Android ListView只加载当前屏幕内的图片（解决list滑动时加载卡顿）

最近在做ListView分页显示，其中包括图片 和文字（先下载解析文字内容，再异步加载图片）发现每次点击下一页后，文字内容加载完毕，马上向下滑动，由于这时后台在用线程池异步下载图片，我每页有20条，也就是20张图片，会导致listview滑动卡顿！

这是用户不想看到的，我参考了网易新闻和电子市场等应用，发现它们都是只加载屏幕内的图片，不现实的不加载,于是我也仿照做了一个。我是菜鸟，我承认 呵呵，虽然不见得完全和他们的一样，但是确实解决了翻页时那一刻的卡顿现象。

因为未发现网上有相关文章，希望对朋友们有用~

下面是相关代码（分页的就没放）：

Java代码  

1. /**

2. * list滚动监听

3. */

4. listView.setOnScrollListener(new OnScrollListener() {

5. @Override

6. public void onScrollStateChanged(AbsListView view, int scrollState) {

7. // TODO Auto-generated method stub

8. // 异步加载图片

9. if (scrollState == OnScrollListener.SCROLL_STATE_IDLE) {//list停止滚动时加载图片

10. pageImgLoad(_start_index, _end_index);

11. }

12. }

13. @Override

14. public void onScroll(AbsListView view, int firstVisibleItem,

15. int visibleItemCount, int totalItemCount) {

16. // TODO Auto-generated method stub

17. //设置当前屏幕显示的起始index和结束index

18. _start_index = firstVisibleItem;

19. _end_index = firstVisibleItem + visibleItemCount;

20. if (_end_index >= totalItemCount) {

21. _end_index = totalItemCount - 1;

22. }

23. }

24. });

[java] view plain copy

1. /** 

2.      * list滚动监听 

3.      */  

4.     listView.setOnScrollListener(new OnScrollListener() {  

5.         @Override  

6.         public void onScrollStateChanged(AbsListView view, int scrollState) {  

7.             // TODO Auto-generated method stub  

8.             // 异步加载图片  

9.             if (scrollState == OnScrollListener.SCROLL_STATE_IDLE) {//list停止滚动时加载图片  

10.                 pageImgLoad(_start_index, _end_index);  

11.             }  

12.         }  

13.         @Override  

14.         public void onScroll(AbsListView view, int firstVisibleItem,  

15.                 int visibleItemCount, int totalItemCount) {  

16.             // TODO Auto-generated method stub  

17.             //设置当前屏幕显示的起始index和结束index  

18.             _start_index = firstVisibleItem;  

19.             _end_index = firstVisibleItem + visibleItemCount;  

20.             if (_end_index >= totalItemCount) {  

21.                 _end_index = totalItemCount - 1;  

22.             }  

23.         }  

24.     });  

Java代码  

1. /**

2. * 只加载from start_index to end_index 的图片

3. * @param start_index

4. * @param end_index

5. */

6. private void pageImgLoad(int start_index, int end_index) {

7. for (; start_index < end_index; start_index++) {

8. HashMap<String, Object> curr_item = adapter.getItem(start_index);

9. if (curr_item.get(Constant.NEWS_ICON_URL) != null

10. && curr_item.get(Constant.NEWS_ICON) == null) {

11. loadImage(curr_item);

12. }

13. }

14. }

[java] view plain copy

1. /** 

2.      * 只加载from start_index to end_index 的图片  

3.      * @param start_index 

4.      * @param end_index 

5.      */  

6.     private void pageImgLoad(int start_index, int end_index) {  

7.         for (; start_index < end_index; start_index++) {  

8.             HashMap<String, Object> curr_item = adapter.getItem(start_index);  

9.             if (curr_item.get(Constant.NEWS_ICON_URL) != null  

10.                     && curr_item.get(Constant.NEWS_ICON) == null) {  

11.                 loadImage(curr_item);  

12.             }  

13.         }  

14.     }  

异步加载图片代码，这里我之前使用的是AsyncTask，但是继承AsyncTask后不能被执行多次，所以我改用了线程呼叫handler更新UI：

Java代码  

2. /**

3. * 异步加载图片

4. * @param curr_item

5. */

6. private void loadImage(final HashMap<String, Object> curr_item) {

7. executorService.submit(new Runnable() {

8. public void run() {

9. try {

10. Drawable curr_icon = null;

11. String icon_URL = (String) curr_item

12. .get(Constant.NEWS_ICON_URL);

13. String newsId = (String) curr_item.get(Constant.NEWS_ID);

15. if (imageCache.containsKey(icon_URL)) {//软引用

16. SoftReference<Drawable> softReference = imageCache

17. .get(icon_URL);

