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activity_main.xml
<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"
tools:context="com.example.asynctask.MainActivity" >
<ListView
android:id="@+id/listview"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
</ListView>
</RelativeLayout><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="4dp" >
<ImageView
android:id="@+id/imageview"
android:layout_width="64dp"
android:layout_height="64dp"
android:src="@drawable/ic_launcher" />
<LinearLayout
android:gravity="center"
android:paddingLeft="4dp"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<TextView
android:id="@+id/tv_title"
android:layout_gravity="center"
android:text="title"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<TextView
android:id="@+id/tv_content"
android:layout_gravity="center"
android:text="content"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
</LinearLayout>
</LinearLayout>package com.example.asynctask;
import android.widget.ImageView;
public class NewsBean {
public String title;
public String content;
public String imageViewUrl;
public NewsBean() {
super();
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
public String getImageViewUrl() {
return imageViewUrl;
}
public void setImageViewUrl(String imageViewUrl) {
this.imageViewUrl = imageViewUrl;
}
}
package com.example.asynctask;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
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.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.ListView;
public class MainActivity extends Activity {
private ListView listView;
private static String httpUrl = "网址";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
listView = (ListView) findViewById(R.id.listview);
//开始异步任务进行异步加载
new NewAsyncTask().execute(httpUrl);
}
/**
* 异步任务--参数为url地址、没有进度、返回对象NewsBean集合
*/
class NewAsyncTask extends AsyncTask<String, Void, List<NewsBean>> {
private List<NewsBean> newBeanlist;
@Override
protected List<NewsBean> doInBackground(String... params) {
//通过http网址，进行获取json字符串获取的操作
return getJsonData(httpUrl);
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected void onPostExecute(List<NewsBean> result) {
super.onPostExecute(result);
}
@Override
protected void onProgressUpdate(Void... values) {
super.onProgressUpdate(values);
//获取完毕后，进行listview的数据适配操作，进行填充数据操作
NewAdapter adapter = new NewAdapter(newBeanlist, MainActivity.this,listView);
listView.setAdapter(adapter);
}
/**************************************************************
* 通过url地址信息，进行json字符串的获取
*/
private List<NewsBean> getJsonData(String url) {
//最终返回的json数据，解析，分装一个对象集合
newBeanlist = new ArrayList<NewsBean>();
/**
* 跟这个一样new URL(url).openConnection().getInputStream()
*/
try {
// 返回一个json字符串
String jsonString = readStream(new URL(url).openStream());
JSONObject jsonObject = null;
NewsBean newsBean;
try {
// 整体是一个jsonObject
jsonObject = new JSONObject(jsonString);
// 键是jsonArray数组
JSONArray jsonArray = jsonObject.getJSONArray("data");
// 从jsonArray中循环获取jsonObject
for (int i = 0; i < jsonArray.length(); i++) {
jsonObject = jsonArray.getJSONObject(i);
//创建本地的newsBean对象
newsBean = new NewsBean();
//为该对象进行属性值的设置操作
newsBean.imageViewUrl = jsonObject
.getString("picSmall");
newsBean.title = jsonObject.getString("name");
newsBean.content = jsonObject.getString("description");
//添加对象，组建集合
newBeanlist.add(newsBean);
}
} catch (JSONException e) {
e.printStackTrace();
