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

Depends on how many rows your screen can fit, but it is definitely more that 1 most of the time. Unless there is only one row in the array that you pass to your adapter as an argument.

My app fits 13 viewholders in portrait orientation. But interestingly, I had onCreateViewHolders called 17 times. Below is a piece of the log statements:

...
D/NerdLauncherActivity: onCreateViewHolder 14
D/NerdLauncherActivity: onBindViewHolder 14
D/NerdLauncherActivity: onCreateViewHolder 15
D/NerdLauncherActivity: onBindViewHolder 15
D/NerdLauncherActivity: onCreateViewHolder 16
D/NerdLauncherActivity: onBindViewHolder 16
D/NerdLauncherActivity: onCreateViewHolder 17
D/NerdLauncherActivity: onBindViewHolder 17
D/NerdLauncherActivity: onBindViewHolder 18
D/NerdLauncherActivity: onBindViewHolder 19
D/NerdLauncherActivity: onBindViewHolder 20
...

I thought the onCreateViewHolder would be called exactly 13 times, or at most 14 times, since when I scroll down to the 14th row, the 1st row is still partially visible. But it seems that it takes some time for the recycle view to start reusing existing viewHolders. After the 17th viewHolder, no new viewHolder is created. The existing viewHolders are being recycler from then on.

Answer 2

Here is a stable answer to stable Views for RecyclerView

These below line help to consistent list data in recyclerview vertically In my vertical list having only 10 items which i don't want to rebind again. Each row having infinite horizontal RecyclerView list.

1. mRecyclerview.getRecycledViewPool().setMaxRecycledViews(int viewtype,int itemsCount)

2. mRecyclerview.setItemViewCacheSize(int itemsCount)

   Both method helps not to recycle vertical views. But if list is too large then it will cause you OOM error, So be carefull to implement it.

   Here 0 is viewType in Recyclerview adapter and 10 are the items count.
   
   mRecyclerview.getRecycledViewPool().setMaxRecycledViews(0, 10);
   mRecyclerview.setItemViewCacheSize(10);
   

Answer 3

You can increase the RecycledViewPool count by this code. By default it have 5.

you can increase as per your need.

recyclerView.getRecycledViewPool().setMaxRecycledViews(0,50);//0 - your view type

Answer 4

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).