super（context，textviewid）;显示java.lang.NullPointerException

3 回答

• 0

  我相信这是因为你传递了一个空的上下文 .

  尝试：

  public void onWindowFocusChanged(boolean hasFocus) {
      super.onWindowFocusChanged(hasFocus);
      if (hasFocus) {
          ((DownloadFragment) downloads).refreshlist(this);
      }
  }
  

  DownloadFragment.java

  public class MyAdapter extends ArrayAdapter<AdapterItem> {
      public MyAdapter(Context context, int textviewid) {
          super(context, textviewid); // NPE here
      }
  
      public void refreshlist(Context context) {
          items.clear();
          adapter = new MyAdapter(context, 0);
          // ...
      }
  }
  

  您是否尝试使用新数据刷新适配器？你试过notifyDataSetChanged（）吗？

  public void onWindowFocusChanged(boolean hasFocus) {
      super.onWindowFocusChanged(hasFocus); 
      if (hasFocus) { 
         DownloadFragment.adapter.notifyDataSetChanged(); 
      } 
  }
  

  回复于 2024-04-25T06:58:27+08:00
• 0

  Fragment类中的getActivity（）方法返回null，直到它附加到Activity，即直到调用onAttach（Activity）方法 . 所以最好在Fragment的onActivityCreated（）方法中为MyAdapter类创建对象 .

  试试这个...

  public class DownloadFragment extends Fragment {
      private MyAdapter adapter;
  
      @Override
      public void onActivityCreated(Bundle savedInstanceState) {
          super.onActivityCreated(savedInstanceState);
          adapter = new MyAdapter(getActivity(),0);
      }
  }
  

  回复于 2024-04-25T06:58:27+08:00
• 0

  您的适配器应该是这样的

  package com.example.demo;
  
  import java.util.ArrayList;
  
  import android.content.Context;
  import android.database.DataSetObserver;
  import android.util.Log;
  import android.view.View;
  import android.view.ViewGroup;
  import android.widget.ArrayAdapter;
  
  public class SmartListAdapterWithHolder extends ArrayAdapter<AdapterItem> {
  
      private Context context;
      private ArrayList<String> items;
  
      public SmartListAdapterWithHolder(Context context, int resource, ArrayList<AdapterItem> items) {
          super(context, resource, items);
          this.items = items;
          this.context = context;
      }
  
      public ArrayList<AdapterItem> getSmartListItems() {
          return items;
      }
  
      @Override
      public void registerDataSetObserver(DataSetObserver observer) {
          Log.v("SmartListAdapter", observer.toString());
          super.registerDataSetObserver(observer);
      }
  
      @Override
      public View getView(int position, View convertView, ViewGroup parent) {
  
          return convertView;
      }
  
  }
  

  回复于 2024-04-25T06:58:27+08:00