}
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return newBeanlist;
}
/**
* 通过流的方式，读取的网络json字符串
*/
private String readStream(InputStream inStream) {
InputStreamReader isr;
String result = "";
try {
String line = "";
isr = new InputStreamReader(inStream, "utf-8");
BufferedReader br = new BufferedReader(isr);
while ((line = br.readLine()) != null) {
result += line;
}
} catch (Exception e) {
}
return result;
}
}
}
package com.example.asynctask;
import java.util.List;
import android.R.bool;
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 NewAdapter extends BaseAdapter implements OnScrollListener{
/**
* list是数据集合进行设置数据的操作
* layoutInflater进行加载itme布局
*
*/
private List<NewsBean> mList;
private LayoutInflater layoutInflater;
private ImageLoader mImageLoader;
//代表可见的条目的起始位置
private int mStart;
private int mEnd;
//将所有数据的url放到一个数组中，进行管理
public static String[] urls;
//代表是不是第一次启动程序--需要进行预加载图片
private boolean mFirst;
public NewAdapter(List<NewsBean> mList, Context context,ListView listView) {
super();
this.mList = mList;
this.layoutInflater = layoutInflater.from(context);
//将数据集合的url单独放到数组中
urls = new String[mList.size()];
mImageLoader = new ImageLoader(listView);
for (int i = 0; i < mList.size(); i++) {
//遍历获取每个条目的图片url地址信息
urls[i] = mList.get(i).imageViewUrl;
}
//默认是第一次加载
mFirst = true;
//注册监听
listView.setOnScrollListener(this);
}
@Override
public int getCount() {
return mList.size();
}
@Override
public Object getItem(int position) {
return mList.get(position);
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewHolder viewHolder = null;
if (convertView == null) {
viewHolder = new ViewHolder();
convertView = layoutInflater.inflate(R.layout.item, null);
viewHolder.title = (TextView) convertView
.findViewById(R.id.tv_title);
viewHolder.content = (TextView) convertView
.findViewById(R.id.tv_content);
viewHolder.imageView = (ImageView) convertView
.findViewById(R.id.imageview);
convertView.setTag(viewHolder);
} else {
viewHolder = (ViewHolder) convertView.getTag();
}
String imageViewUrl = mList.get(position).imageViewUrl;
//进行绑定--不会出现图片错位现象
viewHolder.imageView.setTag(imageViewUrl);
/**
* 进行图片加载的2种方式
*/
new ImageLoader().showImageByThread(viewHolder.imageView, mList.get(position).imageViewUrl);
mImageLoader.showImageByAsyncTask(viewHolder.imageView, imageViewUrl);
viewHolder.title.setText(mList.get(position).title);
viewHolder.content.setText(mList.get(position).content);
return convertView;
}
class ViewHolder {
public TextView title;
public TextView content;
public ImageView imageView;
}
/**
* 状态改变，进行调用,初始化不会被调用
*/
@Override
public void onScrollStateChanged(AbsListView view, int scrollState) {
if (scrollState == SCROLL_STATE_IDLE) {
//停止状态，进行加载图片
mImageLoader.loadImages(mStart, mEnd);
}else {
//停止所有的下载任务
mImageLoader.cancelAllTasks();
}
}
/**
* 滑动过程中调用---第一次加载就可以调用
*/
@Override
public void onScroll(AbsListView view, int firstVisibleItem,
int visibleItemCount, int totalItemCount) {
//获取listview可见的起始项目
mStart = firstVisibleItem;
mEnd = firstVisibleItem + visibleItemCount;
if (mFirst && visibleItemCount>0) {
//手动加载第一屏
mImageLoader.loadImages(mStart, mEnd);
mFirst = false;
}
}
}
package com.example.asynctask;
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.R.integer;
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;
// 图片缓存算法
private LruCache<String, Bitmap> mCache;
private ListView mListView;
private Set<NewsAsyncTask> mTasks;// ??
