一開始從慕課網學習到的非同步載入顯示圖片，今天終於有時間按照記憶寫了份非同步載入圖片程式碼；有很多小細節需要注意的。
步驟：
   1、先解析完JSon資料，並存放在List中間
   2、非同步下載圖片，放在Item.xml中
   3、listView.setAdapter(teacherAapter);

• 1、從類開始介紹：

  • Teacher：圖片bean
  • TeacherAdapter：介面卡
  • ImageLoad:根據URL獲取圖片，顯示到Item.xml中
  • MainActivity：從Json中獲取資料，呼叫介面卡，並顯示；

• 2、解析Json

  • 通過Thread來適配

public
 
  void getTeacher()
    {
        new Thread()
        {
            @Override
            public void run() {

                try
                {
                    OkHttpClient client = new OkHttpClient();
                    Request request = new Request.Builder()
                            .url("http://www.imooc.com/api/teacher?type=4&num=30"
 
)
                            .build();
                    Response response = client.newCall(request).execute();
                    String data = response.body().string();
                    parseJson(data);
                    //初始化介面卡和列表
                    final TeacherAapter teacherAapter = new
 
 TeacherAapter(MainActivity.this,teacherList);
                    runOnUiThread(new Runnable() {
                        @Override
                        public void run() {
                        //在子執行緒中設定介面 
                            listView.setAdapter(teacherAapter);
                        }
                    });
                }catch (Exception e)
                {
                    e.printStackTrace();
                }
            }
        }.start();
    }
    //解析Json
    public  void parseJson(String data)
    {
        try
        {
            JSONObject jsonObject1 = new JSONObject(data);
            JSONArray jsonArray = jsonObject1.getJSONArray("data");
            System.out.println("length:"+jsonArray.length());
            for(int i=0;i<jsonArray.length();i++)
            {
                JSONObject jsonObject = jsonArray.getJSONObject(i);
                Teacher teacher = new Teacher();
                teacher.setName(jsonObject.getString("name"));
                Log.d("name:",jsonObject.getString("name"));
                teacher.setPicSmall(jsonObject.getString("picSmall"));
                teacher.setDescription(jsonObject.getString("description"));
                teacherList.add(teacher);
                System.out.println("tea_list:"+teacherList.size());
            }
        }catch (Exception e)
        {
            e.printStackTrace();
        }
    }

• AsyncTask 非同步載入來適配

class MyAsyncTask extends AsyncTask<String,Void,List<Teacher>>
    {
        @Override
        protected List<Teacher> doInBackground(String... params) {

            teacherList = getTeacher(params[0]);
            return teacherList;
        }

        @Override
        protected void onPostExecute(List<Teacher> teacherList) {
            super.onPostExecute(teacherList);
            TeacherAapter teacherAapter = new TeacherAapter(MainActivity.this,teacherList);
            listView.setAdapter(teacherAapter);
        }
    }

//呼叫非同步任務
new MyAsyncTask().execute(url);

• 3、載入圖片
  
  • 通過Thread載入

 Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
//            通過判斷載入的路徑是否正確來載入圖片，
            if (imageView.getTag().equals(url))
                imageView.setImageBitmap((Bitmap) msg.obj);
        }
    };
public void showImageByThread(ImageView imageView, final String url) {

        this.url = url;
        this.imageView = imageView;
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Bitmap bitmap = getFromCache(url);
                    if (bitmap == null) {
                        URL url1 = new URL(url);
                        HttpURLConnection connection = (HttpURLConnection) url1.openConnection();
                        InputStream is = connection.getInputStream();
                        bitmap = BitmapFactory.decodeStream(is);
                        is.close();

                        //加入快取
                        addToCache(url, bitmap);
                    }
//                    OkHttpClient client = new OkHttpClient();
//                    Request request = new Request.Builder()
//                            .url(url)
//                            .build();
//                    Response response = client.newCall(request).execute();
//                    byte[] b =response.body().string().getBytes();
//                    System.out.println("b.length"+b.length);
//                    bitmap = BitmapFactory.decodeByteArray(b,0,b.length);
                    Message message = handler.obtainMessage();
                    message.obj = bitmap;
                    handler.sendMessage(message);

                } catch (Exception e) {
                    e.printStackTrace();
                }

            }
        }).start();
    }

• 通過非同步載入圖片

//通過非同步的方法載入
    public void showImageByAsy(ImageView imageView, final String url) {
        this.url = url;
        this.imageView = imageView;
        new MyAsyLoad().execute(url);
    }


    class MyAsyLoad extends AsyncTask<String, Void, Bitmap> {
        @Override
        protected Bitmap doInBackground(String... params) {
            Bitmap bitmap = getFromCache(params[0]);
            if (bitmap != null)
                return bitmap;
            try {
                URL url1 = new URL(params[0]);
                HttpURLConnection connection = (HttpURLConnection) url1.openConnection();
                InputStream is = connection.getInputStream();
                bitmap = BitmapFactory.decodeStream(is);
                is.close();
                addToCache(params[0], bitmap);
            } catch (Exception e) {
                e.printStackTrace();
            }
            return bitmap;
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            if (bitmap != null && imageView != null)
                imageView.setImageBitmap(bitmap);
        }
    }

• 4、Lrucache快取

private LruCache<String, Bitmap> mCache;

    public ImageLoad() {
        int maxMemory = (int) Runtime.getRuntime().maxMemory();
        int cacheSize = maxMemory / 8;
        // 設定圖片快取大小為程式最大可用記憶體的1/8
        mCache = new LruCache<String, Bitmap>(cacheSize) {
            @Override
            protected int sizeOf(String key, Bitmap bitmap) {
                return bitmap.getByteCount();
            }
        };
    }