的Item速度最快,缓存的Item越多速度越快。“CacheAdapter 缓存75个Item”占用内存最少,这是由于一部分图片下载失败,保存的Item的图片为空,实际上是缓存越多Item占用的内存越多。
CacheAdapter.java是实现缓存Item的自定义Adapter,源码如下:
java代码:
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/**
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* 使用列表缓存过去的Item
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* @author hellogv
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*
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*/
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public class CacheAdapter extends BaseAdapter {
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public class Item {
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public String itemImageURL;
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public String itemTitle;
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public Item(String itemImageURL, String itemTitle) {
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this.itemImageURL = itemImageURL;
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this.itemTitle = itemTitle;
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}
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}
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private Context mContext;
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private ArrayList<Item> mItems = new ArrayList<Item>();
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LayoutInflater inflater;
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public CacheAdapter(Context c) {
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mContext = c;
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inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
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}
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public void addItem(String itemImageURL, String itemTitle) {
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mItems.add(new Item(itemImageURL, itemTitle));
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}
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public int getCount() {
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return mItems.size();
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}
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public Item getItem(int position) {
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return mItems.get(position);
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}
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public long getItemId(int position) {
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return position;
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}
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List<Integer> lstPosition=new ArrayList<Integer>();
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List<View> lstView=new ArrayList<View>();
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List<Integer> lstTimes= new ArrayList<Integer>();
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long startTime=0;
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public View getView(int position, View convertView, ViewGroup parent) {
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startTime=System.nanoTime();
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if (lstPosition.contains(position) == false) {
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if(lstPosition.size()>75)//这里设置缓存的Item数量
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{
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lstPosition.remove(0);//删除第一项
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lstView.remove(0);//删除第一项
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}
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convertView = inflater.inflate(R.layout.item, null);
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TextView text = (TextView) convertView.findViewById(R.id.itemText);
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ImageView icon = (ImageView) convertView.findViewById(R.id.itemImage);
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text.setText(mItems.get(position).itemTitle);
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new AsyncLoadImage().execute(new Object[] { icon,mItems.get(position).itemImageURL });
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lstPosition.add(position);//添加最新项
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lstView.add(convertView);//添加最新项
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} else {
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convertView = lstView.get(lstPosition.indexOf(position));
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}
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int endTime=(int) (System.nanoTime()-startTime);
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lstTimes.add(endTime);
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if(lstTimes.size()==10)
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{
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int total=0;
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for(int i=0;i<lstTimes.size();i++)
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total=total+lstTimes.get(i);
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Log.e("10个所花的时间:" +total/1000 +" μs", "所用内存:"+Runtime.getRuntime().totalMemory()/1024 +" KB");
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lstTimes.clear();
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}
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return convertView;
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}
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/**
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* 异步读取网络图片
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* @author hellogv
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*/
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class AsyncLoadImage extends AsyncTask<Object, Object, Void> {
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@Override
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protected Void doInBackground(Object... params) {
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try {
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ImageView imageView=(ImageView) params[0];
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String url=(String) params[1];
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Bitmap bitmap = getBitmapByUrl(url);
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publishProgress(new Object[] {imageView, bitmap});
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} catch (MalformedURLException e) {
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Log.e("error",e.getMessage());
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e.printStackTrace();
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} catch (IOException e) {
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Log.e("error",e.getMessage());
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e.printStackTrace();
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}
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return null;
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}
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protected void onProgressUpdate(Object... progress) {
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ImageView imageView = (ImageView) progress[0];
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imageView.setImageBitmap((Bitmap) progress[1]);
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}
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}
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static public Bitmap getBitmapByUrl(String urlString)
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throws MalformedURLException, IOException {
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URL url = new URL(urlString);
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URLConnection connection = url.openConnection();
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connection.setConnectTimeout(25000);
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connection.setReadTimeout(90000);
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Bitmap bitmap = BitmapFactory.decodeStream(connection.getInputStream());
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return bitmap;
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}
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其中if(lstPosition.size()>75)是设置缓存的Item数量的关键地方,这里缓存75个Item。
ViewHolderAdapter.java是实现ViewHolder加载Item的自定义Adapter,源码如下:
java代码:
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/**
