Android----异步加载

MainActivity.java

public class MainActivity extends Activity{
    private ListView mListView;
    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.main);
       mListView=(ListView)findViewById(R.id.lv_main);
       new NewAsyncTask().execute(URL);
    }
    class NewAsyncTask extends AsyncTask<String,Void,List<NewsBean>>{

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

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

    private List<NewsBean> getJsonData(String param) {
        List<NewsBean> newsBeanList=new ArrayList<>();
        try {
            String jsonString=readStream(new URL(param).openStream());
            JSONObject jsonObject;
            NewsBean newsBean;
            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);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return newsBeanList;
    }
    private String readStream(InputStream is){//字节流
        InputStreamReader isr;
        String result="";
        try {
            String line="";
            isr=new InputStreamReader(is,"utf-8");//将字节流转化为字符流
            BufferedReader br=new BufferedReader(isr);//封装buffer
                    while((line=br.readLine())!=null){
                        result+=line;
                    }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }

}

NewsAdapter.java

public class NewsAdapter extends BaseAdapter {
    private List<NewsBean> mList;
    private LayoutInflater mInflater;

    public NewsAdapter(Context context,List<NewsBean> data) {
        mList = data;
        mInflater=LayoutInflater.from(context);
    }

    @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.main1,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.mipmap.ic_launcher);
        String url=mList.get(position).newsIconUrl;
        viewHolder.ivIcon.setTag(url);
        new ImageLoader().showImageByThread(viewHolder.ivIcon,url);
        viewHolder.tvTitle.setText(mList.get(position).newsTitle);
        viewHolder.tvContent.setText(mList.get(position).newsContent);
        return convertView;
    }
    class ViewHolder{
        public TextView tvTitle,tvContent;
        public ImageView ivIcon;
    }
}

ImageLoader.java

public class ImageLoader {
    private ImageView mimageView;
    private String murl;
    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(){
             @Override
             public void run() {
                 super.run();
                 Bitmap bitmap=getBitmapFromURL(url);
                 Message message=Message.obtain();
                 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();
            return bitmap;
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return null;
    }
}

NewsBean.java

public class NewsBean {
    public String newsIconUrl;
    public String newsTitle;
    public String newsContent;
}

main1.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="wrap_content"
    android:orientation="horizontal">
    <ImageView
        android:id="@+id/iv_icon"
        android:layout_width="94dp"
        android:layout_height="94dp"
        android:src="@mipmap/ic_launcher"/>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        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>

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"
    android:gravity="center_horizontal"
    android:orientation="vertical"
    android:paddingLeft="10dp"
    android:paddingRight="10dp">
    <ListView
        android:id="@+id/lv_main"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </ListView>
   </RelativeLayout>