为什么 FragmentStateAdapter 在 ViewPager2 中不起作用？

Question

Android Studio 3.6

我想在我的活动中使用 ViewPager2 中的 2 个片段。

这是我的活动：

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.viewpager2.widget.ViewPager2;
public class QRBluetoothSwipeActivity extends AppCompatActivity {
    private ViewPager2 myViewPager2;
    private ViewPagerFragmentAdapter myAdapter;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        // Make sure this is before calling super.onCreate
        setTheme(R.style.AppTheme); // show splash screen
        super.onCreate(savedInstanceState);
        setContentView(R.layout.qr_bluetooth_swipe_activity);
        init();
    }

    private void init() {
        myAdapter = new ViewPagerFragmentAdapter(getSupportFragmentManager());
        myAdapter.addFragment(new BluetoothPageFragment());
        myAdapter.addFragment(new QrPageFragment());
        myViewPager2.setOrientation(ViewPager2.ORIENTATION_VERTICAL);
        myViewPager2.setAdapter(myAdapter);
    }

}

这里 ViewPagerFragmentAdapter

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.viewpager2.adapter.FragmentStateAdapter;

import java.util.ArrayList;

public class ViewPagerFragmentAdapter  extends FragmentStateAdapter {

    private ArrayList<Fragment> arrayList = new ArrayList<>();

    public ViewPagerFragmentAdapter(@NonNull FragmentManager fragmentManager) {
        super(fragmentManager);
    }

    @NonNull
    @Override
    public Fragment getItem(int position) {
        return arrayList.get(position);
    }

    public void addFragment(Fragment fragment) {
        arrayList.add(fragment);
    }

    @Override
    public int getItemCount() {
        return arrayList.size();
    }
}

但我得到编译错误：

ViewPagerFragmentAdapter is not abstract and does not override abstract method createFragment(int) in FragmentStateAdapter

我该如何解决这个问题并在ViewPager2中使用FRAGMENTS ？

谢谢

Answer 1

ViewPager中的FragmentStateAdapter与ViewPager2中的稍有不同，如下所示：

• 代替实现getCount() ，实现getItemCount()

• 代替实现getItem(int position) ，实现createFragment(int position)

• 构造函数签名通过添加Lifecycle参数而有所不同，该参数也应包含在 super 中

所以用下面的替换你的ViewPagerFragmentAdapter

import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.lifecycle.Lifecycle;
import androidx.viewpager2.adapter.FragmentStateAdapter;

import java.util.ArrayList;


public class ViewPagerFragmentAdapter extends FragmentStateAdapter {

    private ArrayList<Fragment> arrayList = new ArrayList<>();

    public ViewPagerFragmentAdapter(@NonNull FragmentManager fragmentManager, @NonNull Lifecycle lifecycle) {
        super(fragmentManager, lifecycle);
    }


    public void addFragment(Fragment fragment) {
        arrayList.add(fragment);
    }

    @Override
    public int getItemCount() {
        return arrayList.size();
    }

    @NonNull
    @Override
    public Fragment createFragment(int position) {
        // return your fragment that corresponds to this 'position'
        return arrayList.get(position);
    }

}

还要确保导入/扩展 ViewPager2 的正确适配器

import androidx.viewpager2.adapter.FragmentStateAdapter;

希望这会有所帮助，并很高兴获得更多说明