使用Handler加载网络图片，设置ListView

加载网络图片生成listview，通过打开网络连接，通过异步线程处理网络加载，并设置图片

MainActivity代码

连接网络，解析JSON代码，将所解析出的Json对象封存，添加到List中并与之后自定义的Adapter关联

public class MainActivity extends AppCompatActivity {
    private List<Newsbeans> mlist;
    private static  String url="http://www.imooc.com/api/teacher?type=4&num=30";
    private ListView listView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Myaysctask myaysctask=new Myaysctask();
        //将url传递进去实现对于url的异步访问
        new Myaysctask().execute(url);
        listView= (ListView) findViewById(R.id.listview);
    }
    //将url转化为我们所需要的json对象
    private List<Newsbeans> getjsondata(String url){
        //初始化list
        mlist=new ArrayList<>();
        JSONObject jsonObject=null;
        Newsbeans newsbeans=new Newsbeans();
        try {
            //获取字节流
            String jsonstring= readStream(new URL(url).openStream());
            //将传入的字节流转化为json对象
            jsonObject=new JSONObject(jsonstring);
            //得到json下的data下的数组
            JSONArray jsonArray=jsonObject.getJSONArray("data");

            for(int i=0;i<jsonArray.length();i++){
                //遍历json数组的到jsonobject的值
                jsonObject=jsonArray.getJSONObject(i);
                newsbeans=new Newsbeans();
                //将jsonobject中的值赋予到已经封装好的值之中
                newsbeans.newscontent=jsonObject.getString("description");
                newsbeans.newspic=jsonObject.getString("picSmall");
                newsbeans.newstitle=jsonObject.getString("name");
                //将newsbeans添加到list之中
                mlist.add(newsbeans);
            }
        } catch (IOException | JSONException e) {
            e.printStackTrace();
        }
        return mlist;
    }
    private String readStream(InputStream is){
        String result="";
        String line="";
        try {
            //将inputstream传入的为字节流，通过inputstreamreader将字节流转换为字符流
            InputStreamReader irs=new InputStreamReader(is,"utf-8");
            //通过bufferedreader将输入流读取出来
            BufferedReader br= new BufferedReader(irs);
            while ((line= br.readLine())!=null){
                result+=line;
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        return result;
    }
    class Myaysctask extends AsyncTask<String,Void,List<Newsbeans>>{

        @Override
        //进行所有的耗时操作但不包括更改UI
        protected List<Newsbeans> doInBackground(String... strings) {
            //将string数组中的0位返回也就是传入url
            return getjsondata(strings[0]);
        }

        @Override
        //加载所需的adapter
        protected void onPostExecute(List<Newsbeans> newsbeans) {
            Myadapter myadapter=new Myadapter(MainActivity.this,newsbeans);
            listView.setAdapter(myadapter);
            super.onPostExecute(newsbeans);
        }
    }
}

使用高效的adapter，关联listview

public class Myadapter extends BaseAdapter {
    private Context context;
    private List<Newsbeans> mlist;
    private LayoutInflater mlayoutinflater;
    public Myadapter(Context context, List<Newsbeans> mlist1){
        mlist=mlist1;
        mlayoutinflater=LayoutInflater.from(context);
    }
    @Override
    public int getCount() {

        return mlist.size();
    }

    @Override
    public Object getItem(int i) {
        return mlist.get(i);
    }

    @Override
    public long getItemId(int i) {
        return i;
    }

    @Override
    public View getView(int i, View convertview, ViewGroup viewGroup) {
        Viewholder viewholder=null;
        if(convertview==null){
            viewholder=new Viewholder();
            //将item的layout文件转化为view，必须是item文件在之后的view中还要找到对应的控件
            convertview=mlayoutinflater.inflate(R.layout.item,null);
            viewholder.contenttext= (TextView)convertview.findViewById(R.id.tv_content);
            viewholder.imageView=(ImageView)convertview.findViewById(R.id.imageview);
            viewholder.titletext=(TextView)convertview.findViewById(R.id.tv_title);
            convertview.setTag(viewholder);
        }
            else {
            viewholder=(Viewholder)convertview.getTag();
        }
            Newsbeans newsbeans=mlist.get(i);
            viewholder.imageView.setImageResource(R.mipmap.ic_launcher);
            //调用方法传递所需信息
            new ImageviewHolder().newthread(viewholder.imageView,mlist.get(i).newspic);
            viewholder.imageView.setTag(mlist.get(i).newspic);
            viewholder.titletext.setText(newsbeans.newstitle);
            viewholder.contenttext.setText(newsbeans.newscontent);
        return convertview;
    }
    class Viewholder{
        public TextView titletext;
        public TextView contenttext;
        public ImageView imageView;
    }
}

使用Handler加载网络图片

public class ImageviewHolder {
    //设置全局变量
    private ImageView mImageView;
    private String mURL;
    //定义handler，在handler之中设定UI
    private android.os.Handler mHadler= new android.os.Handler(){
        @Override
        public void handleMessage(Message msg) {
            //由于Listview的缓存属性，在设加载UI的时候可能会出现重复加载的情况
            if(mImageView.getTag().equals(mURL)){
                mImageView.setImageBitmap((Bitmap) msg.obj);
            }

            super.handleMessage(msg);
        }
    };
    public void newthread(ImageView imageView, final String url){
        mImageView=imageView;
        mURL=url;
        //进行所有的耗时操作
        new Thread(){
            @Override
            public void run(){
                try {
                    Thread.sleep(2000);
                    Message message=new Message();
                    //传递信息，将message的obj设置为一个bitmap并传递给handler设置UI
                    message.obj=getbitmapstream(url);
                    mHadler.sendMessage(message);
                } catch (IOException | InterruptedException e) {
                    e.printStackTrace();
                }
                super.run();
                }
            }.start();
        }
    public Bitmap getbitmapstream(String bitmapurl) throws IOException {
        InputStream is=null;
        try {
            //指向互联网资源的指针
            URL url=new URL(bitmapurl);
            //打开连接，并强行转换格式
            HttpURLConnection connection= (HttpURLConnection) url.openConnection();
            //获取输入的数据流
            is=new BufferedInputStream(connection.getInputStream());
            //解析所传入的数据
            Bitmap bitmap= BitmapFactory.decodeStream(is);
            //断开连接
            connection.disconnect();
            return bitmap;
        } catch (IOException e) {
            e.printStackTrace();
        }
        finally {
            //断开数据流
            assert is != null;
            is.close();
        }
        return null;
    }
    }