Android Bitmap那些事之如何优化内存

BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds =true;
BitmapFactory.decodeResource(getResources(), R.id.myimage, options);
int imageHeight = options.outHeight;
int imageWidth = options.outWidth;
String imageType = options.outMimeType;

public static int calculateInSampleSize(
            BitmapFactory.Options options,int reqWidth,int reqHeight){
    // Raw height and width of image
    finalint height = options.outHeight;
    finalint width = options.outWidth;
    int inSampleSize =1;

    if(height > reqHeight || width > reqWidth){

        finalint halfHeight = height /2;
        finalint halfWidth = width /2;

        // Calculate the largest inSampleSize value that is a power of 2 and keeps both
        // height and width larger than the requested height and width.
        while((halfHeight / inSampleSize)> reqHeight
                &&(halfWidth / inSampleSize)> reqWidth){
            inSampleSize *=2;
        }
    }

    return inSampleSize;
}

public static Bitmap decodeSampledBitmapFromResource(Resources res,int resId,
        int reqWidth,int reqHeight){

    // First decode with inJustDecodeBounds=true to check dimensions
    finalBitmapFactory.Options options =newBitmapFactory.Options();
    options.inJustDecodeBounds =true;
    BitmapFactory.decodeResource(res, resId, options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds =false;
    returnBitmapFactory.decodeResource(res, resId, options);
}

    /**
     * 对图片进行压缩，主要是为了解决控件显示过大图片占用内存造成OOM问题,一般压缩后的图片大小应该和用来展示它的控件大小相近.
     *
     * @param context 上下文
     * @param resId 图片资源Id
     * @param reqWidth 期望压缩的宽度
     * @param reqHeight 期望压缩的高度
     * @return 压缩后的图片
     */
    public static Bitmap compressBitmapFromResourse(Context context, int resId, int reqWidth, int reqHeight) {
        final BitmapFactory.Options options = new BitmapFactory.Options();
        /*
         * 第一次解析时，inJustDecodeBounds设置为true，
         * 禁止为bitmap分配内存，虽然bitmap返回值为空，但可以获取图片大小
         */
        options.inJustDecodeBounds = true;
        BitmapFactory.decodeResource(context.getResources(), resId, options);

        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;
        if (height > reqHeight || width > reqWidth) {
            final int heightRatio = Math.round((float) height / (float) reqHeight);
            final int widthRatio = Math.round((float) width / (float) reqWidth);
            inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
        }
        options.inSampleSize = inSampleSize;
        // 使用计算得到的inSampleSize值再次解析图片
        options.inJustDecodeBounds = false;
        return BitmapFactory.decodeResource(context.getResources(), resId, options);
    }