Question

我从Fragment1调用AsyncTask类并尝试在Fragment2的listview中存储doInBackground（）的结果。

但是当我使用Fragment2的视图来访问像

这样的元素时

cartlistview=(ListView)v.findViewById(R.id.listview1);

抛出空指针异常，声明v为空。

我在onPosteExecute（）函数中编写了存储代码

  protected void onPostExecute(String result) {
     MyCartFragment mcf=new MyCartFragment(); //2nd Fragment
     View v=mcf.getView();         
     cartlistview=(ListView)v.findViewById(R.id.listView1); // ERROR HERE

     // Code starting from here is not causing any problems - ignoreable.
     Cursor res=databaseHelper.onView();
     int len=res.getCount();

     listCartItems = new ArrayList<CartItems>();
     listCartItems.add(new CartItems(9,"Item Name", "Quantity", "Price","Delete"));

    if(len==0)
    {
        //Toast.makeText(this.getContext(),"Cart is Empty.",Toast.LENGTH_SHORT).show();
        statusOfCart=false;
    }
    else {
        while (res.moveToNext()) {
            int id=res.getInt(0);
            String itemname = res.getString(1).toString();  // 0 is id, 1 is name, 2 is qty, 3 price
            String itemqty = Integer.toString(res.getInt(2));
            String itemprice = Integer.toString(res.getInt(3)); 
            listCartItems.add(new CartItems(id,itemname, itemqty, itemprice,"X"));
        }
    }
    CartListAdapter cartListAdapter = new CartListAdapter(mcf.getContext(),R.layout.cartlist_layout, listCartItems);
    cartlistview.setAdapter(cartListAdapter);

}

Answer 1

在查找内容之前，您必须给视图充气。

 MyCartFragment mcf=new MyCartFragment(); //2nd Fragment
 View v= inflater.inflate(R.layout.fragment2, container, false); // <= inflate your view
 cartlistview=(ListView)v.findViewById(R.id.listView1); // v is not null anymore

Fragment.getView()只有在视图已经膨胀后才能生效

AsyncTask - 使用不同片段的findviewbyid元素

1 个答案: