Viewmodel null after initializing

[lina saeed]

after initializing the ViewModel i keep getting an error of null object reference , and i don't know why

import androidx.lifecycle.LiveData;
import androidx.lifecycle.ViewModel;

import com.example.foodapp.models.Recipe;
import com.example.foodapp.respositories.RecipeRepository;

public class RecipeViewModel extends ViewModel {

    private String mRecipeId;

    private RecipeRepository mRecipeRepository;

    public RecipeViewModel() {
        mRecipeRepository=RecipeRepository.getInstance();
    }

    public LiveData<Recipe>getRecipe(){
        return mRecipeRepository.getRecipe();
    }

    public void searchRecipeById(String recipeId)
    {  mRecipeId = recipeId;
mRecipeRepository.searchRecipeById(recipeId);
    }

    public String getViewModelRecipeId() {
        return mRecipeId;
    }
}

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.ScrollView;
import android.widget.TextView;

import androidx.annotation.Nullable;
import androidx.appcompat.widget.AppCompatImageView;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;

import com.bumptech.glide.Glide;
import com.bumptech.glide.request.RequestOptions;
import com.example.foodapp.models.Recipe;
import com.example.foodapp.viewmodels.RecipeViewModel;

public class RecipeActivity extends BaseActivity {
    private static final String TAG = "RecipeActivity";
    private AppCompatImageView  mRecipeImage;
    private TextView mRecipeTitle ,mRecipeRank;
    private LinearLayout mRecipeIngredientsContainer;

    private ScrollView mScrollView;
    private  RecipeViewModel mRecipeViewModel;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_recipe);
        mRecipeImage=findViewById(R.id.recipe_image);
        mRecipeTitle=findViewById(R.id.recipe_title);
        mRecipeRank=findViewById(R.id.recipe_social_score);
        mRecipeIngredientsContainer=findViewById(R.id.ingredients_container);
        mScrollView=findViewById(R.id.parent);

        mRecipeViewModel=new ViewModelProvider(this).get(RecipeViewModel.class);

        showProgressBar(true);
        subscribeObserver();
        getIncomingIntent();
    }

    private void getIncomingIntent(){
        if(getIntent().hasExtra("recipe")){
            Recipe recipe=getIntent().getParcelableExtra("recipe");
            Log.d(TAG, "getIncomingIntent: "+recipe.getTitle());
            mRecipeViewModel.searchRecipeById(recipe.getRecipeId());
        }
    }

private void subscribeObserver(){

        mRecipeViewModel.getRecipe().observe(this, new Observer<Recipe>() {
            @Override
            public void onChanged(Recipe recipe) {
                if(recipe!=null){
                    if(recipe.getRecipeId().equals(mRecipeViewModel.getViewModelRecipeId())){
                        setRecipeProperties(recipe);
                    }
                }

            }
        });
}

        private void setRecipeProperties(Recipe recipe){

        if(recipe!=null){

            RequestOptions requestOptions= new RequestOptions()
                    .placeholder(R.drawable.ic_launcher_background);

            Glide.with(this).setDefaultRequestOptions(requestOptions)
                    .load(recipe.getImageUrl()).into(mRecipeImage);
            mRecipeTitle.setText(recipe.getTitle());
            mRecipeRank.setText(String.valueOf(recipe.getSocialUrl()));
            mRecipeIngredientsContainer.removeAllViews();
            for(String ingredients: recipe.getIngredients()){
                TextView textView= new TextView(this);
                textView.setText(ingredients);
                textView.setTextSize(15);
                textView.setLayoutParams(new LinearLayout.LayoutParams(
                        ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT
                ));
                mRecipeIngredientsContainer.addView(textView);
            }
        }
        showParent();
        showProgressBar(false);
}

private void showParent(){
        mScrollView.setVisibility(View.VISIBLE);
}
}

and this is the exception am getting:

