我正在做一个关于图像的应用程序,以便在GridView中显示它们,我正在从服务器获取20个图像。每个图像的分辨率是720*540。我使用JSON解析来获取url,并使用下面的代码转换为位图来设置图像。
public static Bitmap loadImageFromUrl(String url) {
InputStream inputStream;Bitmap b;
try {
inputStream = (InputStream) new URL(url).getContent();
BitmapFactory.Options bpo= new BitmapFactory.Options();
if(bpo.outWidth>500) {
bpo.inSampleSize=8;
b=BitmapFactory.decodeStream(inputStream, null,bpo );
} else {
bpo.inSampleSize=2;
b=BitmapFactory.decodeStream(inputStream, null,bpo );
}
return b;
} catch (IOException e) {
throw new RuntimeException(e);
}
}
我的应用程序运行良好,但加载图像花费了太多时间。所以我的应用程序变得很慢。我应该降低图像的分辨率吗?
如何解决这个问题?
如果你正在进行网格视图以加载20张这样分辨率的图像,我建议如下:
-
一定要缩小图像的大小。除非你的目标是平板电脑,否则你会没事的,因为大多数智能手机都无法在20张图像的情况下达到这个分辨率。
-
如果可以,请缓存图像。
-
在其他线程上下载图像。存储一个HashMap对您来说很容易,只需将所有带有图像文件名或其他形式ID的图像视图作为键即可。在下载图像时向处理程序发送消息,并在解码后更新视图。您可以直接检索视图。只要记得检查一下它们是否还在窗户里。通过这种方式,图像将一个接一个地快速显示出来。我不认为多线程处理图像会有帮助,只是确保使用另一个线程来"推送图像"和主UI线程更新。届时,用户体验将大大改善。
希望这能有所帮助。
---在一些实现中,我现在没有完整的代码---
有一个数据结构来匹配视图和附带的数据。在这里非常方便。
private HashMap<String,ImageView> pictures;
当你得到图像url的列表时,迭代它们:
pictures.put(id,view);
try{
FileInputStream in = openFileInput(id);
Bitmap bitmap = null;
bitmap = BitmapFactory.decodeStream(in, null, null);
view.setImageBitmap(bitmap);
}catch(Exception e){
new Thread(new PictureGetter(this,mHandler,id)).start();
}
(在这里,如果图像尚未缓存,图片获取器将简单地获取图像并缓存它(
更新图像视图的代码:
if(id!=null){
ImageView iv = pictures.get(id);
if(iv!=null){
try{
FileInputStream in = openFileInput(id);
Bitmap bitmap = null;
bitmap = BitmapFactory.decodeStream(in, null, null);
iv.setImageBitmap(bitmap);
}catch(Exception e){
}
}
毕加索图书馆
解决方案是使用位图直接加载图像,而不是使用一个名为Picasso的很棒的库,它的速度非常快,我知道你真的很喜欢这个,你可以这样做
将picassojar文件添加到您的项目中(在此处下载picassoJAR文件(使用picasso加载像这样的图像
Picasso.with(context).load(new File(title)).centerCrop()
.resize(150, 150).error(R.drawable.ic_launcher).into(image);
其中title是要加载的图像路径。裁剪、调整大小和错误都是可选的。
我猜大部分加载时间是因为大量的图像加上图像的大小。
有两种可能的解决方案:
-
调整图像大小,或降低图像质量,使文件大小低于75kb左右。
-
使用多线程一次检索多个图像。如果用户的连接真的很慢,这可能没有帮助,但如果你把它与足够小的文件大小结合起来,它可能就足够了。您可能需要确定设备的当前带宽,并以此为基础运行线程数。
例如:每个75KB的20个映像和200KB/s的可用连接=3或4个并发线程。
希望这能有所帮助。
我的android应用程序中也有同样的问题。当你从大尺寸图像中解码位图并将其设置为imageBitmap到图像视图时,你的应用程序可能会变慢,经过几次尝试后,你会得到"内存不足异常">
有两种可能的方法可以尝试处理此问题:1-从文件解码时减小位图大小2-使用图像库。
我更喜欢第二种方式,并使用了通用图像加载器。https://github.com/nostra13/Android-Universal-Image-Loader
String url = "file://" + your_file_path
com.nostra13.universalimageloader.core.ImageLoader.getInstance().displayImage(url, ivPicture, options);
public class clothImageLoader {
// the simplest in-memory cache implementation. This should be replaced with
// something like SoftReference or BitmapOptions.inPurgeable(since 1.6)
// public static HashMap<String, Bitmap> cache = new HashMap<String,
// Bitmap>();
private static File cacheDir;
public clothImageLoader(Context context) {
// Make the background thead low priority. This way it will not affect
