【转】解决Android因加载多个大图引起的OutOfMemoryError，内存溢出的问题

本文来自：http://blog.csdn.net/wulianghuan/article/details/11548373，感谢原作者的分享。

目标是读取SD卡中的图片并且展示出来

主要思路是通过一个工具类来压缩来自sd卡中的图片，最后通过缓存机制来避免占用过多内存。

Util.java

package com.kale.socketactivity;

import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

public class Util {
    
    /**
     * @param path
     * @return
     * @example Bitmap bitmap = BitmapFactory.decodeByteArray(Util.decodeBitmap(imagePath), 0, Util.decodeBitmap(imagePath).length);  
                imageCache.put(imagePath, new SoftReference<Bitmap>(bitmap));  //这里用了软引用
     */
    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);
            //从文件中读取图片，可以换为别的方式
            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;
        }
    }
}

使用方式：

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

实现类

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);
    }
}