接着这篇博客写：http://blog.youkuaiyun.com/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<DataBean> list;
private ViewHolder mHolder;
private ImageLoader mImaeLoader;
public MyAdapter(Context context, List<DataBean> 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
}
@Override
public int getCount() {
return list.size();
}
@Override
public Object getItem(int position) {
return list.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public 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;
}
}
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<String, Bitmap> 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<String, Bitmap>(cacheSize) {
@Override
protected 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() {
@Override
public 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() {
@Override
public 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;
}
}
}
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<String, Bitmap> 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<String, Bitmap>(cacheSize) {
@Override
protected 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() {
@Override
public 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() {
@Override
public 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<String, Void, Bitmap> {
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;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected 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;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
super.onPostExecute(bitmap);
if (mImageView.getTag().equals(mUrl)) {
mImageView.setImageBitmap(bitmap);
}
}
}
}
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<DataBean> list;
private ViewHolder mHolder;
private ImageLoader mImaeLoader;
public MyAdapter(Context context, List<DataBean> 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
}
@Override
public int getCount() {
return list.size();
}
@Override
public Object getItem(int position) {
return list.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public 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<DataBean> 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<DataBean> 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);
}
@Override
public int getCount() {
return list.size();
}
@Override
public Object getItem(int position) {
return list.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public 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;
}
@Override
public 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();
}
}
@Override
public 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;
}
}
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<String, Bitmap> 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<MyAsyncTask> 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<String, Bitmap>(cacheSize) {
@Override
protected 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() {
@Override
public 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() {
@Override
public 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<String, Void, Bitmap> {
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;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected 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;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
super.onPostExecute(bitmap);
// if (mImageView.getTag().equals(mUrl)) {
// mImageView.setImageBitmap(bitmap);
// }
//从ListView中获取Imageview
ImageView 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Bitmap
Bitmap 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Imageview
ImageView 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);
}
}
}
}
547
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