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Android_异步加载2

程序开发 2023-09-03 15:37:03


         接着这篇博客写：http://blog.csdn.net/two_water/article/details/51477206

        异步加载1这篇博客在最后暴露出了一个问题，就是只在ListView的最后一个Item的ImageView刷新图片，解决问题的方案也提出来了，需要让url和对应的ImageView进行下配对！

ImageLoader的代码把showImageByThread方法里面的判断是否有缓存图片的代码注释了，改到在Adapter那里进行判断，判断是否有缓存图片，如果有显示缓存的图片，如果没有就先显示默认加载的图片，然后再去加载网络图片，并添加缓存！

package com.liangdianshui.asynchronouslyload;import android.content.Context;
 import android.graphics.Bitmap;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.BaseAdapter;
 import android.widget.ImageView;
 import android.widget.TextView;import java.util.List;/*** Created by 两点水 on 2016/5/12.*/
 public class MyAdapter extends BaseAdapter {private Context context;private List list;private ViewHolder mHolder;private ImageLoader mImaeLoader;public MyAdapter(Context context, List list) {this.context = context;this.list = list;mImaeLoader = new ImageLoader();  //因为创建了缓存空间，所以放在构造方法，只创建一次}@Overridepublic int getCount() {return list.size();}@Overridepublic Object getItem(int position) {return list.get(position);}@Overridepublic long getItemId(int position) {return position;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {if (convertView == null) {convertView = LayoutInflater.from(context).inflate(R.layout.item_layout, null);mHolder = new ViewHolder();mHolder.tvTitle = (TextView) convertView.findViewById(R.id.tv_title);mHolder.tvContent = (TextView) convertView.findViewById(R.id.tv_content);mHolder.ivIcon = (ImageView) convertView.findViewById(R.id.iv_icon);convertView.setTag(mHolder);} else {mHolder = (ViewHolder) convertView.getTag();}
 //		mHolder.ivIcon.setImageResource(R.mipmap.ic_launcher);//默认加载的图片String url = list.get(position).getDataIconUrl();mHolder.ivIcon.setTag(url);//为防止listview显示的图片错乱，重复，闪烁
 //		new ImageLoader().showImageByThread(mHolder.ivIcon, url);Bitmap bitmapFromCache = mImaeLoader.getBitmapFromCache(url);if (bitmapFromCache != null) {mHolder.ivIcon.setImageBitmap(bitmapFromCache);}else{mHolder.ivIcon.setImageResource(R.mipmap.ic_launcher);mImaeLoader.showImageByThread(mHolder.ivIcon, url);}mHolder.tvTitle.setText(list.get(position).getDataTitle());mHolder.tvContent.setText(list.get(position).getDataContent());return convertView;}class ViewHolder {private TextView tvTitle;private TextView tvContent;private ImageView ivIcon;}
 }
ImageLoader的代码： 

