首页 › Android开发 › android 用LruCache读取大图片并缓存(转)

志强思密达 发表于 2013-1-3 17:00:51

android 用LruCache读取大图片并缓存(转)

<div id="cnblogs_post_body">图片预取缓存策略是内存缓存（硬引用LruCache、软引用SoftReference<Bitmap>）、外部文件缓存（context.getCachedDir()），缓存中取不到的情况下再向服务端请求下载图片。同时缓存三张图片（当前预览的这张，前一张以及后一张）。
1.内存缓存

<div class="cnblogs_code">•//需要导入外部jar文件 android-support-v4.jar •import android.support.v4.util.LruCache; •//开辟8M硬缓存空间 •private final int hardCachedSize = 8*1024*1024; •//hard cache •private final LruCache<String, Bitmap> sHardBitmapCache = new LruCache<String, Bitmap>(hardCachedSize){ •@Override •public int sizeOf(String key, Bitmap value){ •return value.getRowBytes() * value.getHeight(); •} •@Override •protected void entryRemoved(boolean evicted, String key, Bitmap oldValue, Bitmap newValue){ •Log.v("tag", "hard cache is full , push to soft cache"); •//硬引用缓存区满，将一个最不经常使用的oldvalue推入到软引用缓存区 •sSoftBitmapCahe.put(key, new SoftReference<Bitmap>(oldValue)); •} •} •//软引用 •private static final int SOFT_CACHE_CAPACITY = 40; •private final static LinkedHashMap<String, SoftReference<Bitmap>> sSoftBitmapCache = •new LinkedHashMao<String, SoftReference<Bitmap>>(SOFT_CACHE_CAPACITY, 0.75f, true){ •@Override •public SoftReference<Bitmap> put(String key, SoftReference<Bitmap> value){ •return super.input(key, value); •} •@Override •protected boolean removeEldestEntry(LinkedHashMap.Entry<Stirng, SoftReference<Bitmap>> eldest){ •if(size() > SOFT_CACHE_CAPACITY){ •Log.v("tag", "Soft Reference limit , purge one"); •return true; •} •return false; •} •} •//缓存bitmap •public boolean putBitmap(String key, Bitmap bitmap){ •if(bitmap != null){ •synchronized(sHardBitmapCache){ •sHardBitmapCache.put(key, bitmap); •} •return true; •} •return false; •} •//从缓存中获取bitmap •public Bitmap getBitmap(String key){ •synchronized(sHardBitmapCache){ •final Bitmap bitmap = sHardBitmapCache.get(key); •if(bitmap != null) •return bitmap; •} •//硬引用缓存区间中读取失败，从软引用缓存区间读取 •synchronized(sSoftBitmapCache){ •SoftReference<Bitmap> bitmapReference = sSoftBtimapCache.get(key); •if(bitmapReference != null){ •final Bitmap bitmap2 = bitmapReference.get(); •if(bitmap2 != null) •return bitmap2; •else{ •Log.v("tag", "soft reference 已经被回收"); •sSoftBitmapCache.remove(key); •} •} •} •return null; •}

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