http://www.iteye.com/topic/1118828

http://www.iteye.com/topic/1127914

这样做无疑是非常可取的方法，但是加载图片时仍然会感觉到轻微的卡屏现象，特别是listview里的item在进行快速滑动的时候。

如果在同一时间调用handler刷新UI次数多了就会造成这样的卡屏现象。

我们只需要在listview滑动停止之后再去加载listview里面显示的几个item里面的图片就好了。

1.在adapter 的 getview方法里面启动加载图片的thread，如果listview在滑动则wait

    public View getView(int position, View convertView, ViewGroup parent) {

        if(convertView == null){

            convertView = mInflater.inflate(R.layout.book_item_adapter, null);

        }

        BookModel model = mModels.get(position);

        convertView.setTag(position);

        ImageView iv = (ImageView) convertView.findViewById(R.id.sItemIcon);

        TextView sItemTitle =  (TextView) convertView.findViewById(R.id.sItemTitle);

        TextView sItemInfo =  (TextView) convertView.findViewById(R.id.sItemInfo);

        sItemTitle.setText(model.book_name);

        sItemInfo.setText(model.out_book_url);

        iv.setBackgroundResource(R.drawable.rc_item_bg);

        syncImageLoader.loadImage(position,model.out_book_pic,imageLoadListener);

        return  convertView;

    }  

    SyncImageLoader.OnImageLoadListener imageLoadListener = new SyncImageLoader.OnImageLoadListener(){  

        @Override

        public void onImageLoad(Integer t, Drawable drawable) {

            //BookModel model = (BookModel) getItem(t);

            View view = mListView.findViewWithTag(t);

            if(view != null){

                ImageView iv = (ImageView) view.findViewById(R.id.sItemIcon);

                iv.setBackgroundDrawable(drawable);

            }

        }

        @Override

        public void onError(Integer t) {

            BookModel model = (BookModel) getItem(t);

            View view = mListView.findViewWithTag(model);

            if(view != null){

                ImageView iv = (ImageView) view.findViewById(R.id.sItemIcon);

                iv.setBackgroundResource(R.drawable.rc_item_bg);

            }

        }  

    };  

    public void loadImage(){

        int start = mListView.getFirstVisiblePosition();

        int end =mListView.getLastVisiblePosition();

        if(end >= getCount()){

            end = getCount() -1;

        }

        syncImageLoader.setLoadLimit(start, end);

        syncImageLoader.unlock();

    }  

    AbsListView.OnScrollListener onScrollListener = new AbsListView.OnScrollListener() {  

        @Override

        public void onScrollStateChanged(AbsListView view, int scrollState) {

            switch (scrollState) {

                case AbsListView.OnScrollListener.SCROLL_STATE_FLING:

                    DebugUtil.debug("SCROLL_STATE_FLING");

                    syncImageLoader.lock();

                    break;

                case AbsListView.OnScrollListener.SCROLL_STATE_IDLE:

                    DebugUtil.debug("SCROLL_STATE_IDLE");

                    loadImage();

                    //loadImage();

                    break;

                case AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:

                    syncImageLoader.lock();

                    break;  

                default:

                    break;

            }  

        }  

        @Override

        public void onScroll(AbsListView view, int firstVisibleItem,

                int visibleItemCount, int totalItemCount) {

            // TODO Auto-generated method stub  

        }

    };

package cindy.android.test.synclistview;

Syncimageloader代码

  1. import java.io.DataInputStream;
  2. import java.io.File;
  3. import java.io.FileInputStream;
  4. import java.io.FileOutputStream;
  5. import java.io.IOException;
  6. import java.io.InputStream;
  7. import java.lang.ref.SoftReference;
  8. import java.net.URL;
  9. import java.util.HashMap;
  10. import android.graphics.drawable.Drawable;
  11. import android.os.Environment;
  12. import android.os.Handler;
  13. public class SyncImageLoader {
  14. private Object lock = new Object();
  15. private boolean mAllowLoad = true;
  16. private boolean firstLoad = true;
  17. private int mStartLoadLimit = 0;
  18. private int mStopLoadLimit = 0;
  19. final Handler handler = new Handler();
  20. private HashMap<String, SoftReference<Drawable>> imageCache = new HashMap<String, SoftReference<Drawable>>();
  21. public interface OnImageLoadListener {
  22. public void onImageLoad(Integer t, Drawable drawable);
  23. public void onError(Integer t);
  24. }
  25. public void setLoadLimit(int startLoadLimit,int stopLoadLimit){
  26. if(startLoadLimit > stopLoadLimit){
  27. return;
  28. }
  29. mStartLoadLimit = startLoadLimit;
  30. mStopLoadLimit = stopLoadLimit;
  31. }
  32. public void restore(){
  33. mAllowLoad = true;
  34. firstLoad = true;
  35. }
  36. public void lock(){
  37. mAllowLoad = false;
  38. firstLoad = false;
  39. }
  40. public void unlock(){
  41. mAllowLoad = true;
  42. synchronized (lock) {
  43. lock.notifyAll();
  44. }
  45. }
  46. public void loadImage(Integer t, String imageUrl,
  47. OnImageLoadListener listener) {
  48. final OnImageLoadListener mListener = listener;
  49. final String mImageUrl = imageUrl;
  50. final Integer mt = t;
  51. new Thread(new Runnable() {
  52. @Override
  53. public void run() {
  54. if(!mAllowLoad){
  55. DebugUtil.debug("prepare to load");
  56. synchronized (lock) {
  57. try {
  58. lock.wait();
  59. } catch (InterruptedException e) {
  60. // TODO Auto-generated catch block
  61. e.printStackTrace();
  62. }
  63. }
  64. }
  65. if(mAllowLoad && firstLoad){
  66. loadImage(mImageUrl, mt, mListener);
  67. }
  68. if(mAllowLoad && mt <= mStopLoadLimit && mt >= mStartLoadLimit){
  69. loadImage(mImageUrl, mt, mListener);
  70. }
  71. }
  72. }).start();
  73. }
  74. private void loadImage(final String mImageUrl,final Integer mt,final OnImageLoadListener mListener){
  75. if (imageCache.containsKey(mImageUrl)) {
  76. SoftReference<Drawable> softReference = imageCache.get(mImageUrl);
  77. final Drawable d = softReference.get();
  78. if (d != null) {
  79. handler.post(new Runnable() {
  80. @Override
  81. public void run() {
  82. if(mAllowLoad){
  83. mListener.onImageLoad(mt, d);
  84. }
  85. }
  86. });
  87. return;
  88. }
  89. }
  90. try {
  91. final Drawable d = loadImageFromUrl(mImageUrl);
  92. if(d != null){
  93. imageCache.put(mImageUrl, new SoftReference<Drawable>(d));
  94. }
  95. handler.post(new Runnable() {
  96. @Override
  97. public void run() {
  98. if(mAllowLoad){
  99. mListener.onImageLoad(mt, d);
  100. }
  101. }
  102. });
  103. } catch (IOException e) {
  104. handler.post(new Runnable() {
  105. @Override
  106. public void run() {
  107. mListener.onError(mt);
  108. }
  109. });
  110. e.printStackTrace();
  111. }
  112. }
  113. public static Drawable loadImageFromUrl(String url) throws IOException {
  114. DebugUtil.debug(url);
  115. if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
  116. File f = new File(Environment.getExternalStorageDirectory()+"/TestSyncListView/"+MD5.getMD5(url));
  117. if(f.exists()){
  118. FileInputStream fis = new FileInputStream(f);
  119. Drawable d = Drawable.createFromStream(fis, "src");
  120. return d;
  121. }
  122. URL m = new URL(url);
  123. InputStream i = (InputStream) m.getContent();
  124. DataInputStream in = new DataInputStream(i);
  125. FileOutputStream out = new FileOutputStream(f);
  126. byte[] buffer = new byte[1024];
  127. int   byteread=0;
  128. while ((byteread = in.read(buffer)) != -1) {
  129. out.write(buffer, 0, byteread);
  130. }
  131. in.close();
  132. out.close();
  133. Drawable d = Drawable.createFromStream(i, "src");
  134. return loadImageFromUrl(url);
  135. }else{
  136. URL m = new URL(url);
  137. InputStream i = (InputStream) m.getContent();
  138. Drawable d = Drawable.createFromStream(i, "src");
  139. return d;
  140. }
  141. }
  142. }

TestSyncListView.rar (147.8
KB)

其实改动不大，就是把之前的new Thread改成了 Handler Looper Thread的模式，这样在第一次滑动的时候就进入了wait状态，又因为handler里面的runnable是队列执行的，所以handler一直在添加的runnable也在等待，这样就避免了多次new
thread的问题，从头到尾就只有一个thread，别的不多说，看修改后的代码。
Runinotherthread代码

    import android.os.Handler;

    import android.os.Looper;

    import android.os.Message;  

    public class RunInOtherThread {

        private static final String LOG_TAG = "RunInOtherThread";  

        private LooperThread localThread = new LooperThread();  

        private boolean isRunning = true;  

        public Handler getHandler(){

            return localThread.getHandler();

        }  

        private class LooperThread extends Thread {

            private Handler mHandler;  

            public void run() {

                Looper.prepare();

                mHandler = new Handler() {

                    public void handleMessage(Message msg) {

                        onReceiveMessage(msg.what);

                    }

                };

                Looper.loop();

            }  

            Handler getHandler(){

                return mHandler;

            }  

        }  

        public void start(){

            localThread.start();

        }  

        public void quit(){

            localThread.getHandler().getLooper().quit();

        }  

        public void sendMessage(int what){

            getHandler().sendEmptyMessage(what);

        }  

        public Thread getThread(){

            return localThread;

        }  

        public void onReceiveMessage(int what){};  

