Android: Der Versuch, virtuelle Methode ‚Leeren android.widget.ListView.setAdapter (android.widget.ListAdapter)‘ auf eine Null-Objekt Referenz

Question

ich eine Listenansicht zu machen versuchen aufzuzurufen, die Bilder und Text in einer anderen Aktivität enthält. Ich bin nicht so konzentriert in Android-Programmierung, also im Grunde wie ein Neuling in Android-Programmierung und ich habe Schwierigkeiten beim Debuggen meiner App. Bitte helfen Sie mir :)

Fehler:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference 
    at com.fingervoiz.app.tamla.Activity.ListDataIdntActivity.onCreate(ListDataIdntActivity.java:53) 

komplette LogCat:

E/AndroidRuntime: FATAL EXCEPTION: main 
Process: com.fingervoiz.app.tamla, PID: 14968 
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fingervoiz.app.tamla/com.fingervoiz.app.tamla.Activity.ListDataIdntActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference 
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2534) 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2608) 
    at android.app.ActivityThread.access$800(ActivityThread.java:178) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470) 
    at android.os.Handler.dispatchMessage(Handler.java:111) 
    at android.os.Looper.loop(Looper.java:194) 
    at android.app.ActivityThread.main(ActivityThread.java:5637) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:372) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:959) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754) 
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference 
    at com.fingervoiz.app.tamla.Activity.ListDataIdntActivity.onCreate(ListDataIdntActivity.java:53) 
    at android.app.Activity.performCreate(Activity.java:6092) 
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1112) 
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2481) 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2608)  
    at android.app.ActivityThread.access$800(ActivityThread.java:178)  
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1470)  
    at android.os.Handler.dispatchMessage(Handler.java:111)  
    at android.os.Looper.loop(Looper.java:194)  
    at android.app.ActivityThread.main(ActivityThread.java:5637)  
    at java.lang.reflect.Method.invoke(Native Method)  
    at java.lang.reflect.Method.invoke(Method.java:372)  
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:959)  
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:754)  

Mein Code: (Adapter)

public class ListDIDadapter extends ArrayAdapter<TamlaDataIdntModel> { 

    Context context; 
    int layoutResID; 

    ArrayList<TamlaDataIdntModel> dataToList = new ArrayList<TamlaDataIdntModel>(); 

    public ListDIDadapter(Context context, int layoutResID, ArrayList<TamlaDataIdntModel> dataToList){ 
     super(context,layoutResID,dataToList); 
     this.layoutResID = layoutResID; 
     this.context = context; 
     this.dataToList = dataToList; 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 

     View view = convertView; 
     Holder holder = null; 

     if (view == null){ 
      LayoutInflater inflater = ((Activity) context).getLayoutInflater(); 
      view = inflater.inflate(layoutResID,parent,false); 

      holder = new Holder(); 
      holder.txtFname = (TextView) view.findViewById(R.id.did_item_fullname); 
      holder.txtGender = (TextView) view.findViewById(R.id.did_item_gender); 
      holder.txtBplace = (TextView) view.findViewById(R.id.did_item_bplace); 
      holder.txtBday = (TextView) view.findViewById(R.id.did_item_bday); 
      holder.txtAddress = (TextView) view.findViewById(R.id.did_item_address); 
      holder.imgProfile = (ImageView) view.findViewById(R.id.did_item_profilepic); 
      view.setTag(holder); 
     }else { 
      holder = (Holder) view.getTag(); 
     } 

     //FILL 
     TamlaDataIdntModel dids = dataToList.get(position); 
     if(dids != null){ 
      holder.txtFname.setText(dids.get_lname()+", "+dids.get_fname()+" "+dids.get_mname()); 
      holder.txtGender.setText(dids.get_gender()); 
      holder.txtBplace.setText(dids.get_bplace()); 
      holder.txtBday.setText(dids.get_bday()); 
      holder.txtAddress.setText(dids.get_address()); 

      byte[] outImage = dids.get_dp(); 
      ByteArrayInputStream imageStream = new ByteArrayInputStream(outImage); 
      Bitmap theImage = BitmapFactory.decodeStream(imageStream); 
      holder.imgProfile.setImageBitmap(theImage); 
     } 

     return view; 
    } 

    static class Holder{ 
     TextView txtFname; 
     TextView txtGender; 
     TextView txtBplace; 
     TextView txtBday; 
     TextView txtAddress; 
     ImageView imgProfile; 
    } 
} 

