wemall app商城源码Android之ListView异步加载网络图片(优化缓存机制)

thomas0yang 2019-06-21

wemall-mobile是基于WeMall的android app商城,只需要在原商城目录下上传接口文件即可完成服务端的配置,客户端可定制修改。本文分享wemall app商城源码Android之ListView异步加载网络图片(优化缓存机制)代码信息,供技术员参考学习。

1、采用线程池
2、内存缓存+文件缓存
3、内存缓存中网上很多是采用SoftReference来防止堆溢出,这儿严格限制只能使用最大JVM内存的1/4
4、对下载的图片进行按比例缩放,以减少内存的消耗
具体的代码里面说明。先放上内存缓存类的代码MemoryCache.java:

public class MemoryCache {

    private static final String TAG = "MemoryCache";
    // 放入缓存时是个同步操作
    // LinkedHashMap构造方法的最后一个参数true代表这个map里的元素将按照最近使用次数由少到多排列,即LRU
    // 这样的好处是如果要将缓存中的元素替换,则先遍历出最近最少使用的元素来替换以提高效率
    private Map<String, Bitmap> cache = Collections
            .synchronizedMap(new LinkedHashMap<String, Bitmap>(10, 1.5f, true));
    // 缓存中图片所占用的字节,初始0,将通过此变量严格控制缓存所占用的堆内存
    private long size = 0;// current allocated size
    // 缓存只能占用的最大堆内存
    private long limit = 1000000;// max memory in bytes

    public MemoryCache() {
        // use 25% of available heap size
        setLimit(Runtime.getRuntime().maxMemory() / 4);
    }

    public void setLimit(long new_limit) { 
        limit = new_limit;
        Log.i(TAG, "MemoryCache will use up to " + limit / 1024. / 1024. + "MB");
    }

    public Bitmap get(String id) {
        try {
            if (!cache.containsKey(id))
                return null;
            return cache.get(id);
        } catch (NullPointerException ex) {
            return null;
        }
    }

    public void put(String id, Bitmap bitmap) {
        try {
            if (cache.containsKey(id))
                size -= getSizeInBytes(cache.get(id));
            cache.put(id, bitmap);
            size += getSizeInBytes(bitmap);
            checkSize();
        } catch (Throwable th) {
            th.printStackTrace();
        }
    }

    /**
     * 严格控制堆内存,如果超过将首先替换最近最少使用的那个图片缓存
     * 
     */
    private void checkSize() {
        Log.i(TAG, "cache size=" + size + " length=" + cache.size());
        if (size > limit) {
            // 先遍历最近最少使用的元素
            Iterator<Entry<String, Bitmap>> iter = cache.entrySet().iterator();
            while (iter.hasNext()) {
                Entry<String, Bitmap> entry = iter.next();
                size -= getSizeInBytes(entry.getValue());
                iter.remove();
                if (size <= limit)
                    break;
            }
            Log.i(TAG, "Clean cache. New size " + cache.size());
        }
    }

    public void clear() {
        cache.clear();
    }

    /**
     * 图片占用的内存
     * 
     * @param bitmap
     * @return
     */
    long getSizeInBytes(Bitmap bitmap) {
        if (bitmap == null)
            return 0;
        return bitmap.getRowBytes() * bitmap.getHeight();
    }
}

也可以使用SoftReference,代码会简单很多,但是我推荐上面的方法。

public class MemoryCache {
    
    private Map<String, SoftReference<Bitmap>> cache = Collections
            .synchronizedMap(new HashMap<String, SoftReference<Bitmap>>());

    public Bitmap get(String id) {
        if (!cache.containsKey(id))
            return null;
        SoftReference<Bitmap> ref = cache.get(id);
        return ref.get();
    }

    public void put(String id, Bitmap bitmap) {
        cache.put(id, new SoftReference<Bitmap>(bitmap));
    }

    public void clear() {
        cache.clear();
    }

}

下面是文件缓存类的代码FileCache.java:

public class FileCache {

    private File cacheDir;

    public FileCache(Context context) {
        // 如果有SD卡则在SD卡中建一个LazyList的目录存放缓存的图片
        // 没有SD卡就放在系统的缓存目录中
        if (android.os.Environment.getExternalStorageState().equals(
                android.os.Environment.MEDIA_MOUNTED))
            cacheDir = new File(
                    android.os.Environment.getExternalStorageDirectory(),
                    "LazyList");
        else
            cacheDir = context.getCacheDir();
        if (!cacheDir.exists())
            cacheDir.mkdirs();
    }

    public File getFile(String url) {
        // 将url的hashCode作为缓存的文件名
        String filename = String.valueOf(url.hashCode());
        // Another possible solution
        // String filename = URLEncoder.encode(url);
        File f = new File(cacheDir, filename);
        return f;

    }

    public void clear() {
        File[] files = cacheDir.listFiles();
        if (files == null)
            return;
        for (File f : files)
            f.delete();
    }

