Util

//單例
        private static NetUtil instance;

    //圖片記憶體快取
    private LruCache<String, Bitmap> cache;
    //HashMap<String, Bitmap> m;//無序的
    //LinkedHashMap<String, Bitmap>m;//有序的
    private File saveDir;

    //私有構造方法
    private NetUtil(Context context) {
        int size = (int)(Runtime.getRuntime().freeMemory() * 0.3);
        cache = new LruCache<>(size);
		
        //圖片檔案快取目錄
        saveDir = new File(context.getCacheDir(), "img_cache");
        //不存在,建立
        if(!saveDir.exists()) {
            saveDir.mkdirs();
        }
    }

    //提供方法,獲取物件
    public static NetUtil getInstance(Context context) {
        if(instance == null) {
            instance = new NetUtil(context);
        }
        return instance;
    }

    /*public interface ImageCallbak2 {
        void onStartLoadImage(String url, ImageView imageView);
        void onLoadImageSuccess(String url, Bitmap bitmap, ImageView imageView);
    }

    public void displayBitmap3(final String urlStr, final ImageView imageView) {
        displayBitmap(urlStr, imageView, new ImageCallbak2() {
            @Override
            public void onStartLoadImage(String url, ImageView imageView) {
                imageView.setTag(url);
            }

            @Override
            public void onLoadImageSuccess(String url, Bitmap bitmap, ImageView imageView) {
                if(imageView.getTag().equals(url)) {
                    imageView.setImageBitmap(bitmap);
                } else {
                    Log.i("TEST", "錯亂");
                }
            }
        });
    }

    public void displayBitmap(final String url, final ImageView imageView, final ImageCallbak2 callbak2) {
        callbak2.onStartLoadImage(url, imageView);
        new AsyncTask<String, Void, Bitmap>(){
            @Override
            protected Bitmap doInBackground(String... strings) {
                return getBitmap(strings[0]);
            }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                callbak2.onLoadImageSuccess(url, bitmap, imageView);
            }
        };
    }*/

    //1 定義介面:合同
    public interface ImageCallback {
        void loadImageSuccess(String url, Bitmap bitmap);
    }

    //////////////////介面回撥
    public void getBitmap(final String urlStr, final ImageCallback callback) {
        new AsyncTask<String, Void, Bitmap>(){
            @Override
            protected Bitmap doInBackground(String... strings) {
                return getBitmap(strings[0]);
            }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                callback.loadImageSuccess(urlStr, bitmap);
            }
        }.execute(urlStr);
    }

    //展示圖片,沒有錯亂
    public void displayBitmap2(final String urlStr, final ImageView imageView) {
        //繫結url到imageview
        imageView.setTag(urlStr);
        new AsyncTask<String, Void, Bitmap>(){
            @Override
            protected Bitmap doInBackground(String... strings) {
                return getBitmap(strings[0]);
            }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                if(imageView.getTag().equals(urlStr)) {
                    imageView.setImageBitmap(bitmap);
                }else {
                    Log.i("TEST", "錯亂");
                }
            }
        }.execute(urlStr);
    }

    //請求一張圖片,展示給ImageView
    //非同步任務
    public void displayBitmap(String urlStr, final ImageView imageView) {
        new AsyncTask<String, Void, Bitmap>(){
            @Override
            protected Bitmap doInBackground(String... strings) {
                return getBitmap(strings[0]);
            }

            @Override
            protected void onPostExecute(Bitmap bitmap) {
                imageView.setImageBitmap(bitmap);
            }
        }.execute(urlStr);
    }


    //獲取圖片
    public Bitmap getBitmap(String urlStr) {
        Bitmap result = null;
        //從記憶體中要
        result = cache.get(url2Key(urlStr));
        //記憶體命中
        if(result != null) {
            Log.i("TEST", "記憶體中載入圖片: " + urlStr);
            return result;
        }

        //從磁碟中要
        result = getBitmapForFile(urlStr);
        //檔案命中
        if(result != null) {
            Log.i("TEST", "磁碟中載入圖片: " + urlStr);
            //先存到記憶體快取
            cache.put(url2Key(urlStr), result);
            return result;
        }

        //從網路中請
        Log.i("TEST", "網路中載入圖片: " + urlStr);
        result = getBitmapForNetwork(urlStr);
        //寫檔案
        saveBitmap2File(urlStr, result);
        //存到記憶體快取
        cache.put(url2Key(urlStr), result);

        return result;
    }

    //將url轉換成key
    //url 做key: 太長;如果作為檔名,不允許/ ?
    private String url2Key(String url) {
        //MD5 摘要方法
        //MessageDigest
        return String.valueOf(url.hashCode());
    }

