昨天写了关于BitMap关于图片压缩的博客， 今天写一下关于图片的内存缓存 。这些文章网上很多，与其每次找别人的博客，还不如自己写一篇 。加深记忆
都是一些比较老的技术了，没什么好解释的 ，看看就懂了 。
还是来一张妹子镇楼
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图片缓存类
public class LruCacheUtil { Context context; LruCache<String, Bitmap> mMemoryCache; public static final String TAG = "LruCacheUtil"; public LruCacheUtil(Context context) { this.context = context.getApplicationContext(); int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024); //获取手机的最大内存 int cacheSize = maxMemory / 8; //使用内存的1/8用来做图片缓存 mMemoryCache = new LruCache<String, Bitmap>(cacheSize) { @Override protected int sizeOf(String key, Bitmap bitmap) { return bitmap.getRowBytes() * bitmap.getHeight() / 1024; } }; } /*** * 清理缓存 */ public void clearCache() { if (mMemoryCache != null) { if (mMemoryCache.size() > 0) { Log.d(TAG, "mMemoryCache.size() " + mMemoryCache.size()); mMemoryCache.evictAll(); Log.d(TAG, "mMemoryCache.size()" + mMemoryCache.size()); } mMemoryCache = null; } } /*** * 添加图片到缓存 * @param key * @param bitmap */ public synchronized void addBitmapToMemoryCache(String key, Bitmap bitmap) { if (mMemoryCache.get(key) == null) { if (key != null && bitmap != null) mMemoryCache.put(key, bitmap); Log.w(TAG, "添加图片到缓存"); } else Log.w(TAG, "图片缓存已经存在"); } /*** * 从缓存中去拿图片 * @param key * @return */ public synchronized Bitmap getBitmapFromMemCache(String key) { try { Bitmap bm = mMemoryCache.get(key); if (key != null) { return bm; } } catch (Exception e) { return null; } return null; } /** * 移除缓存 * * @param key */ public synchronized void removeImageCache(String key) { if (key != null) { if (mMemoryCache != null) { Bitmap bm = mMemoryCache.remove(key); if (bm != null) bm.recycle(); } } } }//==============================================
图片压缩类，上一章节也讲过
public class ImageResizer { public ImageResizer() { } /*** * 从资源文件中读取图片资源 * @param resources * @param resId * @param reqWidth * @param reqHeight * @return */ public Bitmap decodeSampleBitmapFactoryFromResource(Resources resources, int resId, int reqWidth, int reqHeight) { BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; //去加载图片 BitmapFactory.decodeResource(resources, resId, options); options.inSampleSize = calculateImSampleSize(options, reqWidth, reqHeight); options.inJustDecodeBounds = false; return BitmapFactory.decodeResource(resources, resId, options); } public Bitmap decodeBitmapFromFileDescriptor(FileDescriptor fd, int reqWidth, int reqheight) { BitmapFactory.Options options = new BitmapFactory.Options(); options.inJustDecodeBounds = true; BitmapFactory.decodeFileDescriptor(fd, null, options); options.inSampleSize = calculateImSampleSize(options, reqWidth, reqheight); options.inJustDecodeBounds = false; return BitmapFactory.decodeFileDescriptor(fd, null, options); } /*** * 计算图片的压缩比例 * @param options * @param reqWidth * @param reqHeight * @return */ private int calculateImSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) { if (reqHeight == 0 || reqWidth == 0) { return 1; } int height = options.outHeight; int width = options.outWidth; int inSampleSize = 1; if (height > reqHeight || reqWidth > reqWidth) { int halfWidth = width / 2; int halfHeight = height / 2; while ((halfHeight / inSampleSize) >= reqHeight || (halfWidth / inSampleSize) >= reqWidth) { inSampleSize *= 2; } } return inSampleSize; }======================================================
主界面的调用类 ，用了清理缓存 ，延迟两秒，大家有兴趣可以自己看下效果，
public class MainActivity extends AppCompatActivity { private ImageView iv_image; LruCacheUtil lruCacheUtil; private Handler handler = new Handler(); ImageResizer mImageResizer; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); intView(); } private void intView() { mImageResizer = new ImageResizer(); lruCacheUtil = new LruCacheUtil(MainActivity.this); Bitmap map = mImageResizer.decodeSampleBitmapFactoryFromResource(getResources(), R.mipmap.aa, 500, 500); lruCacheUtil.addBitmapToMemoryCache("123456", map); iv_image = (ImageView) findViewById(R.id.iv_image); Bitmap mapShow = lruCacheUtil.getBitmapFromMemCache("123456"); iv_image.setImageBitmap(mapShow); handler.postDelayed(new Runnable() { @Override public void run() { lruCacheUtil.clearCache(); Bitmap mapShow = lruCacheUtil.getBitmapFromMemCache("123456"); iv_image.setImageBitmap(mapShow); } }, 2000); } }
