Android 如何在 ListView 中更新 ProgressBar 进度

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ListView
        android:id="@+id/list_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </ListView>

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="50dp"
    android:orientation="horizontal">


    <ProgressBar
        android:id="@+id/progress_bar"
        style="@style/Widget.AppCompat.ProgressBar.Horizontal"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:max="100" />

    <Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:text="download" />

</LinearLayout>

public class MainActivity extends AppCompatActivity {
    private ListView listView;          //列表控件
    private List<MyObject> data;       //数据源（模拟）
    private MyAdapter adapter;        //自定义适配器

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        /* 初始化控件 */
        listView = (ListView) findViewById(R.id.list_view);
        /* 初始化数据 */
        data = new ArrayList<>();
        for (int i = 0; i < 30; i++) {
            //组装数据
            MyObject myObject = new MyObject();
            myObject.text = "按钮" + i;
            myObject.isComplete = false;
            //添加到数据源
            data.add(myObject);
        }
        /* 填充适配器 */
        adapter = new MyAdapter(this, data);
        listView.setAdapter(adapter);
    }

    /**
     * 实体对象，用于保存数据
     */
    class MyObject {
        Boolean isComplete;     //下载是否完成
        String text;            //按钮文字
    }

}

public class MyAdapter extends BaseAdapter {
    private Context context;                        //上下文对象用于视图填充
    private List<MainActivity.MyObject> data;       //需要适配的数据源
    private List<View> viewList;                    //View对象集合

    public MyAdapter(Context context, List<MainActivity.MyObject> data) {
        this.viewList = new ArrayList<>();
        this.context = context;
        this.data = data;
    }

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

    @Override
    public Object getItem(int position) {
        return data.get(position);
    }

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

    @Override
    public View getView(final int position, View convertView, ViewGroup parent) {
        final ViewHolder viewHolder;
        /* 初始化控件 */
        if (convertView == null) {
            convertView = LayoutInflater.from(context).inflate(R.layout.list_item, parent, false);
            viewHolder = new ViewHolder();
            viewHolder.progressBar = (ProgressBar) convertView.findViewById(R.id.progress_bar);
            viewHolder.button = (Button) convertView.findViewById(R.id.btn);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }
        /* 添加控件样式 */
        final MainActivity.MyObject myObject = data.get(position);
        viewHolder.button.setText(myObject.text);
        //进度条初始化时设置进度
        if (myObject.isComplete) {
            viewHolder.progressBar.setProgress(100);
        } else {
            viewHolder.progressBar.setProgress(0);
        }
        /* 设置按钮点击事件 */
        viewHolder.button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (viewHolder.progressBar.getProgress() == 0) {
                    //如果未开始下载，启动异步下载任务
                    MyAsyncTask asyncTask = new MyAsyncTask(viewList, position);
                    //添加THREAD_POOL_EXECUTOR可启动多个异步任务
                    asyncTask.executeOnExecutor(MyAsyncTask.THREAD_POOL_EXECUTOR,myObject);
                }
            }
        });
        /* 标识View对象 */
        //将list_view的ID作为Tag的Key值
        convertView.setTag(R.id.list_view, position);//此处将位置信息作为标识传递
        viewList.add(convertView);

        return convertView;
    }

    /**
     * 用于缓存控件ID
     */
    class ViewHolder {
        ProgressBar progressBar;
        Button button;
    }
}

public class MyAsyncTask extends AsyncTask<MainActivity.MyObject, Integer, Void> {
    private MainActivity.MyObject myObject;     //单个数据，用于完成后的处理
    private List<View> viewList;                //视图对象集合，用于设置样式
    private Integer viewId;                     //视图标识，用于匹配视图对象

    public MyAsyncTask(List<View> viewList, Integer viewId) {
        this.viewList = viewList;
        this.viewId = viewId;
    }

    @Override
    protected Void doInBackground(MainActivity.MyObject... params) {
        myObject = params[0];
        /* 模拟下载任务 */
        for (int i = 0; i < 100; i++) {
            //发布进度
            publishProgress(i);
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    @Override
    protected void onProgressUpdate(Integer... values) {
        View view = null;
        /* 匹配视图对象 */
        for (int i = 0; i < viewList.size(); i++) {
            if (viewList.get(i).getTag(R.id.list_view) == viewId) {
                //检查所有视图ID，如果ID匹配则取出该对象
                view = viewList.get(i);
                break;
            }
        }
        if (view != null) {
            //将视图对象中缓存的ViewHolder对象取出，并使用该对象对控件进行更新
            MyAdapter.ViewHolder viewHolder = (MyAdapter.ViewHolder) view.getTag();
            viewHolder.progressBar.setProgress(values[0]);
        }
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        //更新数据源信息
        myObject.isComplete = true;
    }
}