Question

在我的MainActivity中，我有一个listview，每行有两行文本。应用程序启动时只写第一行，第二行必须根据AsyncTask类处理的内容编写。当我尝试这样做时，listview的第一项获取AsyncTask提供的所有值，因为我不明白如何更新仅列表视图的第二行每个项目，无需重写整个列表视图。每个textView在xml布局文件中都有自己的id。我怎么能在onPostExecute（）中做到这一点？这是代码：

在MainActivity onCreate（）中：

final ListView listview = (ListView) findViewById(R.id.listview); final String[] values = new String[10]; for(int i=0;i<10;i++){ //do stuff to write the values[] elements } MySimpleArrayAdapter adapter = new MySimpleArrayAdapter(this, values); listview.setAdapter(adapter);

MySimpleArrayAdapter类：

public class MySimpleArrayAdapter extends ArrayAdapter<String> { private final Context context; private final String[] values; int position=0; public MySimpleArrayAdapter(Context context, String[] values) { super(context, R.layout.list_layout, values); this.context = context; this.values = values; } @Override public View getView(int position, View convertView, ViewGroup parent) { LayoutInflater inflater = (LayoutInflater) context .getSystemService(Context.LAYOUT_INFLATER_SERVICE); View rowView = inflater.inflate(R.layout.list_layout, parent, false); TextView firstLine = (TextView) rowView.findViewById(R.id.label); TextView secondLine = (TextView) rowView.findViewById(R.id.sublabel); firstLine.setText(values[position]); secondLine.setText(""); //I prefer to write an empty string for the secondLine return rowView; } }

AsyncTask：

private class Process extends AsyncTask<Void, Void, String> { @Override protected String doInBackground(Void... params) { //do stuff } @Override protected void onPostExecute(String message) { TextView secondLine = (TextView) findViewById(R.id.sublabel); //This of course udpdates only the secondLine of the first item of listview secondLine.setText(processedValues); } }

Answer 1

将TextView作为参数传递给AsyncTask，如下所示

private class Process extends AsyncTask<Void, Void, String> {
private WeakReference<TextView> weakTextView;
public Process(TextView textView){
       weakTextView = new WeakReference<TextView>(textView);
}
@Override
protected String doInBackground(Void... params) {
    //do stuff
}

@Override
protected void onPostExecute(String message) {
    TextView tv = weakTextView.get();
   if(tv!=null){
       tv.setText(message);
 }
}

}

您在getView中将其称为

Process p = new Process(yourTextView);
p.execute();

//方法二

private class Process extends AsyncTask<TextView, Void, String> {

private WeakReference<TextView> weakTextView;

@Override
protected String doInBackground(TextView... params) {
    if(params == null||params.length=0){
         return null;
    }
    TextView tv = (TextView)params[0];
    weakTextView = new WeakReference<TextView>(tv);

    //do stuff
}

@Override
protected void onPostExecute(String message) {
    TextView tv = weakTextView.get();
   if(tv!=null){
       tv.setText(message);
 }
}

}

您在getView中将其称为

Process p = new Process();
p.execute(yourTextView);

//方法3

只需更新此列表适配器的下划线数据对象并致电adapter.notifyDataSetChanged();
这将再次致电getView 除非您正在显示来自互联网的图像

，否则在大多数情况下，此方法优于上述其他2种方法

如何从AsyncTask更改或设置列表视图的子项？

1 个答案: