解析Json并异步加载数据新闻信息(包括新闻图片)

代码运行实例效果

MainActivity.java

package io.github.deligencc.asynctask;

import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.ListView;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private ListView mListView;

    //请求的网址
    private static String URL = "http://www.imooc.com/api/teacher?type=4&num=30";


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mListView = (android.widget.ListView) findViewById(R.id.lv_main);
        new NewsAsyncTask().execute(URL);
    }

    /**
     * 实现网络的异步访问
     */
    public class NewsAsyncTask extends AsyncTask<String, Void, List<NewsBean>> {

        @Override
        protected List<NewsBean> doInBackground(String... params) {
            return getJsonData(params[0]);
        }

        @Override
        protected void onPostExecute(List<NewsBean> newsBeen) {
            super.onPostExecute(newsBeen);
            NewsAdapter adapter = new NewsAdapter(MainActivity.this, newsBeen,mListView);
            mListView.setAdapter(adapter);
        }
    }

    /**
     * 将url对应的jsdon个数数据转化为我们所封装的NewsBean
     * 解析Json数据 封装到List中
     *
     * @param url
     * @return
     */
    private List<NewsBean> getJsonData(String url) {
        List<NewsBean> newsBeanList = new ArrayList<>();
        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.newsContent = jsonObject.getString("description");
                    newsBeanList.add(newsBean);
                    Log.d("Tag","newsBeanList.size() is the "+newsBeanList.size());
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

            Log.d("xys", "jsonString");
        } catch (Exception e) {
            e.printStackTrace();
        }
        return newsBeanList;
    }

    /**
     * 通过InputStream is 解析网页返回数据
     *
     * @param is
     * @return
     */
    private String readStream(InputStream is) {
        InputStreamReader isr;
        String result = "";
        try {
            String line = "";
            isr = new InputStreamReader(is, "utf-8"); //字节流转化为字符流
            BufferedReader br = new BufferedReader(isr);
            while ((line = br.readLine()) != null) {
                result += line;
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }
}

图片异步加载类

ImageLoader.java

package io.github.deligencc.asynctask;

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.URL;
import java.util.HashSet;
import java.util.Set;

/**
 * Created by bummer on 2017/8/23.
 */

public class ImageLoader {

    private ImageView mImageView;

    private String mUrl;

    //创建Cache
    private LruCache<String, Bitmap> mCaches;//需要保存缓存对象的名字,保存对象  本质是map

    private ListView mListView;

    private Set<NewsAsyncTask> mTasks;

    public ImageLoader(ListView listView) {
        mListView = listView;
        mTasks = new HashSet<>();
        //获取最大可用内存
        int maxMemory = (int) Runtime.getRuntime().maxMemory();
        int cacheSize = maxMemory / 4;
        mCaches = new LruCache<String, Bitmap>(cacheSize) {
            @Override
            protected int sizeOf(String key, Bitmap value) {
                //返回图片大小，每次存入缓存时调用
                return value.getByteCount(); //将bitmap的实际大小传入
            }
        }; //初始化缓存大小
    }

    /**
     * 将内容保存的Cache
     */
    public void addBitmapToCache(String url, Bitmap bitmap) {
        if (getBitmapFromCache(url) == null) { //判断当前缓存是否存在
            mCaches.put(url, bitmap);
        }
    }

    /**
     * 从Cache中读取内容
     */
    public Bitmap getBitmapFromCache(String url) {
        //从缓存中获取数据
        return mCaches.get(url);
    }

    private Handler mhandler = new Handler() {
        @Override
        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(new Runnable() {
            @Override
            public void run() {
                Bitmap bitmap = getBitmapFromUrl(url);
                Message message = Message.obtain(); //通过这种方式创建的message,可以使用现有的,已经回收到的message,提高message的使用效率
                message.obj = bitmap;
                mhandler.sendMessage(message);

            }
        }).start();
    }

    public Bitmap getBitmapFromUrl(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();
//            Thread.sleep(1000);
            return bitmap;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    public void showImageByAsyncTask(ImageView imageView, String url) {
        //先判断缓存中是否存在数据，减少下载时间  从缓存中取出对应的图片
        Bitmap bitmap = getBitmapFromCache(url);
        if (bitmap == null) { //如果缓存中没有，必须从网络下载
            //new NewsAsyncTask(url).execute(url);
            imageView.setImageResource(R.mipmap.ic_launcher);
        } else { //直接从内存中获取 并设置
            imageView.setImageBitmap(bitmap);
        }
    }