    }  

 Syncimageloader代码

    import java.io.DataInputStream;

    import java.io.File;

    import java.io.FileInputStream;

    import java.io.FileOutputStream;

    import java.io.IOException;

    import java.io.InputStream;

    import java.lang.ref.SoftReference;

    import java.net.URL;

    import java.util.HashMap;  

    import cindy.android.debug.DebugUtil;  

    import android.graphics.drawable.Drawable;

    import android.os.Environment;

    import android.os.Handler;  

    public class SyncImageLoader {  

        private Object lock = new Object();  

        private boolean mAllowLoad = true;  

        private boolean firstLoad = true;  

        private int mStartLoadLimit = 0;  

        private int mStopLoadLimit = 0;  

        final Handler handler = new Handler();  

        private HashMap<String, SoftReference<Drawable>> imageCache = new HashMap<String, SoftReference<Drawable>>();  

        RunInOtherThread runInOutherThread;  

        public SyncImageLoader() {

            super();

            runInOutherThread = new RunInOtherThread();

            runInOutherThread.start();

        }  

        public interface OnImageLoadListener {

            public void onImageLoad(Integer t, Drawable drawable);  

            public void onError(Integer t);

        }  

        public void setLoadLimit(int startLoadLimit, int stopLoadLimit) {

            if (startLoadLimit > stopLoadLimit) {

                return;

            }

            mStartLoadLimit = startLoadLimit;

            mStopLoadLimit = stopLoadLimit;

        }  

        public void restore() {

            mAllowLoad = true;

            firstLoad = true;

        }  

        public void lock() {

            mAllowLoad = false;

            firstLoad = false;

        }  

        public void unlock() {

            mAllowLoad = true;

            synchronized (lock) {

                lock.notifyAll();

            }

        }  

        public void loadImage(Integer t, String imageUrl,

                OnImageLoadListener listener) {

            final OnImageLoadListener mListener = listener;

            final String mImageUrl = imageUrl;

            final Integer mt = t;  

            runInOutherThread.getHandler().post(new Runnable() {  

                @Override

                public void run() {

                    if (!mAllowLoad) {

                        synchronized (lock) {

                            try {

                                DebugUtil.debug("wait start.....");

                                lock.wait();

                                DebugUtil.debug("wait end.....");

                            } catch (InterruptedException e) {

                                // TODO Auto-generated catch block

                                e.printStackTrace();

                            }

                        }

                    }  

                    if (mAllowLoad && firstLoad) {

                        loadImage(mImageUrl, mt, mListener);

                    }  

                    if (mAllowLoad && mt <= mStopLoadLimit && mt >= mStartLoadLimit) {

                        loadImage(mImageUrl, mt, mListener);

                    }

                }  

            });

        }  

        private void loadImage(final String mImageUrl, final Integer mt,

                final OnImageLoadListener mListener) {  

            if (imageCache.containsKey(mImageUrl)) {

                SoftReference<Drawable> softReference = imageCache.get(mImageUrl);

                final Drawable d = softReference.get();

                if (d != null) {

                    handler.post(new Runnable() {

                        @Override

                        public void run() {

                            if (mAllowLoad) {

                                mListener.onImageLoad(mt, d);

                            }

                        }

                    });

                    return;

                }

            }

            try {

                final Drawable d = loadImageFromUrl(mImageUrl);

                if (d != null) {

                    imageCache.put(mImageUrl, new SoftReference<Drawable>(d));

                }

                handler.post(new Runnable() {

                    @Override

                    public void run() {

                        if (mAllowLoad) {

                            mListener.onImageLoad(mt, d);

                        }

                    }

                });

            } catch (IOException e) {

                handler.post(new Runnable() {

                    @Override

                    public void run() {

                        mListener.onError(mt);

                    }

                });

                e.printStackTrace();

            }

        }  

        public static Drawable loadImageFromUrl(String url) throws IOException {

            //DebugUtil.debug(url);

            if (Environment.getExternalStorageState().equals(

                    Environment.MEDIA_MOUNTED)) {

                File f = new File(Environment.getExternalStorageDirectory()

                        + "/TestSyncListView/" + MD5.getMD5(url));

                if (f.exists()) {

                    FileInputStream fis = new FileInputStream(f);

                    Drawable d = Drawable.createFromStream(fis, "src");

                    return d;

                }

                URL m = new URL(url);

                InputStream i = (InputStream) m.getContent();

                DataInputStream in = new DataInputStream(i);

                FileOutputStream out = new FileOutputStream(f);

                byte[] buffer = new byte[1024];

                int byteread = 0;

                while ((byteread = in.read(buffer)) != -1) {

                    out.write(buffer, 0, byteread);

                }

                in.close();

                out.close();

                Drawable d = Drawable.createFromStream(i, "src");

                return loadImageFromUrl(url);

            } else {

                URL m = new URL(url);

                InputStream i = (InputStream) m.getContent();

                Drawable d = Drawable.createFromStream(i, "src");

                return d;

            }  

        }

    }

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