图片异步加载AsyncTask以及ListView中item加载图片缓存

当LIstView加载多张图片时使用Handler+Runnable有点不现实，，可以用谷歌的AsyncTask，另外，如果所需加载的图片不需要很精细的控制的话也可以采用AsyncTask，还有就是Listview加载的图片将其存入缓存中，暂且没写将其存在sd卡中，如果每次刷新Listview都要加载图片那么用户体验和程序的性能，下面附上代码：

SingleImageTaskUtil.java单个或者多个不要求对图片进行精细操作的话可以使用此工具类

package com.loulijun.utils;import java.io.IOException;import java.io.InputStream;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.AsyncTask;import android.support.v4.util.LruCache;import android.widget.ImageView;public class SingleImageTaskUtil extends AsyncTask<String, Void, Bitmap> {private ImageView iv;public SingleImageTaskUtil(ImageView iv) {this.iv = iv;}@Overrideprotected Bitmap doInBackground(String… params) {// TODO Auto-generated method stubBitmap bitmap = null;try {bitmap = SimpleImageLoader.getBitmap(params[0]);} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}return bitmap;}@Overrideprotected void onPostExecute(Bitmap result) {// TODO Auto-generated method stubsuper.onPostExecute(result);if (result != null) {iv.setImageBitmap(result);}}@Overrideprotected void onPreExecute() {// TODO Auto-generated method stubsuper.onPreExecute();}public static class SimpleImageLoader {public static Bitmap getBitmap(String urlStr) throws IOException {Bitmap bitmap;URL url = new URL(urlStr);HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setRequestMethod("GET");//用户可以根据不同的需要选择不同的方法get或者post请求conn.setReadTimeout(5 * 1000);conn.setDoInput(true);conn.connect();InputStream is = conn.getInputStream();bitmap = BitmapFactory.decodeStream(is);is.close();return bitmap;}}}

ListViewImageTaskUtil.java当用户选择加载图片到Listview中可以选择此工具类操作，下面附上工具里代码，以及Listview的Adapter中的操作代码

package com.loulijun.utils;import java.io.IOException;import java.io.InputStream;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.os.AsyncTask;import android.support.v4.util.LruCache;import android.widget.ImageView;public class ListViewImageTaskUtil extends AsyncTask<String, Void, Bitmap> {private ImageView iv;private LruCache<String, Bitmap> lruCache;//定义一个缓存区，程序被系统分配的public ListViewImageTaskUtil(ImageView iv) {this.iv = iv;}public ListViewImageTaskUtil(ImageView iv, LruCache<String, Bitmap> lruCache) {super();this.iv = iv;this.lruCache = lruCache;}@Overrideprotected Bitmap doInBackground(String… params) {// TODO Auto-generated method stubBitmap bitmap = null;try {bitmap = SimpleImageLoader.getBitmap(params[0]);} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}addBitmapToMemoryCache(params[0], bitmap);return bitmap;}@Overrideprotected void onPostExecute(Bitmap result) {// TODO Auto-generated method stubsuper.onPostExecute(result);if (result != null) {iv.setImageBitmap(result);}}@Overrideprotected void onPreExecute() {// TODO Auto-generated method stubsuper.onPreExecute();}private void addBitmapToMemoryCache(String key, Bitmap bitmap) {if (getBitmapFromMemoryCache(key) == null) {lruCache.put(key, bitmap);}}public Bitmap getBitmapFromMemoryCache(String key) {return lruCache.get(key);}public static class SimpleImageLoader {public static Bitmap getBitmap(String urlStr) throws IOException {Bitmap bitmap;URL url = new URL(urlStr);HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setRequestMethod("GET");conn.setReadTimeout(5 * 1000);conn.setDoInput(true);conn.connect();InputStream is = conn.getInputStream();bitmap = BitmapFactory.decodeStream(is);is.close();return bitmap;}}}

