彻底解决Android因加载多个大图引起的OutOfMemoryError，内存溢出的问题

最近因为项目里需求是选择或者拍摄多张照片后，提供滑动预览和上传，很多照片是好几MB一张，因为目前的Android系统对运行的程序都有一定的内存限制，一般是16MB或24MB(视平台而定)，不做处理直接加载的话必然会报OOM (Out Of Memmory)。网上有很多解决android加载bitmap内存溢出的方法，我总结了一个通用的方法，下面是我从的开发案例抽取出来的代码：

我在项目中建了个Util.java工具类，里面写了个方法，根据图片的路径返回一个字节流数组对象：

public static byte[] decodeBitmap(String path) {
		BitmapFactory.Options opts = new BitmapFactory.Options();
		opts.inJustDecodeBounds = true;// 设置成了true,不占用内存，只获取bitmap宽高
		BitmapFactory.decodeFile(path, opts);
		opts.inSampleSize = computeSampleSize(opts, -1, 1024 * 800);
		opts.inJustDecodeBounds = false;// 这里一定要将其设置回false，因为之前我们将其设置成了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;
		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.toByteArray();
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				is.close();
				baos.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
			System.gc();
		}
		return baos.toByteArray();
	}

	private static double getScaling(int src, int des) {
		/**
		 * 48 目标尺寸÷原尺寸 sqrt开方，得出宽高百分比 49
		 */
		double scale = Math.sqrt((double) des / (double) src);
		return scale;
	}

	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;
		}
	}

然后在我需要加载图片BitMap的地方来调用Util.decodeBitmap():

Bitmap bitmap = BitmapFactory.decodeByteArray(Util.decodeBitmap(imagePath), 0, Util.decodeBitmap(imagePath).length);
                imageCache.put(imagePath, new SoftReference<Bitmap>(bitmap));

上面这两行是我的AsyncImageLoaderByPath类中的代码，用来加载SD卡里面的图片，该类完整代码是：

package com.pioneer.travel.util;

import java.io.IOException;
import java.io.InputStream;
import java.lang.ref.SoftReference;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapFactory.Options;
import android.graphics.drawable.Drawable;
import android.os.Handler;
import android.os.Message;
import android.provider.MediaStore;
import android.util.Log;
import android.widget.ImageView;

public class AsyncImageLoaderByPath {
    //SoftReference是软引用，是为了更好的为了系统回收变量
    private HashMap<String, SoftReference<Bitmap>> imageCache;
    private Context context;

    public AsyncImageLoaderByPath(Context context) {
        this.imageCache = new HashMap<String, SoftReference<Bitmap>>();
        this.context = context;
    }
    public Bitmap loadBitmapByPath(final String imagePath, final ImageView imageView, final ImageCallback imageCallback){
        if (imageCache.containsKey(imagePath)) {
            //从缓存中获取
            SoftReference<Bitmap> softReference = imageCache.get(imagePath);
            Bitmap bitmap = softReference.get();
            if (bitmap != null) {
                return bitmap;
            }
        }
        final Handler handler = new Handler() {
            public void handleMessage(Message message) {
                imageCallback.imageLoaded((Bitmap) message.obj, imageView, imagePath);
            }
        };
        //建立新一个获取SD卡的图片
        new Thread() {
            @Override
            public void run() {
            	Bitmap bitmap = BitmapFactory.decodeByteArray(Util.decodeBitmap(imagePath), 0, Util.decodeBitmap(imagePath).length);
                imageCache.put(imagePath, new SoftReference<Bitmap>(bitmap));
                Message message = handler.obtainMessage(0, bitmap);
                handler.sendMessage(message);
            }
        }.start();
        return null;
    }
    //回调接口
    public interface ImageCallback {
        public void imageLoaded(Bitmap imageBitmap,ImageView imageView, String imagePath);
    }
}

通过这个实例，我验证了一下，一次性获取20张5MB的照片，都可以加载的很流畅，完全没有再出现报OOM的错误了

以下是运行效果

SD卡中的图片：

进入应用，选择11张照片进行滑动预览：

希望以上所写对大家有帮助，谢谢！