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
       at com.example.foodapp.RecipeActivity$1.onChanged(RecipeActivity.java:63)
       at com.example.foodapp.RecipeActivity$1.onChanged(RecipeActivity.java:57)
       at androidx.lifecycle.LiveData.considerNotify(LiveData.java:133)
       at androidx.lifecycle.LiveData.dispatchingValue(LiveData.java:151)
       at androidx.lifecycle.LiveData.setValue(LiveData.java:309)
       at androidx.lifecycle.MutableLiveData.setValue(MutableLiveData.java:50)..etc

the model class :

import android.os.Parcelable;
import java.util.Arrays;

public class Recipe implements {
    private String title;
    private String publisher;
    private String imageUrl;
    private String id;
    private String [] ingredients;
    private float socialUrl;

    public Recipe() {
    }

    public Recipe(String title, String publisher, String image_url, String id,
                  String[] ingredients, float socialUrl) {
        this.title = title;
        this.publisher = publisher;
        this.imageUrl = image_url;
        this.id = id;
        this.ingredients = ingredients;
        this.socialUrl = socialUrl;
    }

    
    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getPublisher() {
        return publisher;
    }

    public void setPublisher(String publisher) {
        this.publisher = publisher;
    }

    public String getImageUrl() {
        return imageUrl;
    }

    public void setImageUrl(String imageUrl) {
        this.imageUrl = imageUrl;
    }

    public String getRecipeId() {
        return id;
    }

    public void setRecipeId(String id) {
        this.id = id;
    }

    public String[] getIngredients() {
        return ingredients;
    }

    public void setIngredients(String[] ingredients) {
        this.ingredients = ingredients;
    }

    public float getSocialUrl() {
        return socialUrl;
    }

    public void setSocialUrl(float socialUrl) {
        this.socialUrl = socialUrl;
    }

    @Override
    public String toString() {
        return "Recipe{" +
                "title='" + title + '\'' +
                ", publisher='" + publisher + '\'' +
                ", image_url='" + imageUrl + '\'' +
                ", recipe_id='" + id + '\'' +
                ", ingredients=" + Arrays.toString(ingredients) +
                ", social_rank=" + socialUrl +
                '}';
    }}

I've tried cleaning the project and invalidate and cache and even using the deprecated ViewModelProviders class ,

but all the same and nothing has changed

[Norm Radder]

Is the getRecipeId method returning a null value?
Where is the code that creates a new instance of the Recipe class?  Does it provide a non null value for id?

Please edit your post and wrap each section of code in code tags: Select the code and press the Code button,

[lina saeed]

this is the code for Recipe instance :

 @Override
    public void onRecipeClick(int position) {
        Intent intent = new Intent(this, RecipeActivity.class);
        intent.putExtra("recipe", mAdapter.getSelectedRecipe(position));
        startActivity(intent);
    }

 

public Recipe getSelectedRecipe( int position){
//mRecipes is list of recipes objects
        if(mRecipes!=null){
            if(mRecipes.size()>0){
            return mRecipes.get(position);}
        }
        return null;
  }

when the user clicks on the list of recipes (which are in another activity) an intent is send to the RecipeActivity with the selected recipe instance.

yes getRecipeId is returning a null value , while it should not.

[Norm Radder]

Where is the code that creates a new instance of the Recipe class?  
Does it provide a non null value for id?

[lina saeed]

there is no such code for creating an instance of the Recipe class , Recipe instance is a model object for the data that am getting through an API using retrofit , when i want a particular recipe details i click an item in my Recipes list and i use the recipe id that I've clicked to get the entire details , those details are obtained via the intent that opens another activity (RecipeActivity)

my previous reply is where the recipe instance is being assigned a value .

i used a breakpoint on the code line(      mRecipeViewModel.searchRecipeById(recipe.getRecipeId()); (line 49)) in which i got a value for the id;

but when i did another breakpoint on line (  if(recipe.getRecipeId().equals(mRecipeViewModel.getViewModelRecipeId())) line (59) the id was null

[Norm Radder]

Can you add some debug code to the Recipe class that prints out the value of id when the constructor is called and when the the setRecipeId method is called to see if id ever has a valid value?

Your debugging shows that sometimes id has a valid value and sometimes it is null.  You need to fix the case for it being null.