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* 使用ViewHolder加载Item
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* @author hellogv
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*
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*/
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public class ViewHolderAdapter extends BaseAdapter {
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public class Item {
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public String itemImageURL;
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public String itemTitle;
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public Item(String itemImageURL, String itemTitle) {
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this.itemImageURL = itemImageURL;
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this.itemTitle = itemTitle;
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}
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}
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private Context mContext;
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private ArrayList<Item> mItems = new ArrayList<Item>();
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LayoutInflater inflater;
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public ViewHolderAdapter(Context c) {
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mContext = c;
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inflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
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}
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public void addItem(String itemImageURL, String itemTitle) {
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mItems.add(new Item(itemImageURL, itemTitle));
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}
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public int getCount() {
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return mItems.size();
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}
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public Item getItem(int position) {
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return mItems.get(position);
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}
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public long getItemId(int position) {
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return position;
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}
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static class ViewHolder {
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TextView text;
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ImageView icon;
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}
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List<Integer> lstTimes= new ArrayList<Integer>();
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long startTime=0;
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public View getView(int position, View convertView, ViewGroup parent) {
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startTime=System.nanoTime();
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ViewHolder holder;
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if (convertView == null) {
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convertView = inflater.inflate(R.layout.item, null);
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holder = new ViewHolder();
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holder.text = (TextView) convertView.findViewById(R.id.itemText);
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holder.icon = (ImageView) convertView.findViewById(R.id.itemImage);
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convertView.setTag(holder);
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} else {
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holder = (ViewHolder) convertView.getTag();
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}
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holder.text.setText(mItems.get(position).itemTitle);
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new AsyncLoadImage().execute(new Object[]{holder.icon,mItems.get(position).itemImageURL });
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int endTime=(int) (System.nanoTime()-startTime);
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lstTimes.add(endTime);
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if(lstTimes.size()==10) {
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int total=0;
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for(int i=0;i<lstTimes.size();i++)
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total=total+lstTimes.get(i);
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Log.e("10个所花的时间:" +total/1000 +" μs",
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"所用内存:"+Runtime.getRuntime().totalMemory()/1024 +" KB");
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lstTimes.clear();
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}
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return convertView;
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}
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/**
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* 异步读取网络图片
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* @author hellogv
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*/
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class AsyncLoadImage extends AsyncTask<Object, Object, Void> {
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@Override
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protected Void doInBackground(Object... params) {
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try {
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ImageView imageView=(ImageView) params[0];
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String url=(String) params[1];
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Bitmap bitmap = CacheAdapter.getBitmapByUrl(url);
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publishProgress(new Object[] {imageView, bitmap});
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} catch (MalformedURLException e) {
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e.printStackTrace();
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} catch (IOException e) {
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e.printStackTrace();
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}
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return null;
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}
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protected void onProgressUpdate(Object... progress) {
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ImageView imageView = (ImageView) progress[0];
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imageView.setImageBitmap((Bitmap) progress[1]);
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}
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}
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testPerformance.java是主程序,通过注释符就可以分别测试CacheAdapter与ViewHolderAdapter的性能,源码如下:
java代码:
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public class testPerformance extends Activity {
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/** Called when the activity is first created. */
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@Override
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public void onCreate(Bundle savedInstanceState) {
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super.onCreate(savedInstanceState);
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setContentView(R.layout.main);
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this.setTitle("android平板上的GridView视图缓存优化-----hellogv");
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GridView gridview = (GridView) findViewById(R.id.gridview);
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CacheAdapter adapter=new CacheAdapter(this);
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// ViewHolderAdapter adapter=new ViewHolderAdapter(this);
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gridview.setAdapter(adapter);
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String urlImage="";//请自己选择网络上的静态图片
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for(int i=0;i<100;i++)
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{
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adapter.addItem(urlImage, "第"+i+"项");
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}
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}
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- }
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