package com.liangdianshui.asynchronouslyload;import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.os.Handler;
 import android.os.Message;
 import android.util.LruCache;
 import android.widget.ImageView;import java.io.BufferedInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
 import java.net.MalformedURLException;
 import java.net.URL;/*** Created by 两点水 on 2016/5/22.*/
 public class ImageLoader {private ImageView mImageView;private String mUrl;private final int URL_BITMAP = 0;private LruCache mCache;   //使用Lru缓存（使用的Lru算法：近期最少使用算法）/*** 使用缓存肯定要先声明缓存空间，因此在构造方法中声明缓存空间*/public ImageLoader() {//获取程序最大使用的内存int maxMemory = (int) Runtime.getRuntime().maxMemory();int cacheSize = maxMemory / 4;  //缓存大小为最大缓存的四分之一//创建缓存，把缓存大小传进去mCache = new LruCache(cacheSize) {@Overrideprotected int sizeOf(String key, Bitmap value) {//每次存入缓存的时候都会调用这个方法，因此我们把图片的大小放进去return value.getByteCount();}};}/*** 把图片加入到缓存** @param url* @param bitmap*/public void addBitmapToCache(String url, Bitmap bitmap) {//LruCache好比是一个map，采用键值对的形式去保存图片if (getBitmapFromCache(url) == null) {//如果缓存中没有这个Bitmap，就把bitmap放进缓存mCache.put(url, bitmap);}}/*** 从缓存中获取图片** @param url*/public Bitmap getBitmapFromCache(String url) {return mCache.get(url); //根据url获取图片}Handler mHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);switch (msg.what) {case URL_BITMAP:
 //					if (mImageView.getTag().equals(mUrl)) {
 //						mImageView.setImageBitmap((Bitmap) msg.obj);
 //					}//因为传过来的对象更改了，这里也要跟着更改ImgHolder holder = (ImgHolder) msg.obj;if (holder.imageView.getTag().equals(holder.url)) {holder.imageView.setImageBitmap(holder.bitmap);}break;}}};/*** 多线程加载图片（Thread+Handler）* 根据url获取的itmap显示在ImageView中** @param imageView* @param url*/public void showImageByThread(final ImageView imageView, final String url) {mImageView = imageView;mUrl = url;//从缓存中取出图片
 //		Bitmap bitmap = getBitmapFromCache(url);//判断缓存中是否含有这张图片，没有的话去网络下载图片
 //		if (bitmap == null) {new Thread(new Runnable() {@Overridepublic void run() {Bitmap bitmap = getBitmapFromURL(url);//把下载下来的图片加到缓存中if (bitmap != null) {addBitmapToCache(url, bitmap);}Message message = new Message();
 //					message.obj = bitmap;//为了保证ImageView与这时候传递过来的图像一一对应的关系message.obj = new ImgHolder(imageView, bitmap, url);message.what = URL_BITMAP;mHandler.sendMessage(message);}}).start();  //记得start();
 //		} else {
 //			Message message = new Message();
 //			message.obj = bitmap;//为了保证ImageView与这时候传递过来的图像一一对应的关系
 //			message.obj = new ImgHolder(imageView, bitmap, url);
 //			message.what = URL_BITMAP;
 //			mHandler.sendMessage(message);
 //		}}/*** 根据rul获取bitmap** @param url* @return*/private Bitmap getBitmapFromURL(String url) {InputStream inputStream = null;try {URL urlBitmap = new URL(url);HttpURLConnection urlConnection = (HttpURLConnection) urlBitmap.openConnection();inputStream = new BufferedInputStream(urlConnection.getInputStream());Bitmap bitmap = BitmapFactory.decodeStream(inputStream);Thread.sleep(1000); //模拟网速慢的情况，为了更好的显示ImageView刷新多次的情况urlConnection.disconnect(); //关闭http连接return bitmap;} catch (MalformedURLException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} catch (InterruptedException e) {e.printStackTrace();} finally {try {inputStream.close(); //关闭流} catch (IOException e) {e.printStackTrace();}}return null;}/*** 新建一个类，记录ImageView，bitmap和url*/private class ImgHolder {public Bitmap bitmap;public ImageView imageView;public String url;public ImgHolder(ImageView iv, Bitmap bm, String url) {this.imageView = iv;this.bitmap = bm;this.url = url;}}}
效果图：