}

最后最重要的加载图片的类,ImageLoader.java:

public class ImageLoader {

    MemoryCache memoryCache = new MemoryCache();
    FileCache fileCache;
    private Map<ImageView, String> imageViews = Collections
            .synchronizedMap(new WeakHashMap<ImageView, String>());
    // 线程池
    ExecutorService executorService;

    public ImageLoader(Context context) {
        fileCache = new FileCache(context);
        executorService = Executors.newFixedThreadPool(5);
    }

    // 当进入listview时默认的图片,可换成你自己的默认图片
    final int stub_id = R.drawable.stub;

    // 最主要的方法
    public void DisplayImage(String url, ImageView imageView) {
        imageViews.put(imageView, url);
        // 先从内存缓存中查找

        Bitmap bitmap = memoryCache.get(url);
        if (bitmap != null)
            imageView.setImageBitmap(bitmap);
        else {
            // 若没有的话则开启新线程加载图片
            queuePhoto(url, imageView);
            imageView.setImageResource(stub_id);
        }
    }

    private void queuePhoto(String url, ImageView imageView) {
        PhotoToLoad p = new PhotoToLoad(url, imageView);
        executorService.submit(new PhotosLoader(p));
    }

    private Bitmap getBitmap(String url) {
        File f = fileCache.getFile(url);

        // 先从文件缓存中查找是否有
        Bitmap b = decodeFile(f);
        if (b != null)
            return b;

        // 最后从指定的url中下载图片
        try {
            Bitmap bitmap = null;
            URL imageUrl = new URL(url);
            HttpURLConnection conn = (HttpURLConnection) imageUrl
                    .openConnection();
            conn.setConnectTimeout(30000);
            conn.setReadTimeout(30000);
            conn.setInstanceFollowRedirects(true);
            InputStream is = conn.getInputStream();
            OutputStream os = new FileOutputStream(f);
            CopyStream(is, os);
            os.close();
            bitmap = decodeFile(f);
            return bitmap;
        } catch (Exception ex) {
            ex.printStackTrace();
            return null;
        }
    }

    // decode这个图片并且按比例缩放以减少内存消耗,虚拟机对每张图片的缓存大小也是有限制的
    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 = 70;
            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 *= 2;
            }

            // 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;
        }
    }

    class PhotosLoader implements Runnable {
        PhotoToLoad photoToLoad;

        PhotosLoader(PhotoToLoad photoToLoad) {
            this.photoToLoad = photoToLoad;
        }

        @Override
        public void run() {
            if (imageViewReused(photoToLoad))
                return;
            Bitmap bmp = getBitmap(photoToLoad.url);
            memoryCache.put(photoToLoad.url, bmp);
            if (imageViewReused(photoToLoad))
                return;
            BitmapDisplayer bd = new BitmapDisplayer(bmp, photoToLoad);
            // 更新的操作放在UI线程中
            Activity a = (Activity) photoToLoad.imageView.getContext();
            a.runOnUiThread(bd);
        }
    }

    /**
     * 防止图片错位
     * 
     * @param photoToLoad
     * @return
     */
    boolean imageViewReused(PhotoToLoad photoToLoad) {
        String tag = imageViews.get(photoToLoad.imageView);
        if (tag == null || !tag.equals(photoToLoad.url))
            return true;
        return false;
    }

    // 用于在UI线程中更新界面
    class BitmapDisplayer implements Runnable {
        Bitmap bitmap;
        PhotoToLoad photoToLoad;

        public BitmapDisplayer(Bitmap b, PhotoToLoad p) {
            bitmap = b;
            photoToLoad = p;
        }

        public void run() {
            if (imageViewReused(photoToLoad))
                return;
            if (bitmap != null)
                photoToLoad.imageView.setImageBitmap(bitmap);
            else
                photoToLoad.imageView.setImageResource(stub_id);
        }
    }

    public void clearCache() {
        memoryCache.clear();
        fileCache.clear();
    }

    public static void CopyStream(InputStream is, OutputStream os) {
        final int buffer_size = 1024;
        try {
            byte[] bytes = new byte[buffer_size];
            for (;;) {
                int count = is.read(bytes, 0, buffer_size);
                if (count == -1)
                    break;
                os.write(bytes, 0, count);
            }
        } catch (Exception ex) {
        }
    }
}

主要流程是先从内存缓存中查找,若没有再开线程,从文件缓存中查找都没有则从指定的url中查找,并对bitmap进行处理,最后通过下面方法对UI进行更新操作。

a.runOnUiThread(...);

在你的程序中的基本用法:

ImageLoader imageLoader=new ImageLoader(context);
...
imageLoader.DisplayImage(url, imageView);
 比如你的放在你的ListView的adapter的getView()方法中,当然也适用于GridView。

wemall官网地址:http://www.wemallshop.com
原文详情地址:http://Git.oschina.NET/zzunet...
wemall doraemonAndroid app商城详情地址:http://www.koahub.com/home/pr...
wemall 开源微商城 ,微信商城,商城源码,三级分销,微生鲜,微水果,微外卖,微订餐---专业的o2o系统

wemall app商城源码Android之ListView异步加载网络图片(优化缓存机制)

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