LruCaChe缓存

把图片的加载利用LruCaChe进行缓存，无需每一次都请求网页图片，缓存可以有效的使APP节省流量。

1.创建LruCaChe缓存类

MyApplication/app/src/main/java/com/example/myapplication/ImageLoader.java

//创建Cache
private LruCache<String, Bitmap> mCaches;

public ImageLoader(){
    //构造方法
    //获取最大可用内存
    int  maxMemory = (int) Runtime.getRuntime().maxMemory();
    //缓存为内存的四分之一
    int cacheSize = maxMemory / 4;
    mCaches = new LruCache<String, Bitmap>(cacheSize){
        @Override
        protected int sizeOf(String key, Bitmap value) {
            //每次加入内存缓存的时候进行调用,把value的实际大小放进去
            return value.getByteCount();
        }
    };
}

2.增加缓存和读取缓存的方法

MyApplication/app/src/main/java/com/example/myapplication/ImageLoader.java

/**
 * 增加到缓存
 * @param url
 * @param bitmap
 */
public void addBitmapToCache(String url, Bitmap bitmap){
    //判断缓存中是否有这个值
    if(getBitmapFromCache(url) == null){
        mCaches.put(url, bitmap);
    }
}

/**
 * 从缓存中读取数据
 * @param url
 * @return
 */
public Bitmap getBitmapFromCache(String url){
    //获取缓存的对象
    return mCaches.get(url);
}

3.调用的方法和AsyncTask下载图片

MyApplication/app/src/main/java/com/example/myapplication/ImageLoader.java

/**
 * 根据url获取图片的Bitmap对象
 * @param urlString
 * @return
 */
public Bitmap getBitmapFromURL(String urlString){
    Bitmap bitmap;
    InputStream is = null;
    try {
        URL url = new URL(urlString);
        HttpsURLConnection connection = (HttpsURLConnection) url.openConnection();
        is = new BufferedInputStream(connection.getInputStream());
        bitmap = BitmapFactory.decodeStream(is);
        connection.disconnect();
        return bitmap;
    } catch (java.io.IOException e) {
        e.printStackTrace();
    } finally {
        try {
            is.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return null;
}

public void showImageByAsyncTask(ImageView imageView,String url){
    //判断缓存中是否有
    Bitmap bitmap = getBitmapFromCache(url);
    if(bitmap == null){
        //缓存中没有就去下载
        new NewsAsyncTask(imageView, url).execute(url);
    }else{
        imageView.setImageBitmap(bitmap);
    }

}

/**
 * AsyncTask的方式把图片放入view
 */
private class NewsAsyncTask extends AsyncTask<String, Void, Bitmap>{

    private ImageView mImageView;
    private String murl;

    public NewsAsyncTask(ImageView imageView, String url){
        mImageView = imageView;
        murl = url;
    }

    @Override
    protected Bitmap doInBackground(String... strings) {
        String url = strings[0];
        //从网络中获取图片
        Bitmap bitmap = getBitmapFromURL(url);
        if(bitmap != null){
            //增加到缓存
            addBitmapToCache(url, bitmap);
        }
        return bitmap;
    }

    @Override
    protected void onPostExecute(Bitmap bitmap) {
        super.onPostExecute(bitmap);
        //防止图片重复判断唯一性
        if(mImageView.getTag().equals(murl)) {
            mImageView.setImageBitmap(bitmap);
        }
    }
}

4.NewsAdapter调用方法

MyApplication/app/src/main/java/com/example/myapplication/NewsAdapter.java

private ImageLoader mImageLoader;
public NewsAdapter(Context context, List<NewBean> data){
    //构造方法
    mImageLoader = new ImageLoader();
}

//调用如下：
mImageLoader.showImageByAsyncTask(viewHolder.newPic, mList.get(position).getPicUrl());