        使用AsyncTask实现上面的效果，其实AsyncTask也是根据多线程来实现的，因此基本的实现方式是一样的，直接贴代码：

package com.liangdianshui.asynchronouslyload;import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.os.AsyncTask;
 import android.os.Handler;
 import android.os.Message;
 import android.util.LruCache;
 import android.widget.ImageView;import java.io.BufferedInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
 import java.net.MalformedURLException;
 import java.net.URL;/*** Created by 两点水 on 2016/5/22.*/
 public class ImageLoader {private ImageView mImageView;private String mUrl;private final int URL_BITMAP = 0;private LruCache mCache;   //使用Lru缓存（使用的Lru算法：近期最少使用算法）/*** 使用缓存肯定要先声明缓存空间，因此在构造方法中声明缓存空间*/public ImageLoader() {//获取程序最大使用的内存int maxMemory = (int) Runtime.getRuntime().maxMemory();int cacheSize = maxMemory / 4;  //缓存大小为最大缓存的四分之一//创建缓存，把缓存大小传进去mCache = new LruCache(cacheSize) {@Overrideprotected int sizeOf(String key, Bitmap value) {//每次存入缓存的时候都会调用这个方法，因此我们把图片的大小放进去return value.getByteCount();}};}/*** 把图片加入到缓存** @param url* @param bitmap*/public void addBitmapToCache(String url, Bitmap bitmap) {//LruCache好比是一个map，采用键值对的形式去保存图片if (getBitmapFromCache(url) == null) {//如果缓存中没有这个Bitmap，就把bitmap放进缓存mCache.put(url, bitmap);}}/*** 从缓存中获取图片** @param url*/public Bitmap getBitmapFromCache(String url) {return mCache.get(url); //根据url获取图片}Handler mHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);switch (msg.what) {case URL_BITMAP:
 //					if (mImageView.getTag().equals(mUrl)) {
 //						mImageView.setImageBitmap((Bitmap) msg.obj);
 //					}//因为传过来的对象更改了，这里也要跟着更改ImgHolder holder = (ImgHolder) msg.obj;if (holder.imageView.getTag().equals(holder.url)) {holder.imageView.setImageBitmap(holder.bitmap);}break;}}};/*** 多线程加载图片（Thread+Handler）* 根据url获取的itmap显示在ImageView中** @param imageView* @param url*/public void showImageByThread(final ImageView imageView, final String url) {mImageView = imageView;mUrl = url;//从缓存中取出图片
 //		Bitmap bitmap = getBitmapFromCache(url);//判断缓存中是否含有这张图片，没有的话去网络下载图片
 //		if (bitmap == null) {new Thread(new Runnable() {@Overridepublic void run() {Bitmap bitmap = getBitmapFromURL(url);//把下载下来的图片加到缓存中if (bitmap != null) {addBitmapToCache(url, bitmap);}Message message = new Message();
 //					message.obj = bitmap;//为了保证ImageView与这时候传递过来的图像一一对应的关系message.obj = new ImgHolder(imageView, bitmap, url);message.what = URL_BITMAP;mHandler.sendMessage(message);}}).start();  //记得start();
 //		} else {
 //			Message message = new Message();
 //			message.obj = bitmap;//为了保证ImageView与这时候传递过来的图像一一对应的关系
 //			message.obj = new ImgHolder(imageView, bitmap, url);
 //			message.what = URL_BITMAP;
 //			mHandler.sendMessage(message);
 //		}}/*** 根据rul获取bitmap** @param url* @return*/private Bitmap getBitmapFromURL(String url) {InputStream inputStream = null;try {URL urlBitmap = new URL(url);HttpURLConnection urlConnection = (HttpURLConnection) urlBitmap.openConnection();inputStream = new BufferedInputStream(urlConnection.getInputStream());Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
 //			Thread.sleep(1000); //模拟网速慢的情况，为了更好的显示ImageView刷新多次的情况urlConnection.disconnect(); //关闭http连接return bitmap;} catch (MalformedURLException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {try {inputStream.close(); //关闭流} catch (IOException e) {e.printStackTrace();}}return null;}/*** 新建一个类，记录ImageView，bitmap和url*/private class ImgHolder {public Bitmap bitmap;public ImageView imageView;public String url;public ImgHolder(ImageView iv, Bitmap bm, String url) {this.imageView = iv;this.bitmap = bm;this.url = url;}}/*** 通过AsyncTask异步加载图片显示到ImageView** @param imageView* @param url*/public void showImageByAsyncTask(ImageView imageView, String url) {Bitmap bitmap = getBitmapFromCache(url);if (bitmap == null) {  //判断缓存是否有对应的图片new MyAsyncTask(imageView, url).execute(url);} else {imageView.setImageBitmap(bitmap);}}/*** 创建MyAsyncTask内部类* 通过AsyncTask异步加载图片*/private class MyAsyncTask extends AsyncTask {private ImageView mImageView;private String mUrl;/*** 创建构造方法初始化ImagaeView*/public MyAsyncTask(ImageView imageView, String url) {mImageView = imageView;mUrl = url;}@Overrideprotected void onPreExecute() {super.onPreExecute();}@Overrideprotected Bitmap doInBackground(String... params) {String url = params[0];Bitmap bitmap = getBitmapFromURL(url);if (bitmap != null) {addBitmapToCache(url, bitmap); //增叫图片到缓存}return bitmap;}@Overrideprotected void onPostExecute(Bitmap bitmap) {super.onPostExecute(bitmap);if (mImageView.getTag().equals(mUrl)) {mImageView.setImageBitmap(bitmap);}}}}
Adapter的代码： 

