java.lang.NullPointerException: próba wywołania metody wirtualnej "android.view.View android.app.Activity.findViewById (int)" na odwołanym obiekcie o wartości zerowej

Question

Zawsze pojawia się błąd w moim projekcie Android.

java.lang.NullPointerException: próba wywołania sposób wirtualnego 'android.view.View android.app.Activity.findViewById (int)' na NULL referencyjnego obiektu

moim główną działalność Dzwonię do klasy FragmentStart.

FragmentStart.class

import android.app.Activity; 
 
import android.content.Intent; 
 
import android.os.Bundle; 
 
import android.support.v4.app.Fragment; 
 
import android.view.LayoutInflater; 
 
import android.view.View; 
 
import android.view.ViewGroup; 
 
import android.widget.AdapterView; 
 
import android.widget.ArrayAdapter; 
 
import android.widget.Button; 
 
import android.widget.ListView; 
 

 
public class FragmentStart extends Fragment { 
 

 
    //Define Listview 
 
    private ListView startList; 
 
    private String[] stringList; 
 
    Activity activity = getActivity(); 
 

 
    public FragmentStart() { 
 
     // 
 
    } 
 

 

 
    @Override 
 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
 
     View rootView = inflater.inflate(R.layout.fragment_start, container, false); 
 

 
     // Create ListView start 
 
     startList = (ListView) rootView.findViewById(R.id.startList); 
 
     stringList = getResources().getStringArray(R.array.startList); 
 

 
     if (activity != null) { 
 
      ArrayAdapter<String> objAdapter = new ArrayAdapter<String>(activity, android.R.layout.simple_list_item_1, stringList); 
 
      startList.setAdapter(objAdapter); 
 
      startList.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
 

 
       @Override 
 
       public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 
 
        switch (startList.getPositionForView(view)) { 
 

 
         case 0: 
 
          // ... 
 
          break; 
 

 
        } 
 
       } 
 
      }); 
 
     } 
 
     // Create ListView end 
 

 
     //New Entry 
 
     Button add = (Button) activity.findViewById(R.id.add); 
 
     add.setOnClickListener(new View.OnClickListener() { 
 
      public void onClick(View view) { 
 
       Intent myIntent = new Intent(view.getContext(), addItem.class); 
 
       startActivityForResult(myIntent, 0); 
 
      } 
 

 
     }); 
 

 
     return rootView; 
 
    } 
 
}

Answer 1

Oprócz tego, co @Selvin wskazał, wygląda to tak:

Button add = (Button) activity.findViewById(R.id.add); 

... powinny być zmieniane do tego:

Button add = (Button) rootView.findViewById(R.id.add); 

Answer 2

Użyj następującego kodu:

listView1.setOnItemClickListener(new AdapterView.OnItemClickListener() { 
     @Override 
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) { 

     //  selectedPosition = position; 

      View newTypeView=listView1.getChildAt(position-listView1.getFirstVisiblePosition()).findViewById(R.id.RelativeLayout); 

      if (newTypeView.getClass().getName().toString().contains("RelativeLayout")) { 


       if (lastTouchedVw != null) 
        lastTouchedVw.setBackgroundColor(Color.parseColor("#ffffff")); 
       // mainImageView.setImageURI(Uri.parse(al.get(position).toString())); 
       //bigImageRelativeLayoutVw.setBackgroundColor(Color.parseColor("#ffb000")); 
        newTypeView.setBackgroundResource(R.drawable.cellbg); 

        lastTouchedVw = newTypeView; 
      }