    /**
     * 用来加载从start到end所有图片
     * @param start
     * @param end
     */
    public void loadImages(int start, int end) {
        for (int i = start; i < end; i++) {
            //从缓存中取出从start到end位置对应的图片
            String url = NewsAdapter.URLS[i];
            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);
            }
        }
    }

    /**
     * 取消当前正在取消的任务
     */
    public void cancelAllTasks() {
        if (mTasks != null) {
            for (NewsAsyncTask task : mTasks) {
               task.cancel(true);
            }
        }
    }

    private class NewsAsyncTask extends AsyncTask<String, Void, Bitmap> {

        private ImageView mImageView;
        private String mUrl;

        public NewsAsyncTask(String url) {
            //  mImageView = imageView;
            mUrl = url;
        }
        

        @Override
        protected Bitmap doInBackground(String... params) {
            String url = params[0];
            //将下载的图片保存缓存中 从网络获取图片
            Bitmap bitmap = getBitmapFromUrl(url);
            if (bitmap != null) {
                //将不再缓存的图片加入缓存
                addBitmapToCache(url, bitmap);
            }
            return bitmap;
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            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);
            }
            mTasks.remove(this);
        }
    }
}

新闻适配器

NewsAdapter.java

package io.github.deligencc.asynctask;

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 bummer on 2017/8/22.
 */

public class NewsAdapter extends BaseAdapter implements AbsListView.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) {
        this.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;
            //获得data所有URL 转到静态数组中
        }
        mFirstIn = true;
        //注册事件接口
        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 = mInflater.inflate(R.layout.item_layout,null);
           viewHolder.ivIcon = (ImageView) convertView.findViewById(R.id.iv_icon);
           // new ImageLoader().showImageByThread(viewHolder.ivIcon,mList.get(position).newsIconUrl);
            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.mipmap.ic_launcher);
        String url = mList.get(position).newsIconUrl;
        viewHolder.ivIcon.setTag(url);//作为身份标识
       // new ImageLoader().showImageByThread(viewHolder.ivIcon,mList.get(position).newsIconUrl);
        mImageLoader.loadImages(mStart,mEnd);
        viewHolder.tvTitle.setText(mList.get(position).newsTitle);
        viewHolder.tvContent.setText(mList.get(position).newsContent);
        return convertView;
    }

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {
        //状态改变时会调用
        if(scrollState == SCROLL_STATE_IDLE){
            //加载可见项
            mImageLoader.loadImages(mStart,mEnd);
        }else {
            //停止所有的加载任务
            mImageLoader.cancelAllTasks();
        }
    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
      //整个滑动中都会被调用
        mStart = firstVisibleItem;
        mEnd = firstVisibleItem+visibleItemCount;
        if(mFirstIn && visibleItemCount > 0){
            //当前列表第一次显示， item已经显示出来
            mImageLoader.loadImages(mStart,mEnd);
            mFirstIn = false;
        }
}
 class ViewHolder{
 public TextView tvTitle,tvContent; 
public ImageView ivIcon; 
}

}

新闻实体类

NewsBean.java

package io.github.deligencc.asynctask;

/**
 * Created by bummer on 2017/8/22.
 */

public class NewsBean {
    //图片网址
    public String newsIconUrl;
    public String newsTitle;
    public String newsContent;

}

//布局界面
activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp"
    tools:context="io.github.deligencc.asynctask.MainActivity">

    <ListView
        android:id="@+id/lv_main"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

activity_main.xml布局截图

item_layout.xml

<?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="match_parent"
    android:orientation="horizontal"
    android:padding="4dp">

    <ImageView
        android:id="@+id/iv_icon"
        android:layout_width="64dp"
        android:layout_height="64dp"
        android:gravity="center"
        android:src="@mipmap/ic_launcher" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:paddingLeft="4dp">

        <TextView
            android:id="@+id/tv_title"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:maxLines="1"
            android:text="Title"
            android:textSize="15sp" />

        <TextView
            android:id="@+id/tv_content"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:maxLines="3"
            android:text="Content"
            android:textSize="10sp" />
    </LinearLayout>

</LinearLayout>

item_layout.xml布局截图