Android中的缓存处理及异步加载图片类的封装

• 1.命中率；
• 2.合理分配占用的空间；
• 3.合理的缓存层级。

publicclass ImageDownloadHelper {

privatestaticfinal String TAG = "ImageDownloaderHelper";

private HashMap<String, MyAsyncTask> map = new HashMap<String, MyAsyncTask>();

private Map<String, SoftReference<Bitmap>> softCaches = new LinkedHashMap<String, SoftReference<Bitmap>>();

private LruCache<String, Bitmap> lruCache = null;

public ImageDownloadHelper() {

int memoryAmount = (int) Runtime.getRuntime().maxMemory();

// 获取剩余内存的8分之一作为缓存

int cacheSize = memoryAmount / 8;

if (lruCache == null) {

lruCache = new MyLruCache(cacheSize);

}

Log.i(TAG, "==LruCache尺寸：" + cacheSize);

}

/**

 * 

 * @param context

 * @param url

 * 该mImageView对应的url

 * @param mImageView

 * @param path

 * 文件存储路径

 * @param downloadListener

 * OnImageDownload回调接口，在onPostExecute()中被调用

 */

publicvoid imageDownload(Context context, String url,

ImageView mImageView, String path,

OnImageDownloadListener downloadListener) {

Bitmap bitmap = null;

// 先从强引用中拿数据

if (lruCache != null) {

bitmap = lruCache.get(url);

}

if (bitmap != null && url.equals(mImageView.getTag())) {

Log.i(TAG, "==从强引用中找到数据");

mImageView.setImageBitmap(bitmap);

} else {

SoftReference<Bitmap> softReference = softCaches.get(url);

if (softReference != null) {

bitmap = softReference.get();

}

// 从软引用中拿数据

if (bitmap != null && url.equals(mImageView.getTag())) {

Log.i(TAG, "==从软引用中找到数据");

// 添加到强引用中

lruCache.put(url, bitmap);

Log.i(TAG, "==添加到强引用中");

// 从软引用集合中移除

softCaches.remove(url);

mImageView.setImageBitmap(bitmap);

} else {

// 从文件缓存中拿数据

String imageName = "";

if (url != null) {

imageName = ImageDownloaderUtil.getInstance().getImageName(

url);

}

bitmap = getBitmapFromFile(context, imageName, path);

if (bitmap != null && url.equals(mImageView.getTag())) {

Log.i(TAG, "==从文件缓存中找到数据");

// 放入强缓存

lruCache.put(url, bitmap);

mImageView.setImageBitmap(bitmap);

} else {

// 从网络中拿数据

if (url != null && needCreateNewTask(mImageView)) {

MyAsyncTask task = new MyAsyncTask(context, url,

mImageView, path, downloadListener);

Log.i(TAG, "==从网络中拿数据");

if (mImageView != null) {

task.execute();

// 将对应的url对应的任务存起来

map.put(url, task);

}

}

}

}

}

}

/**

 * 判断是否需要重新创建线程下载图片，如果需要，返回值为true。

 * 

 * @param url

 * @param mImageView

 * @return

 */

privateboolean needCreateNewTask(ImageView mImageView) {

boolean b = true;

if (mImageView != null) {

String curr_task_url = (String) mImageView.getTag();

if (isTasksContains(curr_task_url)) {

b = false;

}

}

return b;

}

/**

 * 检查该url（最终反映的是当前的ImageView的tag，tag会根据position的不同而不同）对应的task是否存在

 * 

 * @param url

 * @return

 */

privateboolean isTasksContains(String url) {

boolean b = false;

if (map != null && map.get(url) != null) {

b = true;

}

return b;

}

/**

 * 删除map中该url的信息，这一步很重要，不然MyAsyncTask的引用会“一直”存在于map中

 * 

 * @param url

 */

privatevoid removeTaskFromMap(String url) {

if (url != null && map != null && map.get(url) != null) {

map.remove(url);

Log.i(TAG, "当前map的大小==" + map.size());

}

}

/**

 * 从文件中拿图片

 * 

 * @param mActivity

 * @param imageName

 * 图片名字

 * @param path

 * 图片路径

 * @return

 */

private Bitmap getBitmapFromFile(Context context, String imageName,

String path) {

Bitmap bitmap = null;

if (imageName != null) {

File file = null;

String real_path = "";

try {

if (ImageDownloaderUtil.getInstance().hasSDCard()) {

real_path = ImageDownloaderUtil.getInstance().getExtPath()

+ (path != null && path.startsWith("/") ? path

: "/" + path);

} else {

real_path = ImageDownloaderUtil.getInstance()

.getPackagePath(context)

+ (path != null && path.startsWith("/") ? path

: "/" + path);

}

file = new File(real_path, imageName);

if (file.exists())

bitmap = BitmapFactory.decodeStream(new FileInputStream(

file));

} catch (Exception e) {

e.printStackTrace();

bitmap = null;

}

}

return bitmap;

}

/**

 * 将下载好的图片存放到文件中

 * 

 * @param path

 * 图片路径

 * @param mActivity

 * @param imageName

 * 图片名字

 * @param bitmap

 * 图片

 * @return

 */

privateboolean setBitmapToFile(String path, Context mActivity,

String imageName, Bitmap bitmap) {

File file = null;

String real_path = "";

try {

if (ImageDownloaderUtil.getInstance().hasSDCard()) {

real_path = ImageDownloaderUtil.getInstance().getExtPath()

+ (path != null && path.startsWith("/") ? path : "/"

+ path);

} else {

real_path = ImageDownloaderUtil.getInstance().getPackagePath(

mActivity)

+ (path != null && path.startsWith("/") ? path : "/"

+ path);

}

file = new File(real_path, imageName);

if (!file.exists()) {

File file2 = new File(real_path + "/");

file2.mkdirs();

}

file.createNewFile();

FileOutputStream fos = null;

if (ImageDownloaderUtil.getInstance().hasSDCard()) {

fos = new FileOutputStream(file);

} else {

fos = mActivity.openFileOutput(imageName, Context.MODE_PRIVATE);

}

if (imageName != null

&& (imageName.contains(".png") || imageName

.contains(".PNG"))) {

bitmap.compress(Bitmap.CompressFormat.PNG, 90, fos);

} else {

bitmap.compress(Bitmap.CompressFormat.JPEG, 90, fos);

}

fos.flush();

if (fos != null) {

fos.close();

}

returntrue;

} catch (Exception e) {

e.printStackTrace();

returnfalse;

}

}

/**

 * 辅助方法，一般不调用

 * 

 * @param path

 * @param mActivity

 * @param imageName

 */

privatevoid removeBitmapFromFile(String path, Context mActivity,

String imageName) {

File file = null;

String real_path = "";

try {

if (ImageDownloaderUtil.getInstance().hasSDCard()) {

real_path = ImageDownloaderUtil.getInstance().getExtPath()

+ (path != null && path.startsWith("/") ? path : "/"

+ path);

} else {

real_path = ImageDownloaderUtil.getInstance().getPackagePath(

mActivity)

+ (path != null && path.startsWith("/") ? path : "/"

+ path);

}

file = new File(real_path, imageName);

if (file != null)

file.delete();

} catch (Exception e) {

e.printStackTrace();

}

}