public class ErJiHuanCun extends ArrayAdapter<String> {  /**   * 記錄所有正在下載或等待下載的任務。   */  private Set<BitmapWorkerTask> taskCollection;  /**   * 圖片緩存技術的核心類，用于緩存所有下載好的圖片，在程序內存達到設定值時會將最少最近使用的圖片移除掉。   */  private LruCache<String, Bitmap> mMemoryCache;  /**   * 圖片硬盤緩存核心類。   */  private DiskLruCache mDiskLruCache;  /**   * GridView的實例   */  private GridView mPhotoWall;  /**   * 記錄每個子項的高度。   */  private int mItemHeight = 0;  public ErJiHuanCun(Context context, int textViewResourceId, String[] objects,      GridView photoWall) {    super(context, textViewResourceId, objects);    mPhotoWall = photoWall;    taskCollection = new HashSet<BitmapWorkerTask>();    // 獲取應用程序最大可用內存    int maxMemory = (int) Runtime.getRuntime().maxMemory();    int cacheSize = maxMemory / 8;    // 設置圖片緩存大小為程序最大可用內存的1/8    mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {      @Override      protected int sizeOf(String key, Bitmap bitmap) {        return bitmap.getByteCount();      }    };    try {      // 獲取圖片緩存路徑      File cacheDir = getDiskCacheDir(context, "thumb");      if (!cacheDir.exists()) {        cacheDir.mkdirs();      }      // 創建DiskLruCache實例，初始化緩存數據      mDiskLruCache = DiskLruCache          .open(cacheDir, getAppVersion(context), 1, 10 * 1024 * 1024);    } catch (IOException e) {      e.printStackTrace();    }  }  @Override  public View getView(int position, View convertView, ViewGroup parent) {    final String url = getItem(position);    View view;    if (convertView == null) {      view = LayoutInflater.from(getContext()).inflate(R.layout.photo_layout, null);    } else {      view = convertView;    }    final ImageView imageView = (ImageView) view.findViewById(R.id.photo);    if (imageView.getLayoutParams().height != mItemHeight) {      imageView.getLayoutParams().height = mItemHeight;    }    // 給ImageView設置一個Tag，保證異步加載圖片時不會亂序    imageView.setTag(url);     imageView.setImageResource(R.drawable.ic_launcher);    loadBitmaps(imageView, url);    return view;  }  /**   * 將一張圖片存儲到LruCache中。   *    * @param key   *      LruCache的鍵，這里傳入圖片的URL地址。   * @param bitmap   *      LruCache的鍵，這里傳入從網絡上下載的Bitmap對象。   */  public void addBitmapToMemoryCache(String key, Bitmap bitmap) {    if (getBitmapFromMemoryCache(key) == null) {      mMemoryCache.put(key, bitmap);    }  }  /**   * 從LruCache中獲取一張圖片，如果不存在就返回null。   *    * @param key   *      LruCache的鍵，這里傳入圖片的URL地址。   * @return 對應傳入鍵的Bitmap對象，或者null。   */  public Bitmap getBitmapFromMemoryCache(String key) {    return mMemoryCache.get(key);  }  /**   * 加載Bitmap對象。此方法會在LruCache中檢查所有屏幕中可見的ImageView的Bitmap對象，   * 如果發現任何一個ImageView的Bitmap對象不在緩存中，就會開啟異步線程去下載圖片。   */  public void loadBitmaps(ImageView imageView, String imageUrl) {    try {      Bitmap bitmap = getBitmapFromMemoryCache(imageUrl);      if (bitmap == null) {        BitmapWorkerTask task = new BitmapWorkerTask();        taskCollection.add(task);        task.execute(imageUrl);      } else {        if (imageView != null && bitmap != null) {          imageView.setImageBitmap(bitmap);        }      }    } catch (Exception e) {      e.printStackTrace();    }  }  /**   * 取消所有正在下載或等待下載的任務。   */  public void cancelAllTasks() {    if (taskCollection != null) {      for (BitmapWorkerTask task : taskCollection) {        task.cancel(false);      }    }  }  /**   * 根據傳入的uniqueName獲取硬盤緩存的路徑地址。   */  public File getDiskCacheDir(Context context, String uniqueName) {    String cachePath;    if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())        || !Environment.isExternalStorageRemovable()) {      cachePath = context.getExternalCacheDir().getPath();    } else {      cachePath = context.getCacheDir().getPath();    }    return new File(cachePath + File.separator + uniqueName);  }  /**   * 獲取當前應用程序的版本號。   */  public int getAppVersion(Context context) {    try {      PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(),          0);      return info.versionCode;    } catch (NameNotFoundException e) {      e.printStackTrace();    }    return 1;  }  /**   * 設置item子項的高度。   */  public void setItemHeight(int height) {    if (height == mItemHeight) {      return;    }    mItemHeight = height;    notifyDataSetChanged();  }  /**   * 使用MD5算法對傳入的key進行加密并返回。   */  public String hashKeyForDisk(String key) {    String cacheKey;    try {      final MessageDigest mDigest = MessageDigest.getInstance("MD5");      mDigest.update(key.getBytes());      cacheKey = bytesToHexString(mDigest.digest());    } catch (NoSuchAlgorithmException e) {      cacheKey = String.valueOf(key.hashCode());    }    return cacheKey;  }  /**   * 將緩存記錄同步到journal文件中。   */  public void flushCache() {    if (mDiskLruCache != null) {      try {        mDiskLruCache.flush();      } catch (IOException e) {        e.printStackTrace();      }    }  }  private String bytesToHexString(byte[] bytes) {    StringBuilder sb = new StringBuilder();    for (int i = 0; i < bytes.length; i++) {      String hex = Integer.toHexString(0xFF & bytes[i]);      if (hex.length() == 1) {        sb.append('0');      }      sb.append(hex);    }    return sb.toString();  }  /**   * 異步下載圖片的任務。   *    *   */  class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {    /**     * 圖片的URL地址     */    private String imageUrl;    @Override    protected Bitmap doInBackground(String... params) {      imageUrl = params[0];      FileDescriptor fileDescriptor = null;      FileInputStream fileInputStream = null;      Snapshot snapShot = null;      try {        // 生成圖片URL對應的key        final String key = hashKeyForDisk(imageUrl);        // 查找key對應的緩存        snapShot = mDiskLruCache.get(key);        if (snapShot == null) {          // 如果沒有找到對應的緩存，則準備從網絡上請求數據，并寫入緩存          DiskLruCache.Editor editor = mDiskLruCache.edit(key);          if (editor != null) {            OutputStream outputStream = editor.newOutputStream(0);            if (downloadUrlToStream(imageUrl, outputStream)) {              editor.commit();            } else {              editor.abort();            }          }          // 緩存被寫入后，再次查找key對應的緩存          snapShot = mDiskLruCache.get(key);        }        if (snapShot != null) {          fileInputStream = (FileInputStream) snapShot.getInputStream(0);          fileDescriptor = fileInputStream.getFD();        }        // 將緩存數據解析成Bitmap對象        Bitmap bitmap = null;        if (fileDescriptor != null) {        // bitmap = BitmapFactory.decodeFileDescriptor(fileDescriptor);         WindowManager wm= (WindowManager)getContext().getSystemService(Context.WINDOW_SERVICE);         int width=wm.getDefaultDisplay().getWidth();         bitmap= ImageResizer.decodeSampleBithmapFromFileDescriptor(fileDescriptor,width/3,width/3);        }        if (bitmap != null) {          // 將Bitmap對象添加到內存緩存當中            addBitmapToMemoryCache(params[0], bitmap);        }        return bitmap;      } catch (IOException e) {        e.printStackTrace();      } finally {        if (fileDescriptor == null && fileInputStream != null) {          try {            fileInputStream.close();          } catch (IOException e) {          }        }      }      return null;    }    @Override    protected void onPostExecute(Bitmap bitmap) {      super.onPostExecute(bitmap);      // 根據Tag找到相應的ImageView控件，將下載好的圖片顯示出來。      ImageView imageView = (ImageView) mPhotoWall.findViewWithTag(imageUrl);      if (imageView != null && bitmap != null) {        imageView.setImageBitmap(bitmap);      }      taskCollection.remove(this);    }    /**     * 建立HTTP請求，并獲取Bitmap對象。     *      * @param imageUrl     *      圖片的URL地址     * @return 解析后的Bitmap對象     */    private boolean downloadUrlToStream(String urlString, OutputStream outputStream) {      HttpURLConnection urlConnection = null;      BufferedOutputStream out = null;      BufferedInputStream in = null;      try {        final URL url = new URL(urlString);        urlConnection = (HttpURLConnection) url.openConnection();        in = new BufferedInputStream(urlConnection.getInputStream(), 8 * 1024);        out = new BufferedOutputStream(outputStream, 8 * 1024);        int b;        while ((b = in.read()) != -1) {          out.write(b);        }        return true;      } catch (final IOException e) {        e.printStackTrace();      } finally {        if (urlConnection != null) {          urlConnection.disconnect();        }        try {          if (out != null) {            out.close();          }          if (in != null) {            in.close();          }        } catch (final IOException e) {          e.printStackTrace();        }      }      return false;    }  }}