18. curr_icon = softReference.get();

19. System.out.println("CASE USING SoftReference!!!!!!!!!!!!!!!!!!!!");

20. }

21. if (curr_icon == null) {

22. HttpUtils hu = new HttpUtils();

23. FileUtils fu = new FileUtils();

24. if (hu.is_Intent(Home_Activity.this)) {

25. fu.write2LocalFromIS(Home_Activity.this, newsId

26. + Constant.SAVE_NEWS_ICON_NAME

27. + Constant.SAVE_IMG_SUFFIX,

28. hu.getISFromURL(icon_URL));

29. }

30. // 从本地加载图片 如果没网则直接加载本地图片

31. curr_icon = fu.readDrawableFromLocal(

32. Home_Activity.this, newsId

33. + Constant.SAVE_NEWS_ICON_NAME

34. + Constant.SAVE_IMG_SUFFIX);

35. imageCache.put(icon_URL, new SoftReference<Drawable>(

36. curr_icon));

37. }

38. curr_item.put(Constant.NEWS_ICON, curr_icon);

39. // UI交给handler更新

40. Message msg = _viewHandler.obtainMessage();

41. msg.arg1 = Constant.MSG_LIST_IMG_OK;

42. msg.sendToTarget();

43. } catch (Exception e) {

44. throw new RuntimeException(e);

45. }

46. }

47. });

48. }

[java] view plain copy

1. /** 

2.      * 异步加载图片 

3.      * @param curr_item 

4.      */  

5.     private void loadImage(final HashMap<String, Object> curr_item) {  

6.         executorService.submit(new Runnable() {  

7.             public void run() {  

8.                 try {  

9.                     Drawable curr_icon = null;  

10.                     String icon_URL = (String) curr_item  

11.                             .get(Constant.NEWS_ICON_URL);  

12.                     String newsId = (String) curr_item.get(Constant.NEWS_ID);  

13.   

14.                     if (imageCache.containsKey(icon_URL)) {//软引用  

15.                         SoftReference<Drawable> softReference = imageCache  

16.                                 .get(icon_URL);  

17.                         curr_icon = softReference.get();  

18.                         System.out.println("CASE USING SoftReference!!!!!!!!!!!!!!!!!!!!");  

19.                     }  

20.                     if (curr_icon == null) {  

21.                         HttpUtils hu = new HttpUtils();  

22.                         FileUtils fu = new FileUtils();  

23.                         if (hu.is_Intent(Home_Activity.this)) {  

24.                             fu.write2LocalFromIS(Home_Activity.this, newsId  

25.                                     + Constant.SAVE_NEWS_ICON_NAME  

26.                                     + Constant.SAVE_IMG_SUFFIX,  

27.                                     hu.getISFromURL(icon_URL));  

28.                         }  

29.                         // 从本地加载图片 如果没网则直接加载本地图片  

30.                         curr_icon = fu.readDrawableFromLocal(  

31.                                 Home_Activity.this, newsId  

32.                                         + Constant.SAVE_NEWS_ICON_NAME  

33.                                         + Constant.SAVE_IMG_SUFFIX);  

34.                         imageCache.put(icon_URL, new SoftReference<Drawable>(  

35.                                 curr_icon));  

36.                     }  

37.                     curr_item.put(Constant.NEWS_ICON, curr_icon);  

38.                     // UI交给handler更新  

39.                     Message msg = _viewHandler.obtainMessage();  

40.                     msg.arg1 = Constant.MSG_LIST_IMG_OK;  

41.                     msg.sendToTarget();  

42.                 } catch (Exception e) {  

43.                     throw new RuntimeException(e);  

44.                 }  

45.             }  

46.         });  

47.     }  

Java代码  

1. handler代码：

[java] view plain copy

1. handler代码：  

Java代码  

1. Handler _viewHandler = new Handler() {

[java] view plain copy

1. Handler _viewHandler = new Handler() {  

Java代码  

1. @Override

2. public void handleMessage(Message msg) {

3. switch (msg.arg1) {

4. case Constant.MSG_LIST_IMG_OK:

5. // 更新UI

6. adapter.notifyDataSetChanged();

7. break;

8. }

9. super.handleMessage(msg);

10. }

11. };

[java] view plain copy

1. @Override  

2.     public void handleMessage(Message msg) {  

3.         switch (msg.arg1) {  

4.         case Constant.MSG_LIST_IMG_OK:  

5.             // 更新UI  

6.             adapter.notifyDataSetChanged();  

7.             break;  

8.         }  

9.         super.handleMessage(msg);  

10.     }  

11. };  

原文链接：http://www.apkbus.com/blog-843025-62036.html