异步下载图片+图片缓存
代码参考自:jamendo,有一定修改。
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功能如下：
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流程如下：
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?? RemoteImageViewActivity:
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public class RemoteImageViewActivity extends Activity {/** Called when the activity is first created. */@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.main);RemoteImageView img = (RemoteImageView) findViewById(R.id.remote_img);img.setDefaultImage(R.drawable.ic_launcher);img.setImageUrl("http://img2.kwcdn.kuwo.cn:81/star/albumcover/120/7/8/83787_1323997225.jpg");}@Overrideprotected void onPause() {// TODO Auto-generated method stubsuper.onPause();}}?
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? ImageCache:
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public class ImageCache extends WeakHashMap<String, Bitmap>{/** * 判断该url是否存在 * @param url * @return */public boolean isCached(String url){return containsKey(url) && get(url) != null;}}?
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?? RemoteImageApplication:
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public class RemoteImageApplication extends Application {public static final String TAG = "RemoteImageApplication";private static RemoteImageApplication application;private ImageCache mImageCache;public SharedPreferences prefs = null;public static RemoteImageApplication getInstance() {return application;}@Overridepublic void onCreate() {// TODO Auto-generated method stubsuper.onCreate();application = this;mImageCache = new ImageCache();prefs = PreferenceManager.getDefaultSharedPreferences(this);}public ImageCache getImageCache() {return mImageCache;}}?
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??? RemoteSettings:
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public class RemoteSettings {public static final String CACHE_SIZE = "cache_size"; //图片缓存保留大小,如果超过该大小，即进行自动清除缓存.}???
?? RemoteImageView:
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public class RemoteImageView extends ImageView {private Context mContext;private static int mCacheSize = 150; // 设置的缓存大小。private static final int MAX_FAILURES = 3; // 下载的尝试请求次数private int mFailure; // 下载失败次数private String mUrl; // 当前下载的urlprivate String mCurrentlyGrabbedUrl; // 当前下载成功的urlprivate final static String JAMENDO_DIR = "Android/data/com.teleca.jamendo"; // 文件缓存存放的路径.private final static long MB = 1073741824;public RemoteImageView(Context context, AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);mContext = context;}public RemoteImageView(Context context, AttributeSet attrs) {super(context, attrs);mContext = context;}public RemoteImageView(Context context) {super(context);mContext = context;}/** * 设置默认图片 */public void setDefaultImage(Integer resid) {setImageResource(resid);}/** * 设置需要异步加载的图片 */public void setImageUrl(String url) {// 下载失败进行重试,如果重试次数超过规定的限制，则直接返回.if (mUrl != null&& mUrl.equals(url)&& (mCurrentlyGrabbedUrl == null || (mCurrentlyGrabbedUrl != null && !mCurrentlyGrabbedUrl.equals(url)))) {mFailure++;if (mFailure > MAX_FAILURES) {Log.e(RemoteImageApplication.TAG, "下载该图片地址失败:" + url);return;}} else {mUrl = url;mFailure = 0;}ImageCache imageCache = RemoteImageApplication.getInstance().getImageCache();if (imageCache.isCached(url)) {setImageBitmap(imageCache.get(url));} else {// 如果内存中没有该缓存，则从文件中进行查找.String fileName = convertUrlToFileName(url); // 进行文件名处理String filepath = getDirectory(fileName); // 取得缓存文件夹目录String pathFileName = filepath + "/" + fileName; // 组拼文件File pathFile = new File(pathFileName);if (!pathFile.exists()) {try {pathFile.createNewFile();} catch (IOException e) {Log.d(RemoteImageApplication.TAG, "创建图片文件失败:"+ pathFileName);}}Bitmap tbmp = BitmapFactory.decodeFile(pathFileName);if (tbmp == null) {Log.d(RemoteImageApplication.TAG, "图片文件不存在，开始进行下载");try {new DownloadTask().execute(url);} catch (RejectedExecutionException e) {Log.d(RemoteImageApplication.TAG, "下载失败");}} else {Log.i(RemoteImageApplication.TAG, "从文件中加载图片");RemoteImageApplication.getInstance().getImageCache().put(url, tbmp);this.setImageBitmap(tbmp);}updateCacheSize(pathFileName); // 进行检测文件大小,以便于清除缓存.