// the UI performance
photoLoaderThread.setPriority(Thread.NORM_PRIORITY - 1);
// Find the dir to save cached images
if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
// cacheDir=new
// File(android.os.Environment.getExternalStorageDirectory(),"LazyList");
cacheDir = new File(ConstValue.MY_ClothBitmap_DIR);
else
cacheDir = context.getCacheDir();
if (!cacheDir.exists())
cacheDir.mkdirs();
}
final int stub_id = R.drawable.icon;
public void DisplayImage(String url, Activity activity, ImageView imageView) {
if (ConstValue.ClothRoomcache.containsKey(url))
imageView.setImageBitmap(ConstValue.ClothRoomcache.get(url));
else {
queuePhoto(url, activity, imageView);
imageView.setImageResource(stub_id);
}
}
private void queuePhoto(String url, Activity activity, ImageView imageView) {
// This ImageView may be used for other images before. So there may be
// some old tasks in the queue. We need to discard them.
photosQueue.Clean(imageView);
PhotoToLoad p = new PhotoToLoad(url, imageView);
synchronized (photosQueue.photosToLoad) {
photosQueue.photosToLoad.push(p);
photosQueue.photosToLoad.notifyAll();
}
// start thread if it's not started yet
if (photoLoaderThread.getState() == Thread.State.NEW)
photoLoaderThread.start();
}
private Bitmap getBitmap(String url) {
// I identify images by hashcode. Not a perfect solution, good for the
// demo.
String filename = String.valueOf(url.hashCode());
File f = new File(cacheDir, filename);
// from SD cache
Bitmap b = decodeFile(f);
if (b != null)
return b;
// from web
try {
Bitmap bitmap = null;
/*
* InputStream is=new URL(url).openStream(); OutputStream os = new
* FileOutputStream(f); Utils.CopyStream(is, os); os.close();
*/
URL url1 = new URL(url);
bitmap = decodeFile(f);
/* Open a connection to that URL. */
URLConnection ucon = url1.openConnection();
/*
* Define InputStreams to read from the URLConnection.
*/
InputStream is = ucon.getInputStream();
// FlushedInputStream a = new FlushedInputStream(is);
BufferedInputStream bis = new BufferedInputStream(is);
/*
* Read bytes to the Buffer until there is nothing more to read(-1).
*/
ByteArrayBuffer baf = new ByteArrayBuffer(5000);
int current = 0;
while ((current = bis.read()) != -1) {
baf.append((byte) current);
}
/* Convert the Bytes read to a String. */
FileOutputStream fos = new FileOutputStream(f);
fos.write(baf.toByteArray());
fos.flush();
fos.close();
bitmap = decodeFile(f);
return bitmap;
} catch (Exception ex) {
ex.printStackTrace();
return null;
}
}
// decodes image and scales it to reduce memory consumption
private Bitmap decodeFile(File f) {
try {
// decode image size
BitmapFactory.Options o = new BitmapFactory.Options();
o.inJustDecodeBounds = true;
BitmapFactory.decodeStream(new FileInputStream(f), null, o);
// Find the correct scale value. It should be the power of 2.
