RecyclerView.Adapter的onCreateViewHolder被调用两次或多次，多次 [英] onCreateViewHolder of RecyclerView.Adapter is called twice or more, multiple times

问题描述

我目前正在开发一个使用RecyclerView的应用程序.

I'm currently developing an application which uses RecyclerView.

在查看LogCat时，我注意到 onCreateViewHolder 在实例化后被调用了两次.

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

onBindViewHolder也被调用了两次，尽管我知道每当项目被回收时都会被调用.

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

但是我认为对于onCreateViewHolder来说，一次调用就足够了.

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

这是异常行为吗?如果是这样，如何解决?

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

推荐答案

这不是异常现象，而是正常现象.您不必担心.

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

确实，ViewHolder将被回收并且不会再次重新创建.

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

但是，需要多个ViewHolders 才能在应用程序的屏幕上显示多个项目.因此，将创建一定数量的ViewHolders，并为此调用onCreateViewHolder.

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.

每当将数据重置为ViewHolders之一时，就会无限调用onBindViewHolder.

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

我通过如下测试应用程序检查了这个事实:

I examined this fact with test application like below:

MainActivity:

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:

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:

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:

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" />

结果:

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)

如您所见，在onCreateViewHolder (15)之后仅调用了onBindViewHolder.

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

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