MyAdapter.java下面是Adapter代码

package com.loulijun.adapter;import java.util.List;import android.content.Context;import android.graphics.Bitmap;import android.support.v4.util.LruCache;import android.view.LayoutInflater;import android.view.View;import android.view.ViewGroup;import android.widget.BaseAdapter;import android.widget.Button;import android.widget.ImageView;import android.widget.TextView;import android.widget.Toast;import com.loulijun.bean.CommondBean;import com.loulijun.logindemo.R;import com.loulijun.utils.ListViewImageTaskUtil;public class MyAdapter extends BaseAdapter {private Context context;private List<CommondBean> commondBeans;// 获取当前应用程序所分配的最大内存private final int maxMemory = (int) Runtime.getRuntime().maxMemory();// 只用五分之一用来做图片缓存private final int cacheSize = maxMemory / 5;private LruCache<String, Bitmap> mLruCache = new LruCache<String, Bitmap>(cacheSize) {// 重写sizeof（）方法@Overrideprotected int sizeOf(String key, Bitmap bitmap) {// TODO Auto-generated method stub// 这里用多少kb来计算return bitmap.getRowBytes() * bitmap.getHeight() / 1024;}};public MyAdapter(Context context, List<CommondBean> commondBeans) {this.context = context;this.commondBeans = commondBeans;}@Overridepublic int getCount() {// TODO Auto-generated method stubreturn commondBeans.size();}@Overridepublic Object getItem(int position) {// TODO Auto-generated method stubreturn commondBeans.get(position);}@Overridepublic long getItemId(int position) {// TODO Auto-generated method stubreturn position;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {// TODO Auto-generated method stubView view = convertView;ViewHolder holder = null;if (view == null) {view = LayoutInflater.from(context).inflate(R.layout.item_listview_commond, null);holder = new ViewHolder();view.setTag(holder);holder.user_img = (ImageView) view.findViewById(R.id.userimg);holder.user_detail = (TextView) view.findViewById(R.id.detail);holder.user_name = (TextView) view.findViewById(R.id.name);holder.user_good = (Button) view.findViewById(R.id.good);holder.user_good.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubToast.makeText(context, "32个赞！", Toast.LENGTH_SHORT).show();}});holder.user_poor = (Button) view.findViewById(R.id.poor);holder.user_poor.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubToast.makeText(context, "贬低一个！", Toast.LENGTH_SHORT).show();}});holder.user_hot = (Button) view.findViewById(R.id.hot);holder.user_hot.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubToast.makeText(context, "更加火爆！", Toast.LENGTH_SHORT).show();}});holder.user_share = (Button) view.findViewById(R.id.share);holder.user_share.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubToast.makeText(context, "分享成功！", Toast.LENGTH_SHORT).show();}});holder.good = (TextView) view.findViewById(R.id.goodtext);holder.poor = (TextView) view.findViewById(R.id.poortext);holder.hot = (TextView) view.findViewById(R.id.hottext);holder.share = (TextView) view.findViewById(R.id.sharetext);} else {holder = (ViewHolder) convertView.getTag();}holder.user_detail.setText(commondBeans.get(position).getUserDetail());holder.user_name.setText(commondBeans.get(position).getUserName());holder.good.setText(commondBeans.get(position).getGood());holder.poor.setText(commondBeans.get(position).getPoor());holder.hot.setText(commondBeans.get(position).getHot());holder.share.setText(commondBeans.get(position).getShare());// 多任务处理加载图片// ListViewImageTaskUtil imageTask = new ListViewImageTaskUtil(holder.user_img);// imageTask.execute(commondBeans.get(position).getUserImg());loadBitmap(commondBeans.get(position).getUserImg(), holder.user_img);return view;}static class ViewHolder {ImageView user_img;TextView user_name;TextView user_detail;TextView good;TextView poor;TextView hot;TextView share;Button user_good;Button user_poor;Button user_hot;Button user_share;}private void loadBitmap(String urlStr, ImageView image) {ListViewImageTaskUtil asyncLoader = new ListViewImageTaskUtil(image, mLruCache);// 一个异步图片加载对象Bitmap bitmap = asyncLoader.getBitmapFromMemoryCache(urlStr);// 首先从内存缓存中获取图片if (bitmap != null) {image.setImageBitmap(bitmap);// 如果缓存中存在这张图片则直接设置给ImageView} else {image.setImageResource(R.drawable.dufu);// 否则先设置成默认的图片asyncLoader.execute(urlStr);// 然后执行异步任务AsycnTask 去网上加载图片}}}

这两个工具类可以满足大部分的需求，如需对图片进行更为精细的操作大家可以自定义handler+Runnable

奢侈地享受旅不问人，行随己意的潇洒。