package com.liangdianshui.asynchronouslyload;import android.content.Context;
 import android.graphics.Bitmap;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.BaseAdapter;
 import android.widget.ImageView;
 import android.widget.TextView;import java.util.List;/*** Created by 两点水 on 2016/5/12.*/
 public class MyAdapter extends BaseAdapter {private Context context;private List list;private ViewHolder mHolder;private ImageLoader mImaeLoader;public MyAdapter(Context context, List list) {this.context = context;this.list = list;mImaeLoader = new ImageLoader();  //因为创建了缓存空间，所以放在构造方法，只创建一次}@Overridepublic int getCount() {return list.size();}@Overridepublic Object getItem(int position) {return list.get(position);}@Overridepublic long getItemId(int position) {return position;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {if (convertView == null) {convertView = LayoutInflater.from(context).inflate(R.layout.item_layout, null);mHolder = new ViewHolder();mHolder.tvTitle = (TextView) convertView.findViewById(R.id.tv_title);mHolder.tvContent = (TextView) convertView.findViewById(R.id.tv_content);mHolder.ivIcon = (ImageView) convertView.findViewById(R.id.iv_icon);convertView.setTag(mHolder);} else {mHolder = (ViewHolder) convertView.getTag();}
 //		mHolder.ivIcon.setImageResource(R.mipmap.ic_launcher);//默认加载的图片String url = list.get(position).getDataIconUrl();mHolder.ivIcon.setTag(url);//为防止listview显示的图片错乱，重复，闪烁
 //		new ImageLoader().showImageByThread(mHolder.ivIcon, url);/*** 注释多线程异步加载图片的代码*/
 //		Bitmap bitmapFromCache = mImaeLoader.getBitmapFromCache(url);
 //		if (bitmapFromCache != null) {
 //			mHolder.ivIcon.setImageBitmap(bitmapFromCache);
 //		} else {
 //			mHolder.ivIcon.setImageResource(R.mipmap.ic_launcher);
 //			mImaeLoader.showImageByThread(mHolder.ivIcon, url);
 //		}/***使用AsyncTask的方式实现多线程*/mHolder.ivIcon.setImageResource(R.mipmap.ic_launcher);//默认加载的图片mImaeLoader.showImageByAsyncTask(mHolder.ivIcon, url);mHolder.tvTitle.setText(list.get(position).getDataTitle());mHolder.tvContent.setText(list.get(position).getDataContent());return convertView;}class ViewHolder {private TextView tvTitle;private TextView tvContent;private ImageView ivIcon;}
 }

       效果图跟上面多线程实现的效果图是一样的！
ListView滚动时的高效优化：
           为什么要进行ListView滚动时的优化呢？当Item的界面很复杂的时候，我们的做法是一边滚动时还在加载图片的，加载完成后在主线程中更新ImageView，如果刚好在滚动的时候，更新ImageVIew，因为都是在主线程工作，这时候可能会有卡顿的现象！
       为了解决这种卡顿的现象，我们可以在用户滚动ListView的时候不更新ImageVeiw，只有当用户停止滚动的时候才更新，这样就不卡顿了！
       因此Adapter首先要监听滑动事件，在第一次加载的时候进行加载更新可见项item的视图，之后都是在ListView滑动停止的时候才更新加载图片，其余情况不加载图片！ 

