android BitmapFactory的OutOfMemoryError: bitmap ...

網上有不少解決android加載bitmap內存溢出的方法，搜了一圈作下整理總結。項目裏需求是拍攝多圖以後上傳，部分手機會內存溢出。

經常使用一種解決方法：即將載入的圖片縮小，這種方式以犧牲圖片的質量爲代價。在BitmapFactory中有一個內部類BitmapFactory.Options，其中當options.inSampleSize值>1時，根據文檔：

If set to a value > 1, requests the decoder to subsample the original image, returning a smaller image to save memory. (1 -> decodes full size; 2 -> decodes 1/4th size; 4 -> decode 1/16th size). Because you rarely need to show and have full size bitmap images on your phone. For manipulations smaller sizes are usually enough.
options.inSampleSize是以2的指數的倒數被進行放縮

如今問題是怎麼肯定inSampleSize的值？每張圖片的放縮大小的比例應該是不同的！這樣的話就要運行時動態肯定。在BitmapFactory.Options中提供了另外一個成員inJustDecodeBounds。
設置inJustDecodeBounds爲true後，decodeFile並不分配空間，但可計算出原始圖片的長度和寬度，即opts.width和opts.height。有了這兩個參數，再經過必定的算法，便可獲得一個恰當的inSampleSize。Android提供了一種動態計算的方法，見computeSampleSize().

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

以上只作爲參考，咱們只要用這函數便可，opts.inSampleSize = computeSampleSize(opts, -1, 128*128);




要點：
一、用decodeFileDescriptor()來生成bimap比decodeFile()省內存

FileInputStream is = = new FileInputStream(path);
bmp = BitmapFactory.decodeFileDescriptor(is.getFD(), null, opts);

替換

Bitmap bmp = BitmapFactory.decodeFile(imageFile, opts);
    imageView.setImageBitmap(bmp);

 

緣由：
查看BitmapFactory的源碼，對比一下二者的實現，能夠發現decodeFile()最終是以流的方式生成bitmap 

decodeFile源碼：

public static Bitmap decodeFile(String pathName, Options opts) {
        Bitmap bm = null;
        InputStream stream = null;
        try {
            stream = new FileInputStream(pathName);
            bm = decodeStream(stream, null, opts);
        } catch (Exception e) {
            /*  do nothing.
                If the exception happened on open, bm will be null.
            */
        } finally {
            if (stream != null) {
                try {
                    stream.close();
                } catch (IOException e) {
                    // do nothing here
                }
            }
        }
        return bm;
    }

 

decodeFileDescriptor的源碼，能夠找到native本地方法decodeFileDescriptor，經過底層生成bitmap

decodeFileDescriptor源碼：

public static Bitmap decodeFileDescriptor(FileDescriptor fd, Rect outPadding, Options opts) {
        if (nativeIsSeekable(fd)) {
            Bitmap bm = nativeDecodeFileDescriptor(fd, outPadding, opts);
            if (bm == null && opts != null && opts.inBitmap != null) {
                throw new IllegalArgumentException("Problem decoding into existing bitmap");
            }
            return finishDecode(bm, outPadding, opts);
        } else {
            FileInputStream fis = new FileInputStream(fd);
            try {
                return decodeStream(fis, outPadding, opts);
            } finally {
                try {
                    fis.close();
                } catch (Throwable t) {/* ignore */}
            }
        }
    }

 private static native Bitmap nativeDecodeFileDescriptor(FileDescriptor fd,Rect padding, Options opts);

二、當在android設備中載入較大圖片資源時，能夠建立一些臨時空間，將載入的資源載入到臨時空間中。

opts.inTempStorage = new byte[16 * 1024];

?

 

 

完整代碼：

public static OutputStream decodeBitmap(String path) {

		BitmapFactory.Options opts = new BitmapFactory.Options();
		opts.inJustDecodeBounds = true;// 設置成了true,不佔用內存，只獲取bitmap寬高
		BitmapFactory.decodeFile(path, opts);
		opts.inSampleSize = computeSampleSize(opts, -1, 1024 * 800);

		opts.inJustDecodeBounds = false;// 這裏必定要將其設置回false，由於以前咱們將其設置成了true
		opts.inPurgeable = true;
		opts.inInputShareable = true;
		opts.inDither = false;
		opts.inPurgeable = true;
		opts.inTempStorage = new byte[16 * 1024];
		FileInputStream is = null;
		Bitmap bmp = null;
		InputStream ins = null;
		ByteArrayOutputStream baos = null;
		try {
			is = new FileInputStream(path);
			bmp = BitmapFactory.decodeFileDescriptor(is.getFD(), null, opts); 			double scale = getScaling(opts.outWidth * opts.outHeight, 1024 * 600);
			Bitmap bmp2 = Bitmap.createScaledBitmap(bmp,
					(int) (opts.outWidth * scale),
					(int) (opts.outHeight * scale), true);
			bmp.recycle();
			baos = new ByteArrayOutputStream();
			bmp2.compress(Bitmap.CompressFormat.JPEG, 100, baos);
			bmp2.recycle();
			return baos;
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				is.close();
				ins.close();
				baos.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
			System.gc();
		}
		return baos;
	}

private static double getScaling(int src, int des) {
/**
 * 目標尺寸÷原尺寸 sqrt開方，得出寬高百分比
 */
    double scale = Math.sqrt((double) des / (double) src);
    return scale;
}