解析Json并异步加载数据新闻信息(包括新闻图片)

布满荆棘的人生 2022-06-09 01:10 182阅读 0赞

代码运行实例效果

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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

![Center 1][]

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

![Center 2][]

[Center]: /images/20220609/71bf82f02f034591b692168fc2afc282.png
[Center 1]: /images/20220609/6f88565e41fa40dd806c9861542e1ba2.png
[Center 2]: /images/20220609/692a78e796c44709a0bc5b52177dfe85.png