/** * 照片墻主活動，使用GridView展示照片墻。 *  *  */public class MainActivity extends Activity {  /**   * 用于展示照片墻的GridView   */  private GridView mPhotoWall;  /**   * GridView的適配器   */  private ErJiHuanCun mAdapter;  private int mImageThumbSize;  private int mImageThumbSpacing;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    //mImageThumbSize = getResources().getDimensionPixelSize(  //     R.dimen.image_thumbnail_size);    //mImageThumbSpacing = getResources().getDimensionPixelSize(  //     R.dimen.image_thumbnail_spacing);    mPhotoWall = (GridView) findViewById(R.id.photo_wall);    mAdapter = new ErJiHuanCun(this, 0, Images.imageThumbUrls,        mPhotoWall);    mPhotoWall.setAdapter(mAdapter);/*   mPhotoWall.getViewTreeObserver().addOnGlobalLayoutListener(        new ViewTreeObserver.OnGlobalLayoutListener() {          @Override          public void onGlobalLayout() {            final int numColumns = (int) Math.floor(mPhotoWall                .getWidth()                / (mImageThumbSize + mImageThumbSpacing));            if (numColumns > 0) {              int columnWidth = (mPhotoWall.getWidth() / numColumns)                  - mImageThumbSpacing;              mAdapter.setItemHeight(columnWidth);              mPhotoWall.getViewTreeObserver()                  .removeGlobalOnLayoutListener(this);            }          }        });*/  }  @Override  protected void onPause() {    super.onPause();    //將緩存記錄同步到journal文件中    mAdapter.flushCache();  }  @Override  protected void onDestroy() {    super.onDestroy();    // // 退出程序時結束所有的下載任務    mAdapter.cancelAllTasks();  }}

/** * 自定義正方形的ImageView *  */public class MyImageView extends ImageView {  public MyImageView(Context context, AttributeSet attrs, int defStyleAttr) {    super(context, attrs, defStyleAttr);    // TODO Auto-generated constructor stub  }  public MyImageView(Context context, AttributeSet attrs) {    super(context, attrs);    // TODO Auto-generated constructor stub  }  public MyImageView(Context context) {    super(context);    // TODO Auto-generated constructor stub  }  @Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  // TODO Auto-generated method stub    //將高度信息改成寬度即可  super.onMeasure(widthMeasureSpec, widthMeasureSpec);}}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:tools="http://schemas.android.com/tools"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:orientation="vertical"  android:padding="5dp" ><GridView  android:id="@+id/photo_wall"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:gravity="center"  android:horizontalSpacing="5dp"  android:verticalSpacing="5dp"  android:numColumns="3"  android:stretchMode="columnWidth"  /></LinearLayout>

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:orientation="vertical" ><com.example.imageloader.MyImageView  android:layout_width="match_parent"  android:layout_height="0dp"   android:id="@+id/photo"  /></LinearLayout>

public class ImageResizer { private static final String TAG="ImageResizer"; public static Bitmap decodeSampledBitmapFromResource(Resources res,     int resId,int reqWidth,int reqHeight){   final BitmapFactory.Options options=new BitmapFactory.Options();   options.inJustDecodeBounds=true;   BitmapFactory.decodeResource(res,resId,options);   options.inSampleSize=calculateInSampleSize(options,reqWidth,reqHeight);   options.inJustDecodeBounds=false;   return BitmapFactory.decodeResource(res, resId, options); } public static Bitmap decodeSampleBithmapFromFileDescriptor(FileDescriptor fd,     int reqWidth,int reqHeight){   final BitmapFactory.Options options=new BitmapFactory.Options();   options.inJustDecodeBounds=true;   BitmapFactory.decodeFileDescriptor(fd, null,options);   options.inSampleSize=calculateInSampleSize(options,reqWidth,reqHeight);   options.inJustDecodeBounds=false;   return BitmapFactory.decodeFileDescriptor(fd, null,options); } public static int calculateInSampleSize(BitmapFactory.Options options,     int reqWidth,int reqHeight){   if(reqWidth==0||reqHeight==0)     return 1;   final int width=options.outWidth;   final int height=options.outHeight;   int inSampleSize=1;   if(height>reqHeight||width>reqWidth  ){     final int halfHeight=height/2;     final int halfWidth=width/2;     //盡最大限度的壓縮圖片，不能讓圖片的寬高比ImageView的寬高小，否則在將     //圖片顯示到ImageView時，圖片會放大導致圖片失真   while(halfHeight/inSampleSize>reqHeight&&halfWidth/inSampleSize>reqWidth){      inSampleSize*=2;    }   }   return inSampleSize; }}