[lina saeed]

can you please help me to write such code , am new to the android programming

[Norm Radder]

You have posted the same contents for your last two posts.  You might have missed my post.

[lina saeed]

i did not miss it , but am new to the website am trying to find my way around it , i asked for help for such debugging code , because am kinda new to android programming .

[Norm Radder]

help for such debugging code ,

I use print statements for debugging:

 
   //  Add following to constructor
   System.out.println("cons id="+id);  // show id in constructor
   ...
   // Add following to setRecipeId method
   System.out.println("set id="+id);   // show id in setRecipeId method
   

The printed lines will be in the logcat.

[lina saeed]

The logcat showed me that the id in the constructor is 0.
it did not print out the setRecipeId().

[Norm Radder]

So that print out in the logcat shows that only one instance of the Recipe class was created and that the value for id was "0".
Does that make sense?  Is that the correct id value?

[lina saeed]

No it dose not make sense , and of course that's not the correct value for the id . help please    


in the displaySearchCategory() i create an instance of the recipe, maybe that's why i have to different id values?
 
this is in the adapter class

   public void displaySearchCategories(){

   List<Recipe> categories= new ArrayList<>();
   for (int i=0 ; i< Constant.DEFAULT_SEARCH_CATEGORIES.length;i++){
       Recipe recipe= new Recipe();
       recipe.setTitle(Constant.DEFAULT_SEARCH_CATEGORIES[i]);
       recipe.setImageUrl(Constant.DEFAULT_SEARCH_CATEGORY_IMAGES[i]);
       recipe.setSocialUrl(-1);
       categories.add(recipe);

   }
        mRecipes = categories;
        notifyDataSetChanged();
    }
   

[lina saeed]

this is the whole adapter class

package com.example.foodapp.adapters;

import android.net.Uri;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.bumptech.glide.Glide;
import com.bumptech.glide.request.RequestOptions;
import com.example.foodapp.R;
import com.example.foodapp.models.Recipe;
import com.example.foodapp.util.Constant;

import java.util.ArrayList;
import java.util.List;

public class RecipeRecyclerAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
    private List<Recipe> mRecipes;
    private OnRecipeListener mOnRecipeListener;
    private static final int RECIPE_TYPE=1;
    private static final int LOADING_TYPE=2;
    private static final int CATEGORY_TYPE=3;

    public RecipeRecyclerAdapter (OnRecipeListener mOnRecipeListener) {

        this.mOnRecipeListener = mOnRecipeListener;
    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

        View view =null;
        switch (viewType){
            case RECIPE_TYPE :{
                view = LayoutInflater.from(parent.getContext())
                        .inflate(R.layout.layout_recipe_list_item,parent,false);
                return new RecipeViewHolder(view, mOnRecipeListener);}

            case LOADING_TYPE:{
                view = LayoutInflater.from(parent.getContext())
                        .inflate(R.layout.layout_loading_list_item,parent,false);
                return new LoadingViewHolder(view);}

            case CATEGORY_TYPE:{
                view = LayoutInflater.from(parent.getContext())
                        .inflate(R.layout.layout_category_list_item,parent,false);
                return new CategoryViewHolder(view,mOnRecipeListener);
            }

            default:{
                view = LayoutInflater.from(parent.getContext())
                        .inflate(R.layout.layout_recipe_list_item,parent,false);
                return new RecipeViewHolder(view, mOnRecipeListener);}
        }
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        int itemViewType=getItemViewType(position);
        if(itemViewType==RECIPE_TYPE){
            RequestOptions requestOptions= new RequestOptions().placeholder(R.drawable.ic_launcher_background);

            Glide.with(holder.itemView.getContext()).setDefaultRequestOptions(requestOptions)
                    .load(mRecipes.get(position).getImageUrl()).into(((RecipeViewHolder) holder).image);


            ((RecipeViewHolder)holder).title.setText(mRecipes.get(position).getTitle());
            ((RecipeViewHolder)holder).publisher.setText(mRecipes.get(position).getPublisher());
            ((RecipeViewHolder)holder).socialScore.setText(String.valueOf(Math.round(mRecipes.get(position).getSocialUrl())));

