Android ListView只載入當前螢幕內的圖片（解決list滑動時載入卡頓）

最近在做ListView分頁顯示，其中包括圖片 和文字（先下載解析文字內容，再非同步載入圖片）發現每次點擊下一頁後，文字內容載入完畢，馬上向下滑動，由於這時後台在用線程池非同步下載圖片，我每頁有20條，也就是20張圖片，會導致listview滑動卡頓！

這是使用者不想看到的，我參考了網易新聞和電子市場等應用，發現它們都是只載入螢幕內的圖片，不現實的不載入,於是我也仿照做了一個。我是菜鳥，我承認 呵呵，雖然不見得完全和他們的一樣，但是確實解決了翻頁時那一刻的卡頓現象。

因為未發現網上有相關文章，希望對朋友們有用~

下面是相關代碼（分頁的就沒放）：

Java代碼

1. /**
2. * list滾動監聽
3. */
4. listView.setOnScrollListener(new OnScrollListener() {
   
5. @Override
6. public void onScrollStateChanged(AbsListView view,
   int scrollState) {
7. // TODO Auto-generated method stub
   
8. // 非同步載入圖片
9. if (scrollState == OnScrollListener.SCROLL_STATE_IDLE) {//list停止滾動時載入圖片
   
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. //設定當前螢幕顯示的起始index和結束index
18. _start_index = firstVisibleItem;
19. _end_index = firstVisibleItem + visibleItemCount;
20. if (_end_index >= totalItemCount) {
    
21. _end_index = totalItemCount - 1;
    
22. }
23. }
24. });

/** * list滾動監聽 */listView.setOnScrollListener(new OnScrollListener() {@Overridepublic void onScrollStateChanged(AbsListView view, int scrollState) {// TODO Auto-generated method stub// 非同步載入圖片if (scrollState == OnScrollListener.SCROLL_STATE_IDLE) {//list停止滾動時載入圖片pageImgLoad(_start_index, _end_index);}}@Overridepublic void onScroll(AbsListView view, int firstVisibleItem,int visibleItemCount, int totalItemCount) {// TODO Auto-generated method stub//設定當前螢幕顯示的起始index和結束index_start_index = firstVisibleItem;_end_index = firstVisibleItem + visibleItemCount;if (_end_index >= totalItemCount) {_end_index = totalItemCount - 1;}}});

Java代碼

1. /**
2. * 只載入from start_index to end_index 的圖片
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. }

/** * 只載入from start_index to end_index 的圖片  * @param start_index * @param end_index */private void pageImgLoad(int start_index, int end_index) {for (; start_index < end_index; start_index++) {HashMap<String, Object> curr_item = adapter.getItem(start_index);if (curr_item.get(Constant.NEWS_ICON_URL) != null&& curr_item.get(Constant.NEWS_ICON) == null) {loadImage(curr_item);}}}

非同步載入圖片代碼，這裡我之前使用的是AsyncTask，但是繼承AsyncTask後不能被執行多次，所以我改用了線程呼叫handler更新UI：

Java代碼

2. /**
3. * 非同步載入圖片
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)) {//軟引用
    
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. // 從本地載入圖片 如果沒網則直接載入本地圖片
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交給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. }

/** * 非同步載入圖片 * @param curr_item */private void loadImage(final HashMap<String, Object> curr_item) {executorService.submit(new Runnable() {public void run() {try {Drawable curr_icon = null;String icon_URL = (String) curr_item.get(Constant.NEWS_ICON_URL);String newsId = (String) curr_item.get(Constant.NEWS_ID);if (imageCache.containsKey(icon_URL)) {//軟引用SoftReference<Drawable> softReference = imageCache.get(icon_URL);curr_icon = softReference.get();System.out.println("CASE USING SoftReference!!!!!!!!!!!!!!!!!!!!");}if (curr_icon == null) {HttpUtils hu = new HttpUtils();FileUtils fu = new FileUtils();if (hu.is_Intent(Home_Activity.this)) {fu.write2LocalFromIS(Home_Activity.this, newsId+ Constant.SAVE_NEWS_ICON_NAME+ Constant.SAVE_IMG_SUFFIX,hu.getISFromURL(icon_URL));}// 從本地載入圖片 如果沒網則直接載入本地圖片curr_icon = fu.readDrawableFromLocal(Home_Activity.this, newsId+ Constant.SAVE_NEWS_ICON_NAME+ Constant.SAVE_IMG_SUFFIX);imageCache.put(icon_URL, new SoftReference<Drawable>(curr_icon));}curr_item.put(Constant.NEWS_ICON, curr_icon);// UI交給handler更新Message msg = _viewHandler.obtainMessage();msg.arg1 = Constant.MSG_LIST_IMG_OK;msg.sendToTarget();} catch (Exception e) {throw new RuntimeException(e);}}});}

Java代碼

1. handler代碼：

handler代碼：

Java代碼

1. Handler _viewHandler = new Handler() {
   

Handler _viewHandler = new Handler() {

Java代碼

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. };

@Overridepublic void handleMessage(Message msg) {switch (msg.arg1) {case Constant.MSG_LIST_IMG_OK:// 更新UIadapter.notifyDataSetChanged();break;}super.handleMessage(msg);}};

上個圖吧：