【达内课程】音乐播放器4.0(图片显示)

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ListView中异步批量加载图片业务
使用单线程轮循任务队列的机制完成该业务

效果图

MusicAdapter

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

import com.example.xx.v4.R;
import com.example.xx.v4.entity.Music;
import com.example.xx.v4.util.HttpUtils;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
/**
 * 音乐列表适配器
 */
public class MusicAdapter extends BaseAdapter {
    private Context context;
    private List<Music> musics;
    private LayoutInflater inflater;
    private List<ImageLoaderTask> tasks = new ArrayList<ImageLoaderTask>();
    private Thread workThread;
    private boolean isLoop = true;
    private ListView listView;
    private Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what){
                case HANDLER_IMAGE_LOAD_SUCCESS:
                    //给相应的Imageview设置bitmap
                    ImageLoaderTask task = (ImageLoaderTask)msg.obj;
                    Bitmap bitmap = task.bitmap;
                    ImageView imageView = (ImageView) listView.findViewWithTag(task.path);
                    if(imageView != null){
                        if(bitmap!=null){
                            imageView.setImageBitmap(bitmap);
                        }else {
                            imageView.setImageResource(R.mipmap.ic_launcher);
                        }
                    }
                    break;
            }
        }
    };

    public static final int HANDLER_IMAGE_LOAD_SUCCESS = 1;
    public MusicAdapter(Context context, List<Music> musics, ListView listView) {
        this.context = context;
        this.musics = musics;
        this.inflater = LayoutInflater.from(context);
        this.listView = listView;
        //启动工作线程，轮循任务集合
        workThread = new Thread(){
            @Override
            public void run() {
                while (isLoop){
                    if(!tasks.isEmpty()){//不是空集合
                        ImageLoaderTask task = tasks.remove(0);//remove的同时返回该数据
                        String url = task.path;
                        //发送http请求 下载图片
                        Bitmap bitmap = loadBitmap(url);
                        task.bitmap = bitmap;
                        //更新界面 发消息给Handler
                        Message message = new Message();
                        message.what = HANDLER_IMAGE_LOAD_SUCCESS;
                        message.obj = task;
                        handler.sendMessage(message);

                    }else {//空集合 等待
                        try {
                            //锁
                            synchronized (workThread) {
                                workThread.wait();
                            }
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        };
        workThread.start();
    }

    /**
     * 通过url地址 发送http请求 获取图片
     * @param url
     * @return
     */
    private Bitmap loadBitmap(String url){
        try {
            InputStream is = HttpUtils.getInputStream(url);
            Bitmap bitmap = BitmapFactory.decodeStream(is);
            return bitmap;
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    public int getCount() {
        return musics.size();
    }

    @Override
    public Music getItem(int i) {
        return musics.get(i);
    }

    @Override
    public long getItemId(int i) {
        return i;
    }

    @Override
    public View getView(int i, View view, ViewGroup viewGroup) {
        ViewHolder holder = null;
        if(view == null){
            view = inflater.inflate(R.layout.item_lv_music,null);
            holder = new ViewHolder();
            holder.imgPic = view.findViewById(R.id.img_Pic);
            holder.tvName = view.findViewById(R.id.tv_name);
            holder.tvSinger = view.findViewById(R.id.tv_singer);
            view.setTag(holder);
        }

        holder = (ViewHolder) view.getTag();
        //给控件赋值
        Music music = getItem(i);
        holder.tvName.setText(music.getTitle());
        holder.tvSinger.setText(music.getAuthor());
        //图片在服务器，本来该起线程显示的，但是，这是adapter.getView()方法
        //每次图片显示时，都要启线程的话，手机会炸的...
        //给holder.imgPic设置图片
        //向任务集合中一个图片下载任务
        holder.imgPic.setTag(music.getPic_small());
        ImageLoaderTask task = new ImageLoaderTask();
        task.path = music.getPic_small();
        tasks.add(task);
        //唤醒工作线程,起来干活
        synchronized (workThread) {
            workThread.notify();
        }
        return view;
    }

    class ViewHolder{
        ImageView imgPic;
        TextView tvName;
        TextView tvSinger;
    }

    class ImageLoaderTask{
        String path;//保存图片下载路径
        Bitmap bitmap;//下载成功后的图片
    }
}

NewMusicListFrament修改如下

......
 /**
     * 更新Adapter
     * @param musics
     */
    public void setAdapter(List<Music> musics){
        adapter = new MusicAdapter(getActivity(),musics,listView);
        listView.setAdapter(adapter);
    }

重点都写在注释里了