        }
        else if(itemViewType==CATEGORY_TYPE){
            RequestOptions requestOptions = new RequestOptions()
                    .placeholder(R.drawable.ic_launcher_background);
           // Uri path=Uri.parse("android.resource://com.example.foodapp/drawable/" + );
            Glide.with(holder.itemView.getContext())
                    .setDefaultRequestOptions(requestOptions)
                    .load(mRecipes.get(position).getImageUrl())
                    .into(((CategoryViewHolder)holder).categoryImage);

            ((CategoryViewHolder)holder).categoryTitle.setText(mRecipes.get(position).getTitle());



        }

    }

    @Override
    public int getItemViewType(int position) {

        if (mRecipes.get(position).getSocialUrl()==-1){
            return CATEGORY_TYPE;
        }
       else if(mRecipes.get(position).getTitle().equals("LOADING...")){ return  LOADING_TYPE;}
       else if(position==mRecipes.size()-1 && position!=0
        && !mRecipes.get(position).getTitle().equals("EXHAUSTED...")) {
            return  LOADING_TYPE;
        }


        else {
            return RECIPE_TYPE;}
    }

    public void displaySearchCategories(){

   List<Recipe> categories= new ArrayList<>();
   for (int i=0 ; i< Constant.DEFAULT_SEARCH_CATEGORIES.length;i++){
       Recipe recipe= new Recipe();
       recipe.setTitle(Constant.DEFAULT_SEARCH_CATEGORIES[i]);
       recipe.setImageUrl(Constant.DEFAULT_SEARCH_CATEGORY_IMAGES[i]);
       recipe.setSocialUrl(-1);
       categories.add(recipe);

   }
        mRecipes = categories;
        notifyDataSetChanged();
    }





  public void displayLoading(){
        if(!isLoading()){
            Recipe recipe= new Recipe();
            recipe.setTitle("LOADING...");
            List<Recipe> loadingList= new ArrayList<>();
            loadingList.add(recipe);
            mRecipes=loadingList;
            notifyDataSetChanged();
        }

  }

  private boolean isLoading(){
        if(mRecipes!=null){
        if(mRecipes.size()>0){
            if(mRecipes.get(mRecipes.size()-1).getTitle().equals("LOADING...")){
            return true;
            }}

        }
        return false;
  }


  public Recipe getSelectedRecipe( int position){
        if(mRecipes!=null){
            if(mRecipes.size()>0){
            return mRecipes.get(position);}
        }
        return null;
  }



    @Override
    public int getItemCount() {
        if (mRecipes!=null){
            return mRecipes.size();
        }
      return 0;
    }
    public void setRecipes(List<Recipe> recipes){
        mRecipes=recipes;
        notifyDataSetChanged();
    }
}

[Norm Radder]

The print out shows that only ONE call was made to the Recipe class's constructor.    How many instances of Recipe are created?
If there are other instances of the Recipe class that were created without calling the constructor how were they created?  
Where does the data come from that fills the other instances?


Look in the displaySearchCategories() method.  It creates Recipes without using the  constructor shown in the posted code and without setting the id.
Change that method to make sure the id is being set.

[Giovanni Montano]

the problem should be that the bundle is not passed. in other words you are launching the class proper activity with a so called explicit intent without passing  a proper parameter. Please see how explicit intent are handled passing data via Bundle!

[Tim Holloway]

Norm Radder wrote:

help for such debugging code ,

I use print statements for debugging:

 
   //  Add following to constructor
   System.out.println("cons id="+id);  // show id in constructor
   ...
   // Add following to setRecipeId method
   System.out.println("set id="+id);   // show id in setRecipeId method
   

The printed lines will be in the logcat.

Why not just use the Android logging facility?

A) you can switch it on and off without deleting/inserting statements (many a module has been damaged in the process of changing print statements)

B) If it was worth noting at one time, there may be a future time when it's worth reporting again. Here, too, you can get that information just by flipping a (loglevel) switch.