final int REQUIRED_SIZE = ConstValue.bmpSize;
int width_tmp = o.outWidth, height_tmp = o.outHeight;
int scale = 1;
while (true) {
if (width_tmp / 2 < REQUIRED_SIZE || height_tmp / 2 < REQUIRED_SIZE)
break;
width_tmp /= 2;
height_tmp /= 2;
scale++;
}
// decode with inSampleSize
BitmapFactory.Options o2 = new BitmapFactory.Options();
o2.inSampleSize = scale;
return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
} catch (FileNotFoundException e) {
}
return null;
}
// Task for the queue
private class PhotoToLoad {
public String url;
public ImageView imageView;
public PhotoToLoad(String u, ImageView i) {
url = u;
imageView = i;
}
}
PhotosQueue photosQueue = new PhotosQueue();
public void stopThread() {
photoLoaderThread.interrupt();
}
// stores list of photos to download
class PhotosQueue {
private Stack<PhotoToLoad> photosToLoad = new Stack<PhotoToLoad>();
// removes all instances of this ImageView
public void Clean(ImageView image) {
for (int j = 0; j < photosToLoad.size();) {
if (photosToLoad.get(j).imageView == image)
photosToLoad.remove(j);
else
++j;
}
}
}
class PhotosLoader extends Thread {
public void run() {
try {
while (true) {
// thread waits until there are any images to load in the
// queue
if (photosQueue.photosToLoad.size() == 0)
synchronized (photosQueue.photosToLoad) {
photosQueue.photosToLoad.wait();
}
if (photosQueue.photosToLoad.size() != 0) {
PhotoToLoad photoToLoad;
synchronized (photosQueue.photosToLoad) {
photoToLoad = photosQueue.photosToLoad.pop();
// photoToLoad=photosQueue.photosToLoad.get(0);
// photosQueue.photosToLoad.remove(photoToLoad);
}
Bitmap bmp = getBitmap(photoToLoad.url);
ConstValue.ClothRoomcache.put(photoToLoad.url, bmp);
if (((String) photoToLoad.imageView.getTag()).equals(photoToLoad.url)) {
BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad.imageView);
Activity a = (Activity) photoToLoad.imageView.getContext();
a.runOnUiThread(bd);
}
}
if (Thread.interrupted())
break;
}
} catch (InterruptedException e) {
// allow thread to exit
}
}
}
PhotosLoader photoLoaderThread = new PhotosLoader();
// Used to display bitmap in the UI thread
class BitmapDisplayer implements Runnable {
Bitmap bitmap;
ImageView imageView;
public BitmapDisplayer(Bitmap b, ImageView i) {
bitmap = b;
imageView = i;
}
public void run() {
if (bitmap != null)
imageView.setImageBitmap(bitmap);
else
imageView.setImageResource(stub_id);
}
}
public static void clearCache() {
// clear memory cache
ConstValue.ClothRoomcache.clear();
// clear SD cache
File[] files = cacheDir.listFiles();
for (File f : files)
f.delete();
}
public class FlushedInputStream extends FilterInputStream {
public FlushedInputStream(InputStream inputStream) {
super(inputStream);
}
@Override
public long skip(long n) throws IOException {
long totalBytesSkipped = 0L;
while (totalBytesSkipped < n) {
long bytesSkipped = in.skip(n - totalBytesSkipped);
if (bytesSkipped == 0L) {
int a = read();
if (a < 0) {
break; // we reached EOF
} else {
bytesSkipped = 1; // we read one byte
}
}
totalBytesSkipped += bytesSkipped;
}
return totalBytesSkipped;
}
}
}
当您调用该方法时,在gridView的getView方法中:
holder.image.setTag(ChoseInfo.get(position).getLink());
imageLoader.DisplayImage(ChoseInfo.get(position).getLink(), activity, holder.image);
ChoseInfo.get(position(.getLink((
这里getLink()
是互联网链接。