}}private void updateCacheSize(String pathFileName) {// TODO Auto-generated method stubupdateSizeCache(pathFileName);}/** * 检查文件目录是否超过规定的缓存大小 * * @param fileName */private void updateSizeCache(String pathFileName) {// TODO Auto-generated method stubmCacheSize = PreferenceManager.getDefaultSharedPreferences(mContext).getInt(RemoteSettings.CACHE_SIZE, 100); // 读取设置的缓存大小，前台可以动态设置此值if (isSDCardEnable()) {String extStorageDirectory = Environment.getExternalStorageDirectory().toString(); // 取得SD根路径String dirPath = extStorageDirectory + "/" + JAMENDO_DIR+ "/imagecache";File dirFile = new File(dirPath);File[] files = dirFile.listFiles();long dirSize = 0;for (File file : files) {dirSize += file.length();}if (dirSize > mCacheSize * MB) {clearCache();}}}/** * 异步下载图片 * * @ClassName: DownloadTask * @author 姜涛 * @version 1.0 2012-1-15 下午5:06:21 */class DownloadTask extends AsyncTask<String, Void, String> {private String mTaskUrl;private Bitmap mBmp = null;@Overridepublic void onPreExecute() {// loadDefaultImage();super.onPreExecute();}@Overridepublic String doInBackground(String... params) {mTaskUrl = params[0];InputStream stream = null;URL imageUrl;Bitmap bmp = null;try {imageUrl = new URL(mTaskUrl);try {stream = imageUrl.openStream();bmp = BitmapFactory.decodeStream(stream);try {if (bmp != null) {mBmp = bmp;RemoteImageApplication.getInstance().getImageCache().put(mTaskUrl, bmp);Log.d(RemoteImageApplication.TAG,"图片缓存到application中: " + mTaskUrl);}} catch (NullPointerException e) {Log.w(RemoteImageApplication.TAG, "下载失败，图片为空:"+ mTaskUrl);}} catch (IOException e) {Log.w(RemoteImageApplication.TAG, "无法加载该url:" + mTaskUrl);} finally {try {if (stream != null) {stream.close();}} catch (IOException e) {}}} catch (MalformedURLException e) {e.printStackTrace();}return mTaskUrl;}@Overridepublic void onPostExecute(String url) {super.onPostExecute(url);Bitmap bmp = RemoteImageApplication.getInstance().getImageCache().get(url);if (bmp == null) {Log.w(RemoteImageApplication.TAG, "尝试重新下载:" + url);RemoteImageView.this.setImageUrl(url);} else {RemoteImageView.this.setImageBitmap(bmp);mCurrentlyGrabbedUrl = url;saveBmpToSd(mBmp, url);}}};/** * 把图片保存到本地 * * @param bm * @param url */private void saveBmpToSd(Bitmap bm, String url) {if (bm == null) {return;}if (mCacheSize == 0) {return;}String filename = convertUrlToFileName(url);String dir = getDirectory(filename);File file = new File(dir + "/" + filename);try {file.createNewFile();OutputStream outStream = new FileOutputStream(file);bm.compress(Bitmap.CompressFormat.JPEG, 100, outStream);outStream.flush();outStream.close();Log.i(RemoteImageApplication.TAG, "图片已保存到sd卡");} catch (FileNotFoundException e) {Log.w(RemoteImageApplication.TAG, "无法找到文件目录");} catch (IOException e) {Log.w(RemoteImageApplication.TAG, "操作文件出错");}}/** * 组拼文件名，后缀名用dat代替，避免别人使用图片管理器搜索出这种对于她们无用的图片. * * @param url * @return */private String convertUrlToFileName(String url) {String filename = url;filename = filename.replace("http://", "");filename = filename.replace("/", ".");filename = filename.replace(":", ".");filename = filename.replace("jpg", "dat");filename = filename.replace("png", "dat");return filename;}/** * 返回缓存图片所存放的文件夹 * * @param filename * @return */private String getDirectory(String filename) {String extStorageDirectory = Environment.getExternalStorageDirectory().toString(); // 取得SD根路径String dirPath = extStorageDirectory + "/" + JAMENDO_DIR+ "/imagecache";File dirFile = new File(dirPath);if (!dirFile.exists()) {dirFile.mkdirs();}return dirPath;}/** * 清除缓存 */private void clearCache() {if (isSDCardEnable()) {String extStorageDirectory = Environment.getExternalStorageDirectory().toString(); // 取得SD根路径String dirPath = extStorageDirectory + "/" + JAMENDO_DIR+ "/imagecache";File dir = new File(dirPath);File[] files = dir.listFiles(); // 取得该目录下的所有文件if (files == null || files.length == 0) {return;}for (File file : files) {file.delete();}Log.d(RemoteImageApplication.TAG, "已清除缓存:" + dirPath);}}/** * 判断SD卡是否可用 */public static boolean isSDCardEnable() {return Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED);}}?
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?代码参见附件.
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