package com.liangdianshui.asynchronouslyload;import android.content.Context;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.AbsListView;
 import android.widget.BaseAdapter;
 import android.widget.ImageView;
 import android.widget.ListView;
 import android.widget.TextView;import java.util.List;/*** Created by 两点水 on 2016/5/12.*/
 public class MyAdapter extends BaseAdapter implements AbsListView.OnScrollListener {private Context context;private List list;private ViewHolder mHolder;private ImageLoader mImaeLoader;private int mStart, mEnd;//当前可见项的起始位置public static String URLS[];//用于保存所有的图片URL地址private boolean mFirstIn;//用于判断是否首次启动预加载public MyAdapter(Context context, List list, ListView listView) {this.context = context;this.list = list;mFirstIn = true;mImaeLoader = new ImageLoader(listView);  //因为创建了缓存空间，所以放在构造方法，只创建一次//保存所有的图片URL地址URLS = new String[list.size()];for (int i = 0; i < URLS.length; i++) {URLS[i] = list.get(i).getDataIconUrl();}//实现listview滑动监听接口listView.setOnScrollListener(this);}@Overridepublic int getCount() {return list.size();}@Overridepublic Object getItem(int position) {return list.get(position);}@Overridepublic long getItemId(int position) {return position;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {if (convertView == null) {convertView = LayoutInflater.from(context).inflate(R.layout.item_layout, null);mHolder = new ViewHolder();mHolder.tvTitle = (TextView) convertView.findViewById(R.id.tv_title);mHolder.tvContent = (TextView) convertView.findViewById(R.id.tv_content);mHolder.ivIcon = (ImageView) convertView.findViewById(R.id.iv_icon);convertView.setTag(mHolder);} else {mHolder = (ViewHolder) convertView.getTag();}
 //		mHolder.ivIcon.setImageResource(R.mipmap.ic_launcher);//默认加载的图片String url = list.get(position).getDataIconUrl();mHolder.ivIcon.setTag(url);//为防止listview显示的图片错乱，重复，闪烁//		new ImageLoader().showImageByThread(mHolder.ivIcon, url);/*** 多线程异步加载图片*/
 //		Bitmap bitmapFromCache = mImaeLoader.getBitmapFromCache(url);
 //		if (bitmapFromCache != null) {
 //			mHolder.ivIcon.setImageBitmap(bitmapFromCache);
 //		} else {
 //			mHolder.ivIcon.setImageResource(R.mipmap.ic_launcher);
 //			mImaeLoader.showImageByThread(mHolder.ivIcon, url);
 //		}/***使用AsyncTask的方式实现多线程*/
 //        mHolder.ivIcon.setImageResource(R.mipmap.ic_launcher);//默认加载的图片mImaeLoader.showImageByAsyncTask(mHolder.ivIcon, url);mHolder.tvTitle.setText(list.get(position).getDataTitle());mHolder.tvContent.setText(list.get(position).getDataContent());return convertView;}@Overridepublic void onScrollStateChanged(AbsListView view, int scrollState) {//滚动状态为停止时，加载当前可见的数据项if (scrollState == SCROLL_STATE_IDLE) {mImaeLoader.loadPartImageView(mStart, mEnd);} else {//滑动没有停止时，停止任务mImaeLoader.CancelAllTask();}}@Overridepublic void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {mStart = firstVisibleItem;mEnd = firstVisibleItem + visibleItemCount;//首次启动预加载if (mFirstIn && visibleItemCount > 0) {mImaeLoader.loadPartImageView(mStart, mEnd);mFirstIn = false;}}class ViewHolder {private TextView tvTitle;private TextView tvContent;private ImageView ivIcon;}
 }
ImageLoader中写一个加载可见项视图Item的方法，然后修改下异步加载图片的方法： 

