标签：asynctask 异步 缓存 listview 内存
1，通过异步加载，避免阻塞UI线程
2，通过LruCache,将已经下载的图片放到内存中
3，通过判断Listview滑动状态，决定何时加载图片
4，不仅仅是listview ，任何控件都可以使用异步加载
代码结构：
布局1，
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<ListView
android:id="@+id/lv_main"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
</RelativeLayout>
布局2
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="40dp"
android:orientation="horizontal" >
<ImageView
android:id="@+id/iv_icon"
android:layout_width="64dp"
android:layout_height="64dp"
android:src="@drawable/ic_launcher"/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="4dp"
android:orientation="vertical">
<TextView
android:id="@+id/tv_title"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:textSize="15sp"
android:maxLines="1"
android:text="title"/>
<TextView
android:id="@+id/tv_content"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="10sp"
android:maxLines="3"
android:text="content"/>
</LinearLayout>
</LinearLayout>
java代码：
package com.my.listviewbaseadapter;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.util.Log;
import android.view.Menu;
import android.widget.ListView;
public class MainActivity extends Activity {
private ListView mListView;
private static String url = "http://www.**************************"; //一个含有图片，title，content三个内容的接口就行
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mListView = (ListView) findViewById(R.id.lv_main);
new NewsAsyncTask().execute(url);
}
/*
* 讲url对应的json格式数据转化为我们所封装的NewsBean对象
*/
private List<NewsBean> getJsonData(String url) {
List<NewsBean> newsBeanList = new ArrayList<NewsBean>();
try {
String jsonString = readStream(new URL(url).openStream());
JSONObject jsonObject;
NewsBean newsBean;
try {
jsonObject = new JSONObject(jsonString);
JSONArray jsonArray = jsonObject.getJSONArray("data");
for (int i = 0; i < jsonArray.length(); i++) {
jsonObject = jsonArray.getJSONObject(i);
newsBean = new NewsBean();
newsBean.newsIconUrl = jsonObject.getString("picSmall");
newsBean.newsTitle = jsonObject.getString("name");
newsBean.newsTitle = jsonObject.getString("description");
newsBeanList.add(newsBean);
}
} catch (Exception e) {
// TODO: handle exception
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return newsBeanList;
}
/*
* 通过InputStream解析网页返回的数据
*/
private String readStream(InputStream is) {
InputStreamReader isr;
String result = "";
try {
String line = "";
isr = new InputStreamReader(is, "utf-8");
BufferedReader br = new BufferedReader(isr);
while ((line = br.readLine()) != null) {
result += line;
}
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return result;
}
// AsyncTask<String, Void, Result>
/*
* 实现网络的异步访问
*
* AsyncTask<String, Void, Result>方法三个参数的含义 第一个参数String 是我们需要传入的url
* 第二个参数Void是记录中间的过程
* 第三个参数是我们返回的一个result，我们创建一个bean对象用于封装我们的json数据,最终返回的是Bean对象的集合
*/
class NewsAsyncTask extends AsyncTask<String, Void, List<NewsBean>> {
@Override
protected List<NewsBean> doInBackground(String... params) {
// TODO Auto-generated method stub
return getJsonData(params[0]);
}
@Override
protected void onPostExecute(List<NewsBean> newsBeans) {
// TODO Auto-generated method stub
super.onPostExecute(newsBeans);
NewsAdapter adapter = new NewsAdapter(MainActivity.this, newsBeans,mListView);
mListView.setAdapter(adapter);
}
}
}
package com.my.listviewbaseadapter;
import java.util.List;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.OnScrollListener;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
public class NeAdapter extends BaseAdapter implements OnScrollListener{
private List<NewsBean> mList;
private LayoutInflater mInflater;
private ImageLoader mImageLoader;
private int mStart,mEnd;
public static String[] URLS;
private boolean mFirstIn;
public NewsAdapter(Context context, List<NewsBean> data,ListView listview) {
super();
mList = data;
mInflater = LayoutInflater.from(context);
mImageLoader = new ImageLoader(listview);
URLS = new String[data.size()];
for (int i = 0; i < data.size(); i++) {
URLS[i] = data.get(i).newsIconUrl;
}
mFirstIn =true;
// 一定要注册对应的事件
listview.setOnScrollListener(this);
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return mList.size();
}
@Override
public Object getItem(int position) {
// TODO Auto-generated method stub
return mList.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return position;
}
class ViewHolder{
public ImageView ivIcon;
public TextView tvTitle,tvContent;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
ViewHolder viewHolder = null;
if (convertView == null) {
viewHolder = new ViewHolder();
convertView = mInflater.inflate(R.layout.item_layout, null);
viewHolder.ivIcon = (ImageView) convertView.findViewById(R.id.iv_icon);
viewHolder.tvTitle = (TextView) convertView.findViewById(R.id.tv_title);
viewHolder.tvContent = (TextView) convertView.findViewById(R.id.tv_content);
convertView.setTag(viewHolder);
}else {
viewHolder = (ViewHolder) convertView.getTag();
}
viewHolder.ivIcon.setImageResource(R.drawable.ic_launcher);
String url = mList.get(position).newsIconUrl;
viewHolder.ivIcon.setTag(url);
