onCreateViewHolder of RecyclerView.Adapter is called twice or more, multiple times

Question

I'm currently developing an application which uses RecyclerView.

On reviewing LogCat I noticed that onCreateViewHolder was called twice after it was instantiated.

09-22 05:22:55.209 V/Adapter﹕ Construct 09-22 05:22:55.213 V/Adapter﹕ onCreateViewHolder 09-22 05:22:55.224 V/Adapter﹕ onBindViewHolder 09-22 05:22:55.240 V/Adapter﹕ onCreateViewHolder 09-22 05:22:55.247 V/Adapter﹕ onBindViewHolder 

Also onBindViewHolder was called twice though I know it is called whenever the items are recycled.

But I think for onCreateViewHolder it is sufficient to be called once.

Is this abnormal behavior? If so, how can it be fixed?

Answer 1

It's not abnormal but quite normal behavior. You don't have to worry.

It is true that a ViewHolder will be recycled and won't be re-created again.

However, multiple ViewHolders are needed to display multiple items on the app's screen. So there will a certain numbers of ViewHolders are created and for that onCreateViewHolder is called a certain times.

And onBindViewHolder will be called infinitly whenever data is reset to one of ViewHolders.

I examined this fact with test application like below:

MainActivity:

public class MainActivity extends AppCompatActivity {     private static final String[] DATASET = new String[]{             "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m",             "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z",     };      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_view);         recyclerView.setHasFixedSize(true);          LinearLayoutManager layoutManager = new LinearLayoutManager(this);         recyclerView.setLayoutManager(layoutManager);          MyAdapter myAdapter = new MyAdapter(DATASET);         recyclerView.setAdapter(myAdapter);     } } 

MyAdapter:

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {     private static final String LOG_TAG = "RecyclerViewAdapter";     private String[] dataset;      private int counterOnCreateViewHolder = 0;     private int counterOnBindViewHolder = 0;      public MyAdapter(String[] dataset) {         Log.d(LOG_TAG, "Construct");         this.dataset = dataset;     }      public static class ViewHolder extends RecyclerView.ViewHolder {         public TextView textView;         public ViewHolder(TextView textView) {             super(textView);             this.textView = textView;         }     }      @Override     public MyAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {         Log.d(LOG_TAG, "onCreateViewHolder (" + ++counterOnCreateViewHolder + ")");         View view = LayoutInflater.from(parent.getContext())                 .inflate(R.layout.adapter_textview, parent, false);          ViewHolder viewHolder = new ViewHolder((TextView) view);         return viewHolder;     }      @Override     public void onBindViewHolder(ViewHolder holder, int position) {         Log.d(LOG_TAG, "onBindViewHolder (" + ++counterOnBindViewHolder + ")");         holder.textView.setText(dataset[position]);     }      @Override     public int getItemCount() {         // Log.d(LOG_TAG, "getItemCount");         return dataset.length;     } } 

layout/activity_main.xml:

<android.support.v7.widget.RecyclerView     xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:scrollbars="vertical"     android:id="@+id/recycler_view" /> 

layout/adapter_textview.xml:

<TextView     xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:id="@+id/adapter_textview"     android:textSize="30sp" /> 

Result:

09-22 06:03:04.166 D/RecyclerViewAdapter﹕ Construct 09-22 06:03:05.179 D/RecyclerViewAdapter﹕ onCreateViewHolder (1) 09-22 06:03:05.183 D/RecyclerViewAdapter﹕ onBindViewHolder (1) 09-22 06:03:05.190 D/RecyclerViewAdapter﹕ onCreateViewHolder (2) 09-22 06:03:05.192 D/RecyclerViewAdapter﹕ onBindViewHolder (2) 09-22 06:03:05.192 D/RecyclerViewAdapter﹕ onCreateViewHolder (3) 09-22 06:03:05.194 D/RecyclerViewAdapter﹕ onBindViewHolder (3) 09-22 06:03:05.195 D/RecyclerViewAdapter﹕ onCreateViewHolder (4) 09-22 06:03:05.197 D/RecyclerViewAdapter﹕ onBindViewHolder (4) 09-22 06:03:05.198 D/RecyclerViewAdapter﹕ onCreateViewHolder (5) 09-22 06:03:05.199 D/RecyclerViewAdapter﹕ onBindViewHolder (5) 09-22 06:03:05.200 D/RecyclerViewAdapter﹕ onCreateViewHolder (6) 09-22 06:03:05.202 D/RecyclerViewAdapter﹕ onBindViewHolder (6) 09-22 06:03:05.203 D/RecyclerViewAdapter﹕ onCreateViewHolder (7) 09-22 06:03:05.204 D/RecyclerViewAdapter﹕ onBindViewHolder (7) 09-22 06:03:05.206 D/RecyclerViewAdapter﹕ onCreateViewHolder (8) 09-22 06:03:05.207 D/RecyclerViewAdapter﹕ onBindViewHolder (8) 09-22 06:03:05.209 D/RecyclerViewAdapter﹕ onCreateViewHolder (9) 09-22 06:03:05.211 D/RecyclerViewAdapter﹕ onBindViewHolder (9) 09-22 06:03:05.212 D/RecyclerViewAdapter﹕ onCreateViewHolder (10) 09-22 06:03:05.213 D/RecyclerViewAdapter﹕ onBindViewHolder (10) 09-22 06:03:05.215 D/RecyclerViewAdapter﹕ onCreateViewHolder (11) 09-22 06:03:05.217 D/RecyclerViewAdapter﹕ onBindViewHolder (11) 09-22 06:03:05.218 D/RecyclerViewAdapter﹕ onCreateViewHolder (12) 09-22 06:03:05.220 D/RecyclerViewAdapter﹕ onBindViewHolder (12) 09-22 06:03:55.048 D/RecyclerViewAdapter﹕ onCreateViewHolder (13) 09-22 06:03:55.050 D/RecyclerViewAdapter﹕ onBindViewHolder (13) 09-22 06:03:55.228 D/RecyclerViewAdapter﹕ onCreateViewHolder (14) 09-22 06:03:55.229 D/RecyclerViewAdapter﹕ onBindViewHolder (14) 09-22 06:03:55.230 D/RecyclerViewAdapter﹕ onCreateViewHolder (15) 09-22 06:03:55.231 D/RecyclerViewAdapter﹕ onBindViewHolder (15) 09-22 06:03:55.232 D/RecyclerViewAdapter﹕ onBindViewHolder (16) 09-22 06:03:55.232 D/RecyclerViewAdapter﹕ onBindViewHolder (17) 09-22 06:03:55.260 D/RecyclerViewAdapter﹕ onBindViewHolder (18) 09-22 06:03:55.276 D/RecyclerViewAdapter﹕ onBindViewHolder (19) 09-22 06:03:55.296 D/RecyclerViewAdapter﹕ onBindViewHolder (20) 09-22 06:03:55.310 D/RecyclerViewAdapter﹕ onBindViewHolder (21) 

As you can see, only onBindViewHolder was called after onCreateViewHolder (15).