VideoThumbLoader.java

package ml.puredark.hviewer.helpers;

import android.annotation.SuppressLint;
import android.graphics.Bitmap;
import android.media.ThumbnailUtils;
import android.os.AsyncTask;
import android.provider.MediaStore;
import android.support.v4.util.LruCache;
import android.widget.ImageView;

public class VideoThumbLoader {
    private volatile static VideoThumbLoader instance;
    //创建cache
    private LruCache<String, Bitmap> lruCache;

    @SuppressLint("NewApi")
    public VideoThumbLoader() {
        int maxMemory = (int) Runtime.getRuntime().maxMemory();//获取最大的运行内存
        int maxSize = maxMemory / 4;//拿到缓存的内存大小 35
        lruCache = new LruCache<String, Bitmap>(maxSize) {
            @Override
            protected int sizeOf(String key, Bitmap value) {
                //这个方法会在每次存入缓存的时候调用
                return value.getByteCount();
            }
        };
    }

    /**
     * Returns singleton class instance
     */
    public static VideoThumbLoader getInstance() {
        if (instance == null) {
            synchronized (VideoThumbLoader.class) {
                if (instance == null) {
                    instance = new VideoThumbLoader();
                }
            }
        }
        return instance;
    }

    public void addVideoThumbToCache(String path, Bitmap bitmap) {
        if (getVideoThumbToCache(path) == null) {
            //当前地址没有缓存时，就添加
            lruCache.put(path, bitmap);
        }
    }

    public Bitmap getVideoThumbToCache(String path) {

        return lruCache.get(path);

    }

    public void showThumbByAsynctack(ImageView imgview, String path) {
        if (imgview == null || path == null) return;
        if (getVideoThumbToCache(path) == null) {
            imgview.setTag(path);
            //异步加载
            new MyBobAsynctack(imgview, path).execute(path);
        } else {
            imgview.setImageBitmap(getVideoThumbToCache(path));
        }

    }

    class MyBobAsynctack extends AsyncTask<String, Void, Bitmap> {
        private ImageView imgView;
        private String path;

        public MyBobAsynctack(ImageView imageView, String path) {
            this.imgView = imageView;
            this.path = path;
        }

        @Override
        protected Bitmap doInBackground(String... params) {
            //这里的创建缩略图方法是调用VideoUtil类的方法，也是通过 android中提供的 ThumbnailUtils.createVideoThumbnail(vidioPath, kind);

            Bitmap bitmap = ThumbnailUtils.createVideoThumbnail(params[0], MediaStore.Video.Thumbnails.MICRO_KIND);

            //加入缓存中
            if (getVideoThumbToCache(params[0]) == null) {
                addVideoThumbToCache(path, bitmap);
            }
            return bitmap;
        }

        @Override
        protected void onPostExecute(Bitmap bitmap) {
            if (imgView.getTag().equals(path)) {//通过 Tag可以绑定 图片地址和 imageView，这是解决Listview加载图片错位的解决办法之一
                imgView.setImageBitmap(bitmap);
            }
        }
    }
}