android本地图片加载器,LruCache缓存机制

package com.dingmore.mobile.ui.picselect;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.Point;import android.os.Handler;import android.os.Message;import android.support.v4.util.LruCache;/** * 本地图片加载器,采用的是异步解析本地图片，单例模式利用getInstance()获取NativeImageLoader实例 * 调用loadNativeImage()方法加载本地图片，此类可作为一个加载本地图片的工具类 *  * */public class NativeImageLoader {private LruCache<String, Bitmap> mMemoryCache;private static NativeImageLoader mInstance = new NativeImageLoader();private ExecutorService mImageThreadPool = Executors.newFixedThreadPool(1);private NativeImageLoader(){//获取应用程序的最大内存final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);//用最大内存的1/4来存储图片final int cacheSize = maxMemory / 4;mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {//获取每张图片的大小@Overrideprotected int sizeOf(String key, Bitmap bitmap) {return bitmap.getRowBytes() * bitmap.getHeight() / 1024;}};}/** * 通过此方法来获取NativeImageLoader的实例 * @return */public static NativeImageLoader getInstance(){return mInstance;}/** * 加载本地图片，对图片不进行裁剪 * @param path * @param mCallBack * @return */public Bitmap loadNativeImage(final String path, final NativeImageCallBack mCallBack){return this.loadNativeImage(path, null, mCallBack);}/** * 此方法来加载本地图片，这里的mPoint是用来封装ImageView的宽和高，我们会根据ImageView控件的大小来裁剪Bitmap * 如果你不想裁剪图片，调用loadNativeImage(final String path, final NativeImageCallBack mCallBack)来加载 * @param path * @param mPoint * @param mCallBack * @return */public Bitmap loadNativeImage(final String path, final Point mPoint, final NativeImageCallBack mCallBack){//先获取内存中的BitmapBitmap bitmap = getBitmapFromMemCache(path);final Handler mHander = new Handler(){@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);mCallBack.onImageLoader((Bitmap)msg.obj, path);}};//若该Bitmap不在内存缓存中，则启用线程去加载本地的图片，并将Bitmap加入到mMemoryCache中if(bitmap == null){mImageThreadPool.execute(new Runnable() {@Overridepublic void run() {//先获取图片的缩略图Bitmap mBitmap = decodeThumbBitmapForFile(path, mPoint == null ? 0: mPoint.x, mPoint == null ? 0: mPoint.y);Message msg = mHander.obtainMessage();msg.obj = mBitmap;mHander.sendMessage(msg);//将图片加入到内存缓存addBitmapToMemoryCache(path, mBitmap);}});}return bitmap;}/** * 往内存缓存中添加Bitmap *  * @param key * @param bitmap */private void addBitmapToMemoryCache(String key, Bitmap bitmap) {if (getBitmapFromMemCache(key) == null && bitmap != null) {mMemoryCache.put(key, bitmap);}}/** * 根据key来获取内存中的图片 * @param key * @return */private Bitmap getBitmapFromMemCache(String key) {return mMemoryCache.get(key);}/** * 根据View(主要是ImageView)的宽和高来获取图片的缩略图 * @param path * @param viewWidth * @param viewHeight * @return */private Bitmap decodeThumbBitmapForFile(String path, int viewWidth, int viewHeight){BitmapFactory.Options options = new BitmapFactory.Options();//设置为true,表示解析Bitmap对象，该对象不占内存options.inJustDecodeBounds = true;BitmapFactory.decodeFile(path, options);//设置缩放比例options.inSampleSize = computeScale(options, viewWidth, viewHeight);//设置为false,解析Bitmap对象加入到内存中options.inJustDecodeBounds = false;return BitmapFactory.decodeFile(path, options);}/** * 根据View(主要是ImageView)的宽和高来计算Bitmap缩放比例。默认不缩放 * @param options * @param width * @param height */private int computeScale(BitmapFactory.Options options, int viewWidth, int viewHeight){int inSampleSize = 1;if(viewWidth == 0 || viewWidth == 0){return inSampleSize;}int bitmapWidth = options.outWidth;int bitmapHeight = options.outHeight;//假如Bitmap的宽度或高度大于我们设定图片的View的宽高，则计算缩放比例if(bitmapWidth > viewWidth || bitmapHeight > viewWidth){int widthScale = Math.round((float) bitmapWidth / (float) viewWidth);int heightScale = Math.round((float) bitmapHeight / (float) viewWidth);//为了保证图片不缩放变形，我们取宽高比例最小的那个inSampleSize = widthScale < heightScale ? widthScale : heightScale;}return inSampleSize;}/** * 加载本地图片的回调接口 *  * @author xiaanming * */public interface NativeImageCallBack{/** * 当子线程加载完了本地的图片，将Bitmap和图片路径回调在此方法中 * @param bitmap * @param path */public void onImageLoader(Bitmap bitmap, String path);}}