RecyclerView.Adapter 的 onCreateViewHolder 被调用了两次或更多次，多次

Question

我目前正在开发一个使用 RecyclerView 的应用程序。

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

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，但我知道每当回收项目时都会调用它。

不过我觉得onCreateViewHolder调用一次就够了

这是异常行为吗？如果是，如何解决？

Answer 1

这不是异常，而是很正常的行为。你不用担心。

确实是一个ViewHolder会被回收，不会再重新创建。

但是，需要多个 ViewHolders 才能在应用屏幕上显示多个项目。因此，将创建一定数量的 ViewHolder，并为此调用特定次数的 onCreateViewHolder。

每当数据重置为 ViewHolder 之一时，将无限调用 onBindViewHolder。

我用下面的测试应用程序检查了这个事实：

主要活动：

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);
    }
}

我的适配器：

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" />

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)之后只调用了onBindViewHolder。

Answer 2

您可以通过这段代码增加RecycledViewPool 的数量。默认情况下它有 5 个。

可以根据需要增加。

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

Answer 3

这里是 RecyclerView 稳定视图的稳定答案

下面这些行有助于在垂直方向上保持 recyclerview 中列表数据的一致性在我的垂直列表中只有 10 个项目，我不想再次重新绑定。每行都有无限的水平 RecyclerView 列表。

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

这两种方法都有助于不回收垂直视图。但是如果list太大的话会导致OOM错误，所以要小心实现。
```
Here 0 is viewType in Recyclerview adapter and 10 are the items count.

mRecyclerview.getRecycledViewPool().setMaxRecycledViews(0, 10);
mRecyclerview.setItemViewCacheSize(10);
```

Answer 4

取决于您的屏幕可以容纳多少行，但大多数情况下肯定多于 1 行。除非数组中只有一行作为参数传递给适配器。

我的应用适合 13 个纵向观看者。但有趣的是，我调用了 17 次 onCreateViewHolders。下面是一段日志语句：

...
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
...

我认为 onCreateViewHolder 会被调用 13 次，或最多 14 次，因为当我向下滚动到第 14 行时，第 1 行仍然部分可见。但是回收视图似乎需要一些时间才能开始重用现有的 viewHolder。在第 17 个 viewHolder 之后，不再创建新的 viewHolder。从那时起，现有的 viewHolders 将被回收。

RecyclerView.Adapter 的 onCreateViewHolder 被调用了两次或更多次，多次

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

android

android-viewholder

android-recyclerview