Firebase Recylerview löst NullPointerException in populateView

Question

leider habe ich ein Problem, das ich nicht lösen kann. Deshalb brauche ich deine Hilfe. Wenn ein neuer Benutzer hinzugefügt wird und die BenutzerActivity (KontaktActivity) geöffnet ist, stürzt die App manchmal ab. Bitte lassen Sie mich wissen, wenn ich etwas vergessen habe, die für die Problemlösung

hier hilfreich ist der Code des userActivity:

import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.support.v7.widget.LinearLayoutManager; 
import android.support.v7.widget.RecyclerView; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ImageView; 
import android.widget.LinearLayout; 
import android.widget.ProgressBar; 
import android.widget.TextView; 

import com.bumptech.glide.Glide; 
import com.bumptech.glide.load.engine.DiskCacheStrategy; 
import com.firebase.ui.database.FirebaseRecyclerAdapter; 
import com.google.firebase.database.DatabaseReference; 
import com.google.firebase.database.FirebaseDatabase; 

public class KontakteActivity extends AppCompatActivity { 

    TextView kontakt_name,kontakt_email; 
    RecyclerView recyclerView; 
    FirebaseDatabase firebaseDatabase; 
    DatabaseReference mDatabaseReference; 
    public FirebaseRecyclerAdapter<FirebaseDB_helper,Kontakte_Viewholder> mFirebaseAdapter; 
    ProgressBar progressBar; 
    LinearLayoutManager linearLayoutManager; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_kontakte); 


     //DB 
     firebaseDatabase = FirebaseDatabase.getInstance(); 
     mDatabaseReference = firebaseDatabase.getReference("Users"); 
     mDatabaseReference.keepSynced(true); 

     //Views 
     progressBar = (ProgressBar)findViewById(R.id.progressBar_act_kontakte); 

     recyclerView = (RecyclerView)findViewById(R.id.recylerView_kontakte_act_kontakte); 

     linearLayoutManager = new LinearLayoutManager(KontakteActivity.this); 


     recyclerView.setLayoutManager(linearLayoutManager); 
    } 


    @Override 
    protected void onStart() { 
     super.onStart(); 

     progressBar.setVisibility(ProgressBar.VISIBLE); 


     mFirebaseAdapter = new FirebaseRecyclerAdapter<FirebaseDB_helper, Kontakte_Viewholder> 
       (FirebaseDB_helper.class, R.layout.kontakte_card_view, Kontakte_Viewholder.class, mDatabaseReference) { 


      public void populateViewHolder(final Kontakte_Viewholder viewholder , FirebaseDB_helper model, final int position) 
      { 

       progressBar.setVisibility(View.INVISIBLE); 

        viewholder.Kontakt_Name(model.getName()); 
        viewholder.Kontakt_Image(model.getImage_Url()); 
        if (model.getEmail().equals(MainActivity.User_email)) 
        { 
         viewholder.Layout_hide(); 
        }else { 
         viewholder.Kontakt_Email(model.getEmail()); 
        } 

      } 
     }; 

     mFirebaseAdapter.notifyDataSetChanged(); 

     recyclerView.setAdapter(mFirebaseAdapter); 


    } 

// /* 

    public static class Kontakte_Viewholder extends RecyclerView.ViewHolder{ 

     private final TextView kontakt_name,kontakt_email; 
     private final ImageView kontakt_image; 
     private final LinearLayout layout; 
     final LinearLayout.LayoutParams params; 

     public Kontakte_Viewholder(final View itemView) { 
      super(itemView); 

      kontakt_name=(TextView)itemView.findViewById(R.id.txt_name_kontakt_card); 
      kontakt_email=(TextView)itemView.findViewById(R.id.txtView_email_kontakt_card); 
      kontakt_image=(ImageView)itemView.findViewById(R.id.imageView_kontakt_card); 
      layout = (LinearLayout)itemView.findViewById(R.id.linearlayout_kontakt_card_view); //Probleeeeeem 
      params = new LinearLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);//erforderlich um ein LinearLayout anzupassen 
     } 

     private void Kontakt_Name(String name) 
     { 
      kontakt_name.setText(name); 
     } 

     private void Layout_hide() 
     { 
      params.height=0; 
      layout.setLayoutParams(params); 
     } 

     private void Kontakt_Email (String email) 
     { 
      kontakt_email.setText(email); 
     } 

     private void Kontakt_Image (String Url) 
     { 
      if (!Url.equals("Null")){ 
       Glide.with(itemView.getContext()) 
         .load(Url) 
         .crossFade() 
         .thumbnail(0.5f) 
         .placeholder(R.drawable.loading) 
         .diskCacheStrategy(DiskCacheStrategy.ALL) 
         .into(kontakt_image); 
      } 
     } 


    }//*/ 
} 

Hier ist der Crash-Bericht von Android Studio

E/AndroidRuntime: FATAL EXCEPTION: main 
    Process: com.example.zare.ma_firechat, PID: 9510 
    java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference 
     at com.example.zare.ma_firechat.KontakteActivity$Kontakte_Viewholder.Kontakt_Image(KontakteActivity.java:129) 
     at com.example.zare.ma_firechat.KontakteActivity$Kontakte_Viewholder.access$100(KontakteActivity.java:94) 
     at com.example.zare.ma_firechat.KontakteActivity$1.populateViewHolder(KontakteActivity.java:74) 
     at com.example.zare.ma_firechat.KontakteActivity$1.populateViewHolder(KontakteActivity.java:61) 
     at com.firebase.ui.database.FirebaseRecyclerAdapter.onBindViewHolder(FirebaseRecyclerAdapter.java:184) 
     at android.support.v7.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:6356) 
     at android.support.v7.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:6389) 
     at android.support.v7.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:5335) 
     at android.support.v7.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:5598) 
     at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5440) 
     at android.support.v7.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:5436) 
     at android.support.v7.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2224) 
     at android.support.v7.widget.LinearLayoutManager.layoutChunk(LinearLayoutManager.java:1551) 
     at android.support.v7.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1511) 
     at android.support.v7.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:595) 
     at android.support.v7.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:3583) 
     at android.support.v7.widget.RecyclerView.onMeasure(RecyclerView.java:3025) 
     at android.view.View.measure(View.java:19734) 
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120) 
     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464) 
     at android.widget.LinearLayout.measureVertical(LinearLayout.java:758) 
     at android.widget.LinearLayout.onMeasure(LinearLayout.java:640) 
     at android.view.View.measure(View.java:19734) 
     at android.support.constraint.ConstraintLayout.onMeasure(ConstraintLayout.java:1028) 
     at android.view.View.measure(View.java:19734) 
     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6120) 
     at android.widget.FrameLayout.onMeasure(FrameLayout.java:185) 
     at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139) 
     at android.view.View.measure(View.java:19734) 

Answer 1

Eingangsparameter in private void Kontakt_Image (String Url) ist null. Sie müssen Null überprüfen.

private void Kontakt_Image (String Url) 
    { 
     if (Url!=null && !Url.equals("Null")){ 
      Glide.with(itemView.getContext()) 
        .load(Url) 
        .crossFade() 
        .thumbnail(0.5f) 
        .placeholder(R.drawable.loading) 
        .diskCacheStrategy(DiskCacheStrategy.ALL) 
        .into(kontakt_image); 
     } 
    }