Bitmap_图片内存缓存（2）

来源：互联网发布：inpho软件编辑：程序博客网时间：2024/05/21 08:01

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();            }        }    }}

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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;    }

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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);    }}

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