Android使用BitmapFactory.Options压缩图片解决加载大图片内存溢出

由于Android对图片使用内存有限制，若是加载几兆的大图片便内存溢出。Bitmap会将图片的所有像素（即长x宽）加载到内存中，如果图片分辨率过大，会直接导致内存溢出（java.lang.OutOfMemoryError），只有在BitmapFactory加载图片时使用BitmapFactory.Options对相关参数进行配置来减少加载的像素。

1、设置缩放大小对图片作处理

public Bitmap getBitmapFromFile(File dst, int width, int height) {
    if (null != dst && dst.exists()) {
        BitmapFactory.Options opts = null;
        if (width > 0 && height > 0) {
            opts = new BitmapFactory.Options();
            opts.inJustDecodeBounds = true;
            BitmapFactory.decodeFile(dst.getPath(), opts);
            // 计算图片缩放比例
            final int minSideLength = Math.min(width, height);
            opts.inSampleSize = computeSampleSize(opts, minSideLength,
                    width * height);
            opts.inJustDecodeBounds = false;
            opts.inInputShareable = true;
            opts.inPurgeable = true;
        }
        try {
            return BitmapFactory.decodeFile(dst.getPath(), opts);
        } catch (OutOfMemoryError e) {
            e.printStackTrace();
        }
    }
    return null;
}

public static int computeSampleSize(BitmapFactory.Options options,
        int minSideLength, int maxNumOfPixels) {
    int initialSize = computeInitialSampleSize(options, minSideLength,
            maxNumOfPixels);

    int roundedSize;
    if (initialSize <= 8) {
        roundedSize = 1;
        while (roundedSize < initialSize) {
            roundedSize <<= 1;
        }
    } else {
        roundedSize = (initialSize + 7) / 8 * 8;
    }

    return roundedSize;
}

private static int computeInitialSampleSize(BitmapFactory.Options options,
        int minSideLength, int maxNumOfPixels) {
    double w = options.outWidth;
    double h = options.outHeight;

    int lowerBound = (maxNumOfPixels == -1) ? 1 : (int) Math.ceil(Math
            .sqrt(w * h / maxNumOfPixels));
    int upperBound = (minSideLength == -1) ? 128 : (int) Math.min(Math
            .floor(w / minSideLength), Math.floor(h / minSideLength));

    if (upperBound < lowerBound) {
        // return the larger one when there is no overlapping zone.
        return lowerBound;
    }

    if ((maxNumOfPixels == -1) && (minSideLength == -1)) {
        return 1;
    } else if (minSideLength == -1) {
        return lowerBound;
    } else {
        return upperBound;
    }
}

	/**
	 * 获取经过处理的资源图，包括普通图和.9图
	 * @param context 应用环境
	 * @param id 资源id
	 * @return Drawable格式的资源
	 * <p>
	 * 以1080p为基准，小于此尺寸的缩写，大于此尺寸的放大
	 */
	public static Drawable getCompatibleDrawable(Context context, int id) {
		BitmapFactory.Options options = new BitmapFactory.Options();
		options.inDensity = 240;
		options.inScreenDensity = (int) (240*ratio);
		options.inTargetDensity = (int) (240*ratio);

		Bitmap bitmap = BitmapFactory.decodeResource(context.getResources(),
				id, options);
		byte[] ninePathChunk = bitmap.getNinePatchChunk();
		
		if (NinePatch.isNinePatchChunk(ninePathChunk)) {
			NinePatch ninePath = new NinePatch(bitmap, ninePathChunk, null);
			
			return new NinePatchDrawable(ninePath);
		} else {
			return new BitmapDrawable(bitmap);
		}
	}