仿微信图片选择器 imageloader源码-原创手记-慕课网

package com.example.com.imageloader;

import android.annotation.TargetApi;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Build;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.util.DisplayMetrics;
import android.util.LruCache;
import android.view.ViewGroup;
import android.widget.ImageView;

import java.util.LinkedList;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;

/**

Created by 61678 on 2016/6/29.
*/
public class ImageLoader {
private static ImageLoader imageLoader;
/**
- 图片缓存核心
  */
  private LruCache<String, Bitmap> mLrucache;
  /**
- 线程池
  */
  private ExecutorService mThreadPool;
  private static final int DEFAULT_THREAD_COUNT = 1;
/**
- 队列调度模式
  */
  private Type type = Type.LIFO;
  /**
- 任务队列
  */
  LinkedList<Runnable> mTAskQueue;
  /**
- 后台轮询线程
  */
  Thread mPoolThread;
  Handler mPoolThreadHandler;
Handler mUIHandler;

Semaphore semaphore = new Semaphore(0);
Semaphore semaphoreHandler;

private enum Type {
LIFO, FIFO;
}

public void loadImage(final String path, final ImageView imageView) {
imageView.setTag(path);
if (mUIHandler == null) {
mUIHandler = new Handler(Looper.getMainLooper()) {
@Override
public void handleMessage(Message msg) {
//获取图片，为imageview设置图片
ImgBeanHold imgBeanHold = (ImgBeanHold) msg.obj;
Bitmap bitmap = imgBeanHold.bitmap;
String path = imgBeanHold.path;
ImageView imageView = imgBeanHold.imageView;
```
            if (imageView.getTag().toString().equals(path)) {
                imageView.setImageBitmap(bitmap);
            }
        }
    };
}
Bitmap bitmap = getBitmapFromCache(path);

if (bitmap != null) {
    refresh(path, imageView, bitmap);
} else {
    addTast(new Runnable() {
        @Override
        public void run() {
            ImgSize size = getImgSize(imageView);
            Bitmap bm = decodeBitmap(path, size.width, size.hei);

            addLruCache(path, bm);

            refresh(path, imageView, bm);

            semaphoreHandler.release();
        }
    });
}
```
}

private void refresh(String path, ImageView imageView, Bitmap bitmap) {
Message message = Message.obtain();
ImgBeanHold imgBeanHold = new ImgBeanHold();
imgBeanHold.bitmap = bitmap;
imgBeanHold.path = path;
imgBeanHold.imageView = imageView;
message.obj = imgBeanHold;
mUIHandler.sendMessage(message);
}

private synchronized void addLruCache(String path, Bitmap bm) {
if (getBitmapFromCache(path) == null) {
if (bm != null) {
mLrucache.put(path, bm);
}
}
}

private Bitmap decodeBitmap(String path, int width, int hei) {
BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(path, options);
```
options.inSampleSize = caculateSampleSize(options, width, hei);

options.inJustDecodeBounds = false;

return BitmapFactory.decodeFile(path, options);
```
}

private int caculateSampleSize(BitmapFactory.Options options, int Rwidth, int Rhei) {
int wid = options.outWidth;
int hei = options.outHeight;
```
int sampleSize = 1;
if (wid > Rwidth  hei > Rhei) {

    sampleSize = Math.max(Math.round(wid * 1.0f / Rwidth),
            Math.round(hei * 1.0f / Rhei));
}

return sampleSize;
```
}

@TargetApi(Build.VERSION_CODES.JELLY_BEAN)
private ImgSize getImgSize(ImageView imageView) {
ImgSize size = new ImgSize();
DisplayMetrics metrics = imageView.getContext().getResources().getDisplayMetrics();
```
ViewGroup.LayoutParams params = imageView.getLayoutParams();
int width = imageView.getWidth();

if (width <= 0) {
    width = params.width;
}
if (width <= 0) {
    width = imageView.getMaxWidth();
}
if (width <= 0) {
    width = metrics.widthPixels;
}

int hei = imageView.getHeight();
if (hei <= 0) {
    hei = params.height;
}
if (hei <= 0) {
    hei = imageView.getMaxHeight();
}
if (hei <= 0) {
    hei = metrics.heightPixels;
}

size.hei = hei;
size.width = width;

return size;
```
}

private class ImgSize {
int hei;
int width;
}

private void addTast(Runnable runnable) {
mTAskQueue.add(runnable);
if (mPoolThreadHandler == null) {
try {
semaphore.acquire();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
mPoolThreadHandler.sendEmptyMessage(1);
}

private class ImgBeanHold {
Bitmap bitmap;
String path;
ImageView imageView;
}

private Bitmap getBitmapFromCache(String path) {
```
return mLrucache.get(path);
```
}

private ImageLoader(int mThreadCount, Type type) {
```
init(mThreadCount, type);
```
}

private Runnable getTask() {
if (type == Type.LIFO) {
return mTAskQueue.removeLast();
}
if (type == Type.FIFO) {
return mTAskQueue.removeFirst();
}
return null;
}

private void init(int mThreadCount, Type type) {
mPoolThread = new Thread() {
@Override
public void run() {
Looper.prepare();
mPoolThreadHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
//线程池取出一个任务执行
```
                mThreadPool.execute(getTask());
                try {
                    semaphoreHandler.acquire();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        semaphore.release();
        Looper.loop();
    }
};
mPoolThread.start();

int maxMemory = (int) Runtime.getRuntime().maxMemory();
int cacheMemory = maxMemory / 8;
mLrucache = new LruCache<String, Bitmap>(cacheMemory) {
    @Override
    protected int sizeOf(String key, Bitmap value) {
        return value.getRowBytes() * value.getHeight();
    }
};
//创建线程池
mThreadPool = Executors.newFixedThreadPool(mThreadCount);
mTAskQueue = new LinkedList<>();
this.type = type;
semaphoreHandler = new Semaphore(mThreadCount);
```
}

public static ImageLoader getImageLoader() {
if (imageLoader == null) {
synchronized (ImageLoader.class) {
if (imageLoader == null) {
imageLoader = new ImageLoader(DEFAULT_THREAD_COUNT, Type.LIFO);
}
}
}
return imageLoader;
}
}