【练习】使用接口回调和handler实现数据加载到listview

代码结构

布局：

<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">

    <ListView
        android:id="@+id/listview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
         />
</RelativeLayout>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent" android:layout_height="match_parent">
    <ImageView
        android:id="@+id/img_src"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:scaleType="centerInside"
        android:src="@mipmap/ic_launcher"
        />

    <TextView
        android:id="@+id/tv_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/img_src"
        android:text="见尼日利亚总统布哈里"
        android:textSize="20sp"
        />
    <TextView
        android:id="@+id/tv_digest"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/img_src"
        android:text="称愿支持尼方破解基础设施滞后、人才不足等瓶颈。"
        android:textSize="16sp"
        android:layout_below="@id/tv_title"
        android:layout_marginTop="5dp"
        />
</RelativeLayout>

java代码

public class HttpUtils {
    //下载字符串。
    public static String getJsonString(String path){
        String str = null;
        try {
            URL url = new URL(path);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            //如果不设置网络请求，那么默认就是GET,
            //如果从服务器端拿数据，那么就用get,如果上传数据到服务器端，那么就用post 请求
            conn.setRequestMethod("GET");
            conn.setConnectTimeout(5000);
            conn.setReadTimeout(4000);
            conn.connect();;
            //会得到服务器端返回的响应码。
            int code = conn.getResponseCode();
            //判断响应码。如果成功响应----200
            if(code==200){
                //读取数据。
                InputStream is =  conn.getInputStream();
                //内存流。
                ByteArrayOutputStream bos = new ByteArrayOutputStream();
                byte[] b = new byte[1024*2];
                int length = -1;
                while((length=is.read(b))!=-1){
                    bos.write(b,0,length);
                }
                str = bos.toString();
                is.close();
                return str;
            }
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return str;
    }
    //下载图片。
    public static Bitmap getImageBitmap(String path){
        try {
            URL url = new URL(path);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            int code = connection.getResponseCode();
            if(code==200){
                InputStream is =   connection.getInputStream();
                Bitmap bitmap =  BitmapFactory.decodeStream(is);
                return bitmap;
            }
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }
}

public class JSONUtils {
    public static List<News> parseJsonString(String json) {
        if (json != null) {
            try {
                JSONObject obj = new JSONObject(json);
               JSONArray array =  obj.getJSONArray("T1348647909107");
                List<News> list = JSON.parseArray(array.toString(), News.class);
                return list;
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
        return null;
    }
}

public class NetUtils {
    //创建线程池。
    private  static ExecutorService executor = Executors.newFixedThreadPool(3);
    //处理字符串的接口。
    public interface  LoadStringInterface{
        public void processJsonString(String str);
    }
    // 处理图片的接口
    public interface ImageListener{
        public void processImage(Bitmap bitmap);
    }
    //写一个方法。开启线程去下载字符串。
    public static void startLoadString(final String path, final LoadStringInterface stringListener){
        executor.execute(new Runnable() {
            @Override
            public void run() {
                //下载数据。
              String str =   HttpUtils.getJsonString(path);
                //处理实现接口的类去处理字符串。
                stringListener.processJsonString(str);
            }
        });
    }
    //写一个方法，开启线程去下载图片。
    public static void startLoadImage(final String path,final ImageListener imageListener){
        executor.execute(new Runnable() {
            @Override
            public void run() {
                //下载图片。
               Bitmap bitmap =  HttpUtils.getImageBitmap(path);
                imageListener.processImage(bitmap);
            }
        });
    }
}

public class MainActivity extends AppCompatActivity {
    private ListView listview;
    private NewsAdapter adapter;
    private List<News> list;
    private Handler handler = new Handler();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listview = (ListView) findViewById(R.id.listview);
        list = new ArrayList<News>();
        adapter = new NewsAdapter(list, this, handler);
        listview.setAdapter(adapter);
        //调用方法下载json字符数据。
        NetUtils.startLoadString(Contants.NEWS_URL, new NetUtils.LoadStringInterface() {
            @Override
            public void processJsonString(String str) {
                if (str != null) {
                    Log.i("Main", Thread.currentThread().getName() + "---processJsonString");
                    final List<News> news = JSONUtils.parseJsonString(str);
                    handler.post(new Runnable() {
                        @Override
                        public void run() {
                            adapter.addData(news);
                            Log.i("Main", Thread.currentThread().getName() + "---post--run");
                        }
                    });
                }
            }
        });
    }
}

public class NewsAdapter extends BaseAdapter {
    private List<News> list;
    private Context context;
    private Handler handler;
    public NewsAdapter(List<News> list,Context context,Handler handler){
        this.list = list;
        this.context  = context;
        this.handler = handler;
    }
    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        return list.get(position);
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        final ViewHolder viewHolder;
        if(convertView==null){
            convertView = LayoutInflater.from(context).inflate(R.layout.list_item,parent,false);
            viewHolder = new ViewHolder();
            viewHolder.imgview = (ImageView) convertView.findViewById(R.id.img_src);
            viewHolder.tv_digest = (TextView) convertView.findViewById(R.id.tv_digest);
            viewHolder.tv_title = (TextView) convertView.findViewById(R.id.tv_title);
            convertView.setTag(viewHolder);
        }else{
            viewHolder = (ViewHolder) convertView.getTag();
        }
        News news = list.get(position);
        viewHolder.tv_title.setText(news.getTitle());
        viewHolder.tv_digest.setText(news.getDigest());
        //下载图片。
        String image_path = news.getImgsrc();
        viewHolder.imgview.setTag(image_path);
        //调用方法，开启线程下载数据。
        NetUtils.startLoadImage(image_path, new NetUtils.ImageListener() {
            @Override
            public void processImage(final Bitmap bitmap) {
                Log.i("Main", Thread.currentThread().getName() + "---processImage");

                if(bitmap!=null){
                    handler.post(new Runnable() {
                        @Override
                        public void run() {
                            viewHolder.imgview.setImageBitmap(bitmap);
                            Log.i("Main", Thread.currentThread().getName() + "---post--run-image");
                        }
                    });
                }
            }
        });
        return convertView;
    }
    class ViewHolder{
        ImageView imgview;
        TextView tv_title,tv_digest;
    }
    //添加数据到集合中。
    public void addData(List<News> news){
        list.addAll(news);
        notifyDataSetChanged();
    }
}