(Liste Aktivität)

public class ListDataIdntActivity extends Activity{ 

    public static final String TAG = "ListDataIdntActivity"; 

    public static final int REQUEST_CODE_ADD_COMPANY = 40; 
    public static final String EXTRA_ADDED_COMPANY = "extra_key_added_did"; 

    private ListView mListViewDID; 
    private TextView emptyTxt; 
    private Button b1; 

    private ListDIDadapter adapter; 
    private ArrayList<TamlaDataIdntModel> arryList; 
    private DataIdntDAO mDIDdao; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     //Initialize View 
     mListViewDID = (ListView) findViewById(R.id.list_did); 
     emptyTxt = (TextView) findViewById(R.id.txt_empty_list_dids); 
     b1 = (Button) findViewById(R.id.back_list_did); 

     //Fill List View 
     mDIDdao = new DataIdntDAO(this); 
     List<TamlaDataIdntModel> mIdntList = mDIDdao.getAllDID(); 

     if (mIdntList != null && !mIdntList.isEmpty()){ 
      adapter = new ListDIDadapter(this,R.layout.activity_list_did,arryList); 
      mListViewDID.setAdapter(adapter); 
     }else { 
      emptyTxt.setVisibility(View.VISIBLE); 
      mListViewDID.setVisibility(View.GONE); 
     } 

    } 


    @Override 
    protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
     if(requestCode == REQUEST_CODE_ADD_COMPANY){ 
      if(requestCode == RESULT_OK){ 
       // add the added identity to the list and refresh the list view 
       if(data != null){ 
        TamlaDataIdntModel createdNewDID = (TamlaDataIdntModel)data.getSerializableExtra(EXTRA_ADDED_COMPANY); 
        if(createdNewDID != null){ 
         if(arryList == null){ 
          arryList = new ArrayList<TamlaDataIdntModel>(); 
          arryList.add(createdNewDID); 

          if (adapter == null){ 
           if (mListViewDID.getVisibility() != View.VISIBLE){ 
            mListViewDID.setVisibility(View.VISIBLE); 
            emptyTxt.setVisibility(View.GONE); 
           } 

           adapter = new ListDIDadapter(this,R.layout.activity_list_did,arryList); 
           mListViewDID.setAdapter(adapter); 
          }else { 

           if (arryList != null){ 

            for (Object object : arryList) { 

             adapter.insert((TamlaDataIdntModel) object, adapter.getCount()); 
            } 
           } 
           adapter.notifyDataSetChanged(); 
          } 
         } 
        } 

       } 
      } 
     } else { 
      super.onActivityResult(requestCode,resultCode,data); 
     } 
    } 

    @Override 
    protected void onDestroy() { 
     super.onDestroy(); 
     mDIDdao.close(); 
    } 
} 

Answer 1

Sie verpassen eine sehr wichtige Linie - setContentView(). Diese Zeile bindet das XML an die Ansicht der Aktivität und es ist die Ansicht, die für findViewById verwendet wird. Fügen Sie diese Zeile in onCreate:

@Override 
public void onCreate(Bundle state){ 
    super.onCreate(state); 
    setContentView(R.layout.name_of_the_xml); 

Answer 2

Sie haben das Layout MainActivity hinzuzufügen (die die Listview enthält) vor der Verwendung findViewById()

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    setContent(R.layout_MAIN_LAYOUT_ACTIVITY); 
    //Initialize View 
    mListViewDID = (ListView) findViewById(R.id.list_did); 
}