    //將圖片存到檔案
    private void saveBitmap2File(String urlStr, Bitmap bitmap) {
        //格式: png jpeg(jpg)
        //質量: 0 100
        FileOutputStream fos = null;
        try {
            fos = new FileOutputStream(new File(saveDir,url2Key(urlStr)));
            //圖片質量壓縮,   並輸出到輸出流
            bitmap.compress(Bitmap.CompressFormat.JPEG, 100, fos);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }finally {
            if(fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    //從檔案讀取圖片
    private Bitmap getBitmapForFile(String urlStr) {///////
        //解碼檔案為bitmap圖片
        return BitmapFactory.decodeFile(new File(saveDir, url2Key(urlStr)).getAbsolutePath());
    }

    //執行一個網路請求,返回一個Bitmap
    //這一步做:請求圖片
    private Bitmap getBitmapForNetwork(String urlStr) {
        Bitmap result = null;
        try {
            URL url = new URL(urlStr);
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.setConnectTimeout(5000);
            urlConnection.setReadTimeout(5000);
            int responseCode = urlConnection.getResponseCode();
            if(responseCode == 200) {
                result = BitmapFactory.decodeStream(urlConnection.getInputStream());
            }
        } catch (java.io.IOException e) {
            e.printStackTrace();
        }
        return result;
    }

    ///////////////////普通get請求

    public interface Callbak<T>{
        void onSuccess(T t);
    }

    ///執行一個網路請求,通過回撥返回結果
    public void getRequest(final String urlStr, final Class clazz, final Callbak callbak) {
        new AsyncTask<String, Void, Object>(){
            @Override
            protected Object doInBackground(String... strings) {
                return getRequest(urlStr, clazz);
            }

            @Override
            protected void onPostExecute(Object o) {
                callbak.onSuccess(o);
            }
        }.execute(urlStr);
    }


    //執行一個網路請求,返回bean
    public <T> T getRequest(String urlStr, Class clazz) {
        return (T) new Gson().fromJson(getRequest(urlStr), clazz);
    }

    //執行一個網路請求,返回String結果
    public String getRequest(String urlStr) {
        String result = "";
        try {
            URL url = new URL(urlStr);
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.setConnectTimeout(5000);
            urlConnection.setReadTimeout(5000);
            int responseCode = urlConnection.getResponseCode();
            if(responseCode == 200) {
                result = stream2String(urlConnection.getInputStream());
            }
        } catch (java.io.IOException e) {
            e.printStackTrace();
        }
        return result;
    }

    private String stream2String(InputStream is) throws IOException {
        StringBuilder sb = new StringBuilder();

        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        for (String tmp = br.readLine(); tmp != null; tmp = br.readLine()) {
            sb.append(tmp);
        }

        return sb.toString();
    }`在這裡插入程式碼片`
 

Adapter

private Context context;
    private List<Bean.DataBean>mlist;

    public MyBaseAdafter(Context context) {
        this.context = context;
        mlist = new ArrayList<>();
    }
public void setListData(List<Bean.DataBean> list){
        this.mlist = list;
        notifyDataSetChanged();
}
    @Override
    public int getCount() {
        return mlist.size();
    }

    @Override
    public Bean.DataBean 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) {
        final ViewHoder viewHoder;
        if(convertView==null){
            convertView = LayoutInflater.from(context).inflate(R.layout.item,parent,false);
            viewHoder = new ViewHoder();
            viewHoder.textView1 = convertView.findViewById(R.id.textview1);
            viewHoder.textView2 = convertView.findViewById(R.id.textview2);
            viewHoder.imageView = convertView.findViewById(R.id.imageview);
            convertView.setTag(viewHoder);
        }else{
            viewHoder = (ViewHoder) convertView.getTag();
        }
        viewHoder.textView1.setText(mlist.get(position).getNews_title());
        viewHoder.textView2.setText(mlist.get(position).getNews_summary());
       //載入圖片
        //錯亂問題
        //NetUtil.getInstance().displayBitmap(getItem(position).getPic_url(), viewHoder.imageView);

        //NetUtil.getInstance().displayBitmap2(getItem(position).getPic_url(), viewHoder.imageView);


        viewHoder.imageView.setTag(getItem(position).getPic_url());
        NetUtil.getInstance(context).getBitmap(getItem(position).getPic_url(), new NetUtil.ImageCallback() {
            @Override
            public void loadImageSuccess(String url, Bitmap bitmap) {
                if(viewHoder.imageView.getTag().equals(url)) {
                    viewHoder.imageView.setImageBitmap(bitmap);
                }else {

                }
            }
        });

        return convertView;
    }
    class ViewHoder{
        private TextView textView1,textView2;
        private ImageView imageView;
    }