package com.liangdianshui.asynchronouslyload;import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.os.AsyncTask;
 import android.os.Handler;
 import android.os.Message;
 import android.util.LruCache;
 import android.widget.ImageView;
 import android.widget.ListView;import java.io.BufferedInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.HttpURLConnection;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.util.HashSet;
 import java.util.Set;/*** Created by 两点水 on 2016/5/22.*/
 public class ImageLoader {private ImageView mImageView;private String mUrl;private final int URL_BITMAP = 0;private LruCache mCache;   //使用Lru缓存（使用的Lru算法：近期最少使用算法）private ListView mlistView;private Set mTasks;/*** 使用缓存肯定要先声明缓存空间，因此在构造方法中声明缓存空间*/public ImageLoader(ListView listView) {this.mlistView = listView;mTasks = new HashSet<>();//获取程序最大使用的内存int maxMemory = (int) Runtime.getRuntime().maxMemory();int cacheSize = maxMemory / 4;  //缓存大小为最大缓存的四分之一//创建缓存，把缓存大小传进去mCache = new LruCache(cacheSize) {@Overrideprotected int sizeOf(String key, Bitmap value) {//每次存入缓存的时候都会调用这个方法，因此我们把图片的大小放进去return value.getByteCount();}};}/*** 把图片加入到缓存** @param url* @param bitmap*/public void addBitmapToCache(String url, Bitmap bitmap) {//LruCache好比是一个map，采用键值对的形式去保存图片if (getBitmapFromCache(url) == null) {//如果缓存中没有这个Bitmap，就把bitmap放进缓存mCache.put(url, bitmap);}}/*** 从缓存中获取图片** @param url*/public Bitmap getBitmapFromCache(String url) {return mCache.get(url); //根据url获取图片}Handler mHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);switch (msg.what) {case URL_BITMAP:
 //					if (mImageView.getTag().equals(mUrl)) {
 //						mImageView.setImageBitmap((Bitmap) msg.obj);
 //					}//因为传过来的对象更改了，这里也要跟着更改ImgHolder holder = (ImgHolder) msg.obj;if (holder.imageView.getTag().equals(holder.url)) {holder.imageView.setImageBitmap(holder.bitmap);}break;}}};/*** 多线程加载图片（Thread+Handler）* 根据url获取的itmap显示在ImageView中** @param imageView* @param url*/public void showImageByThread(final ImageView imageView, final String url) {mImageView = imageView;mUrl = url;//从缓存中取出图片
 //		Bitmap bitmap = getBitmapFromCache(url);//判断缓存中是否含有这张图片，没有的话去网络下载图片
 //		if (bitmap == null) {new Thread(new Runnable() {@Overridepublic void run() {Bitmap bitmap = getBitmapFromURL(url);//把下载下来的图片加到缓存中if (bitmap != null) {addBitmapToCache(url, bitmap);}Message message = new Message();
 //					message.obj = bitmap;//为了保证ImageView与这时候传递过来的图像一一对应的关系message.obj = new ImgHolder(imageView, bitmap, url);message.what = URL_BITMAP;mHandler.sendMessage(message);}}).start();  //记得start();
 //		} else {
 //			Message message = new Message();
 //			message.obj = bitmap;//为了保证ImageView与这时候传递过来的图像一一对应的关系
 //			message.obj = new ImgHolder(imageView, bitmap, url);
 //			message.what = URL_BITMAP;
 //			mHandler.sendMessage(message);
 //		}}/*** 根据rul获取bitmap** @param url* @return*/private Bitmap getBitmapFromURL(String url) {InputStream inputStream = null;try {URL urlBitmap = new URL(url);HttpURLConnection urlConnection = (HttpURLConnection) urlBitmap.openConnection();inputStream = new BufferedInputStream(urlConnection.getInputStream());Bitmap bitmap = BitmapFactory.decodeStream(inputStream);
 //			Thread.sleep(1000); //模拟网速慢的情况，为了更好的显示ImageView刷新多次的情况urlConnection.disconnect(); //关闭http连接return bitmap;} catch (MalformedURLException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {try {inputStream.close(); //关闭流} catch (IOException e) {e.printStackTrace();}}return null;}/*** 新建一个类，记录ImageView，bitmap和url*/private class ImgHolder {public Bitmap bitmap;public ImageView imageView;public String url;public ImgHolder(ImageView iv, Bitmap bm, String url) {this.imageView = iv;this.bitmap = bm;this.url = url;}}/*** 通过AsyncTask异步加载图片显示到ImageView** @param imageView* @param url*/public void showImageByAsyncTask(ImageView imageView, String url) {Bitmap bitmap = getBitmapFromCache(url);if (bitmap == null) {  //判断缓存是否有对应的图片
 //            new MyAsyncTask(imageView, url).execute(url);imageView.setImageResource(R.mipmap.ic_launcher);} else {imageView.setImageBitmap(bitmap);}}/*** 创建MyAsyncTask内部类* 通过AsyncTask异步加载图片*/private class MyAsyncTask extends AsyncTask {private ImageView mImageView;private String mUrl;/*** 创建构造方法初始化ImagaeView*/public MyAsyncTask(ImageView imageView, String url) {mImageView = imageView;mUrl = url;}public MyAsyncTask(String url) {mUrl = url;}@Overrideprotected void onPreExecute() {super.onPreExecute();}@Overrideprotected Bitmap doInBackground(String... params) {String url = params[0];Bitmap bitmap = getBitmapFromURL(url);if (bitmap != null) {addBitmapToCache(url, bitmap); //增叫图片到缓存}return bitmap;}@Overrideprotected void onPostExecute(Bitmap bitmap) {super.onPostExecute(bitmap);
 //            if (mImageView.getTag().equals(mUrl)) {
 //                mImageView.setImageBitmap(bitmap);
 //            }//从ListView中获取ImageviewImageView imageView = (ImageView) mlistView.findViewWithTag(mUrl);if (imageView != null && bitmap != null) {imageView.setImageBitmap(bitmap);}}}/*** 加载部分可见的图片*/public void loadPartImageView(int start, int end) {for (int i = start; i < end; i++) {String url = MyAdapter.URLS[i];//得到可见项目起始中的各个url//得到缓存中的BitmapBitmap bitmap = getBitmapFromCache(url);//bitmap为空就下载，非空就直接使用if (bitmap == null) {MyAsyncTask task = new MyAsyncTask(url);task.execute(url);mTasks.add(task);} else {//从ListView中获取ImageviewImageView imageView = (ImageView) mlistView.findViewWithTag(url);imageView.setImageBitmap(bitmap);}}}/*** 取消当前正在运行的所有任务*/public void CancelAllTask() {if (mTasks != null) {for (MyAsyncTask task :mTasks) {task.cancel(true);}}}}
Demo地址：http://download.csdn.net/detail/two_water/9540297





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