异步下载图片和图片缓存
功能如下：
流程如下：
RemoteImageViewActivity:
public class RemoteImageViewActivity extends Activity {
/** Called when the activity is first created. */
@Override
public 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");
}
@Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
}
} ImageCache:
public class ImageCache extends WeakHashMap{
/**
* 判断该url是否存在
* @param url
* @return
*/
public boolean isCached(String url){
return containsKey(url) && get(url) != null;
}
} RemoteImageApplication:
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;
}
@Override
public void onCreate() {
// TODO Auto-generated method stub
super.onCreate();
application = this;
mImageCache = new ImageCache();
prefs = PreferenceManager.getDefaultSharedPreferences(this);
}
public ImageCache getImageCache() {
return mImageCache;
}
} RemoteSettings:
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:
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url
private String mCurrentlyGrabbedUrl; // 当前下载成功的url
private 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 stub
updateSizeCache(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 stub
mCacheSize = 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 {
private String mTaskUrl;
private Bitmap mBmp = null;
@Override
public void onPreExecute() {
// loadDefaultImage();
super.onPreExecute();
}
@Override
public 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;
}
@Override
public 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);
}
} 本文转自：http://lewisliu.iteye.com/blog/1346820