// new ImageLoader().showImageByThread(viewHolder.ivIcon, mList.get(position).newsIconUrl);
mImageLoader.showImageByAsyncTask(viewHolder.ivIcon, mList.get(position).newsIconUrl);
viewHolder.tvTitle.setText(mList.get(position).newsTitle);
viewHolder.tvContent.setText(mList.get(position).newsContent);
return convertView;
}
private ImageLoader mImageLoader() {
// TODO Auto-generated method stub
return null;
}
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
// TODO Auto-generated method stub
mStart = firstVisibleItem;
mEnd = firstVisibleItem + visibleItemCount;
// 第一次显示的时候调用
if (mFirstIn && visibleItemCount > 0) {
mImageLoader.loadImages(mStart, mEnd);
mFirstIn = false;
}
}
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
// TODO Auto-generated method stub
if (scrollState == SCROLL_STATE_IDLE) {
// 加载可见项
mImageLoader.loadImages(mStart, mEnd);
}else {
// 停止任务
mImageLoader.cancelAllTasks();
}
}
}
package com.my.listviewbaseadapter;
public class NeBean {
/*
* 封装我们需要的三个参数
* 1.iamge图片
* 2.title
* 3.content
* */
public String newsIconUrl;
public String newsTitle;
public String newsContent;
}
package com.my.listviewbaseadapter;
import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.HashSet;
import java.util.Set;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Handler;
import android.os.Message;
import android.support.v4.util.LruCache;
import android.widget.ImageView;
import android.widget.ListView;
public class ImageLoader {
private ImageView mImageView;
private String mUrl;
// 创建cache
private LruCache<String, Bitmap> mCaches;
private ListView mListView;
private Set<NewsAsyncTask> mTask;
public ImageLoader(ListView listview){
mListView = listview;
mTask = new HashSet<ImageLoader.NewsAsyncTask>();
int maxMemorty = (int) Runtime.getRuntime().maxMemory();
int cacheSize = maxMemorty / 4;
mCaches = new LruCache<String, Bitmap>(cacheSize){
@Override
protected int sizeOf(String key, Bitmap value) {
// TODO Auto-generated method stub
// 每次存入缓存的时候调用
return value.getByteCount();
}
};
}
//增加到缓存
public void addBitmapToCache(String url,Bitmap bitmap){
if (getBitmapForURL(url) == null) {
mCaches.put(url, bitmap);
}
}
// 从缓存中获取数据
public Bitmap getBitmapFromCache(String url){
return mCaches.get(url);
}
private Handler mHandler = new Handler() {
public void handleMessage(Message msg) {
super.handleMessage(msg);
if (mImageView.getTag().equals(mUrl)){
mImageView.setImageBitmap((Bitmap)msg.obj);
}
}
};
public void showImageByThread(ImageView imageview, final String url) {
mImageView = imageview;
mUrl = url;
new Thread() {
@Override
public void run() {
// TODO Auto-generated method stub
super.run();
Bitmap bitmap = getBitmapForURL(url);
Message message = Message.obtain();
message.obj = bitmap;
mHandler.sendMessage(message);
}
}.start();
}
public Bitmap getBitmapForURL(String urlString) {
Bitmap bitmap;
InputStream is = null;
try {
URL url = new URL(urlString);
HttpURLConnection connection = (HttpURLConnection) url
.openConnection();
is = new BufferedInputStream(connection.getInputStream());
bitmap = BitmapFactory.decodeStream(is);
connection.disconnect();
return bitmap;
} catch (Exception e) {
// TODO: handle exception
} finally {
try {
is.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return null;
}
public void showImageByAsyncTask(ImageView imageview, String url) {
// 从缓存中取出对应的图片
Bitmap bitmap = getBitmapFromCache(url);
// 如果缓存中没有，就必须到网络上获取图片
if (bitmap == null) {
imageview.setImageResource(R.drawable.ic_launcher);
}else {
imageview.setImageBitmap(bitmap);
}
}
public void cancelAllTasks(){
if (mTask != null) {
for (NewsAsyncTask task : mTask) {
task.cancel(false);
}
}
}
public void loadImages(int start,int end){
for (int i = start; i < end; i++) {
String url = NewsAdapter.URLS[i];
// 从缓存中取出对应的图片
Bitmap bitmap = getBitmapFromCache(url);
// 如果缓存中没有，就必须到网络上获取图片
if (bitmap == null) {
NewsAsyncTask task = new NewsAsyncTask(url);
task.execute(url);
mTask.add(task);
}else {
ImageView imageView = (ImageView) mListView.findViewWithTag(url);
}
}
}
private class NewsAsyncTask extends AsyncTask<String, Void, Bitmap> {
// private ImageView mImageView;
private String mUrl;
@SuppressWarnings("unused")
public NewsAsyncTask(String url) {
// mImageView = imageView;
mUrl = url;
}
@Override
protected Bitmap doInBackground(String... params) {
// TODO Auto-generated method stub
String url = params[0];
// 从网络获取图片
Bitmap bitmap = getBitmapForURL(params[0]);
if (bitmap != null) {
// 将不再缓存的图片加入缓存，从而实现缓存的效果
addBitmapToCache(url, bitmap);
}
return bitmap;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
// TODO Auto-generated method stub
super.onPostExecute(bitmap);
// if (mImageView.getTag().equals(mUrl)) {
// mImageView.setImageBitmap(bitmap);
// }
ImageView imageView = (ImageView) mListView.findViewWithTag(mUrl);
if (imageView != null && bitmap != null) {
imageView.setImageBitmap(bitmap);
}
}
}
}
源码下载地址：http://download.csdn.net/detail/weimo1234/8806235
listview+BaseAdapter + AsyncTask异步请求网络 + LruCache缓存图片
标签：asynctask 异步 缓存 listview 内存
原文地址：http://blog.csdn.net/weimo1234/article/details/46495649
