Android：异步加载网络资源

网络资源

慕课网提供了获取课程信息的地址：http://www.imooc.com/api/teacher?type=4&num=30，可以获取json格式表述的30门课程的图标、标题、描述、学员数等信息。

{
    "status": 1,
    "data": [
        {
            "id": 1,
            "name": "Tony老师聊shell——环境变量配置文件",
            "picSmall": "http://img.mukewang.com/55237dcc0001128c06000338-300-170.jpg",
            "picBig": "http://img.mukewang.com/55237dcc0001128c06000338.jpg",
            "description": "为你带来shell中的环境变量配置文件",
            "learner": 12312
        },
        {
            "id": 2,
            "name": "数学知识在CSS动画中的应用",
            "picSmall": "http://img.mukewang.com/55249cf30001ae8a06000338-300-170.jpg",
            "picBig": "http://img.mukewang.com/55249cf30001ae8a06000338.jpg",
            "description": "数学知识与CSS结合实现酷炫效果",
            "learner": 45625
        },
		......
    ],
    "msg": "成功"
}

---

实现效果

异步获取课程信息，并用ListView列表展示。

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实现代码

activity_load_news.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="5dp">

    <ListView
        android:id="@+id/lv_news"
        android:layout_width="match_parent"
        android:layout_height="match_parent"></ListView>
</LinearLayout>

news_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="5dp">

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

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:paddingLeft="10dp"
        android:layout_gravity="center">

        <TextView
            android:id="@+id/tv_news_title"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Title"
            android:maxLines="1"
            android:textSize="16sp"
            android:textColor="@color/black"/>

        <TextView
            android:id="@+id/tv_news_content"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Content"
            android:maxLines="3"
            android:textSize="12sp"
            android:textColor="@color/steelblue"/>
    </LinearLayout>
</LinearLayout>

LoadNewsActivity.java

public class LoadNewsActivity extends Activity {

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

    private ListView lv_news;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_load_news);

        lv_news = (ListView) findViewById(R.id.lv_news);

        new LoadNewsAsyncTask(this, lv_news).execute(URL);
    }
}

LoadNewsAsyncTask.java

/**
 * 异步加载网络资源
 */
public class LoadNewsAsyncTask extends AsyncTask<String, Void, List<NewsBean>> {

    private Context ctx;
    private ListView lv_news;

    public LoadNewsAsyncTask(Context context, ListView lv) {
        ctx = context;
        lv_news = lv;
    }

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

    @Override
    protected void onPostExecute(List<NewsBean> newsBeans) {
        super.onPostExecute(newsBeans);

        NewsAdapter adapter = new NewsAdapter(ctx, newsBeans);
        lv_news.setAdapter(adapter);
    }

    /**
     * 通过url读取json
     * @param url
     * @return
     */
    private List<NewsBean> getJsonData(String url) {
        List<NewsBean> newsBeanList = new ArrayList<>();

        try {
            String jsonString = readStream(new URL(url).openStream());

            JSONObject jsonObject = new JSONObject(jsonString);

            if (jsonObject != null) {
                JSONArray jsonArray = jsonObject.getJSONArray("data");
                if (jsonArray != null) {
                    int count = jsonArray.length();
                    for (int i = 0; i < count; i++) {
                        JSONObject obj = jsonArray.getJSONObject(i);
                        if (obj != null) {
                            NewsBean bean = new NewsBean();
                            bean.IconUrl = obj.getString("picSmall");
                            bean.Title = obj.getString("name");
                            bean.Content = obj.getString("description");
                            newsBeanList.add(bean);
                        }
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }

        return newsBeanList;
    }

    /**
     * 读取inputstream中的文本
     * @param is
     * @return
     */
    private String readStream(InputStream is) {
        InputStreamReader isr;
        String result = "";

        try {
            String line = "";
            isr = new InputStreamReader(is, "utf-8");
            BufferedReader br = new BufferedReader(isr);
            while ((line = br.readLine()) != null) {
                result += line;
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return result;
    }
}

NewsBean.java

/**
 * 封装json数据
 */
public class NewsBean {
    /**
     * 图标地址
     */
    public String IconUrl = "";
    /**
     * 标题
     */
    public String Title = "";
    /**
     * 内容
     */
    public String Content = "";
}

NewsAdapter.java

public class NewsAdapter extends BaseAdapter {

    private LayoutInflater inflater;
    private List<NewsBean> list;

    public NewsAdapter(Context context, List<NewsBean> newsBeanList) {
        inflater = LayoutInflater.from(context);
        list = newsBeanList;
    }

    @Override
    public int getCount() {
        return list.size();
    }

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

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

    @Override
    public View getView(int i, View view, ViewGroup viewGroup) {

        if (view == null) {
            view = inflater.inflate(R.layout.news_item, null);

            NewsBean bean = list.get(i);

            ImageView imageView = (ImageView) view.findViewById(R.id.iv_news);
            ImageLoader imageLoader = new ImageLoader(imageView, bean.IconUrl);
//            imageLoader.showImageByThread();//异步加载图片
            imageLoader.showImageByAsyncTask();

            TextView txtTitle = (TextView) view.findViewById(R.id.tv_news_title);
            txtTitle.setText(bean.Title);

            TextView txtContent = (TextView) view.findViewById(R.id.tv_news_content);
            txtContent.setText(bean.Content);
        }
        return view;
    }
}

ImageLoader.java

/**
 * 异步加载网络图片
 */
public class ImageLoader {

    private ImageView iv;
    private String urlAddress;

    public ImageLoader(ImageView imageView, String url) {
        iv = imageView;
        urlAddress = url;
    }

	//region 多线程

    /**
     * 接收异步线程的消息，更新主线程的ui
     */
    private Handler handler = new Handler() {

        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            iv.setImageBitmap((Bitmap) msg.obj);
        }
    };

    /**
     * 使用多线程异步加载图片
     * 异步线程不能直接更新ui，需要利用Message
     */
    public void showImageByThread() {
        new Thread(){

            @Override
            public void run() {
                super.run();

                //获取网络图片
                Bitmap bitmap = getBitmapFromURL(urlAddress);

                //通知主线程更新图片
                Message message = Message.obtain();//获取现有的以及回收的message，提高message的使用效率
                message.obj = bitmap;
                handler.sendMessage(message);
            }
        }.start();
    }

	//endregion

	//region AsyncTask方式

    /**
     * AsyncTask是在多线程的基础上进行了封装，可利用onPostExecute方法直接更新ui
     */
    public void showImageByAsyncTask() {
        new LoadImageAsyncTask().execute(urlAddress);
    }

    class LoadImageAsyncTask extends AsyncTask<String, Void, Bitmap> {

        @Override
        protected Bitmap doInBackground(String... strings) {
            return getBitmapFromURL(strings[0]);
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            super.onPostExecute(bitmap);

            iv.setImageBitmap(bitmap);
        }
    }

	//endregion

    /**
     * 加载网络图片
     * @param urlString
     * @return
     */
    private Bitmap getBitmapFromURL(String urlString) {
        Bitmap bitmap = null;
        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();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                is.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return bitmap;
    }
}

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参考：http://www.imooc.com/learn/406