/**
* @param listView
*/
public ImageLoader(ListView listView) {
this.mListView = listView;
mTasks = new HashSet<ImageLoader.NewsAsyncTask>();
// 获取最大可用内存
int maxMemory = (int) Runtime.getRuntime().maxMemory();
int cacheSize = maxMemory / 4;
// 创建缓存
mCache = new LruCache<String, Bitmap>(cacheSize) {
@Override
protected int sizeOf(String key, Bitmap value) {
// 在每次存入缓存的时候，调用
return value.getByteCount();
}
};
}
/**
*
* @param imageView
* @param url
*/
public void showImageByAsyncTask(ImageView imageView, String url) {
// 获取图片时候，先从缓存取出对应的图片
Bitmap bitmap = getBitmapFromCache(url);
// 如果缓存中没有，就显示一个默认图片即可
if (bitmap == null) {
imageView.setImageResource(R.drawable.ic_launcher);
} else {
// 如果有的话，直接设置图片就可以了
imageView.setImageBitmap(bitmap);
}
}
/**
* 添加到缓存中
*/
public void addBitmapToCache(String url, Bitmap bitmap) {
// 如果某个url对应的图片不存在，为null,就直接存放即可
if (getBitmapFromCache(url) == null) {
mCache.put(url, bitmap);
}
}
/**
* 从缓存中取出图片--通过url获取图片
*/
public Bitmap getBitmapFromCache(String url) {
return mCache.get(url);
}
/**
* 加载了从start到end的图片的url
*/
public void loadImages(int start, int end) {
for (int i = start; i < end; i++) {
String url = NewAdapter.urls[i];
// 获取图片时候，先从缓存取出对应的图片
Bitmap bitmap = getBitmapFromCache(url);
// 如果缓存中没有，那么必须去下载
if (bitmap == null) {
NewsAsyncTask task = new NewsAsyncTask(url);
task.execute(url);
mTasks.add(task);
} else {
ImageView imageView = (ImageView) mListView
.findViewWithTag(url);
imageView.setImageBitmap(bitmap);
}
}
}
private class NewsAsyncTask extends AsyncTask<String, Void, Bitmap> {
private String url;
public NewsAsyncTask(String url) {
this.url = url;
}
@Override
protected Bitmap doInBackground(String... params) {
// 获取图片的url地址
String url = params[0];
// 从网络上获取图片
Bitmap bitmap = getBitmapFromUrl(url);
// 如果图片不为null
if (bitmap != null) {
// 加入到缓存中
addBitmapToCache(url, bitmap);
}
return bitmap;
// return getBitmapFromUrl(params[0]);
}
@Override
protected void onPostExecute(Bitmap result) {
super.onPostExecute(result);
ImageView imageView = (ImageView) mListView.findViewWithTag(url);
if (imageView != null && result != null) {
imageView.setImageBitmap(result);
}
}
}
/**
* 取消运行的任务
*/
public void cancelAllTasks() {
if (mTasks != null) {
for (NewsAsyncTask task : mTasks) {
task.cancel(false);
}
}
}
/****************************************************************
* 处理handler发送过来的消息--携带bitmap
*/
private Handler handler = new Handler() {
public void handleMessage(Message msg) {
if (mImageView.getTag().equals(mUrl)) {
// 处理消息
mImageView.setImageBitmap((Bitmap) msg.obj);
}
};
};
public ImageLoader() {
super();
}
/**
* @param imageView
* 图片视图
* @param url
* 图片的url地址
*/
public void showImageByThread(ImageView imageView, final String url) {
this.mImageView = imageView;
this.mUrl = url;
// 另开线程进行服务器的图片下载
new Thread() {
public void run() {
// 通过url获取图片
Bitmap bitmap = getBitmapFromUrl(url);
Message message = Message.obtain();
message.obj = bitmap;
// 通过handler发送消息
handler.sendMessage(message);
};
}.start();
}
/**
* 通过url获取网络图片
*
* @param urlString
* @return
*/
public Bitmap getBitmapFromUrl(String urlString) {
Bitmap bitmap = null;
InputStream inputStream = null;
try {
URL httpUrl = new URL(urlString);
HttpURLConnection connection = (HttpURLConnection) httpUrl
.openConnection();
inputStream = new BufferedInputStream(connection.getInputStream());
bitmap = BitmapFactory.decodeStream(inputStream);
connection.disconnect();
return bitmap;
} catch (Exception e) {
} finally {
try {
inputStream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return bitmap;
}
/**********************************************************
*
* @param imageView
* @param url
*/
}
版权声明：本文为博主原创文章，未经博主允许不得转载。
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原文地址：http://blog.csdn.net/u013210620/article/details/47218621
