ViewPage2

繼上一篇寫的Fragment，今天我們與ViewPage2搭配使用。使用ViewPage我們可以達成左右滑動換頁的效果，ViewPage就如同一個容器，可以裝下多個Fragment，透過手勢動作完成Fragment切換。

建立Fragment

建立以下三個Fragment：

• fragment_a.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".FragmentA">

    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:textSize="50dp"
        android:text="FragmentA" />

</FrameLayout>

• fragment_b.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".FragmentB">

    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:textSize="50dp"
        android:text="FragmentB" />

</FrameLayout>

• fragment_c.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".FragmentC">

    <!-- TODO: Update blank fragment layout -->
    <TextView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:textSize="50dp"
        android:text="FragmentC" />

</FrameLayout>

於activity_main中加入ViewPage2

加入ViewPage2布局容器

• activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/viewPage2"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

建立ViewPageAdapter

• ViewPageAdapter.java
  在createFragment中，透過position使用switch切換Fragment。

public class ViewPageAdapter extends FragmentStateAdapter {

    public ViewPageAdapter(@NonNull FragmentActivity fragmentActivity) {
        super(fragmentActivity);
    }

    @NonNull
    @Override
    public Fragment createFragment(int position) {
        //切換Fragment
        switch(position){
            case 0:
                return new FragmentA();
            case 1:
                return new FragmentB();
            default:
                return new FragmentC();
        }
    }

    @Override
    public int getItemCount() {
        //設定頁數
        return 3;
    }
}

於MainActivity綁定Adapter

• MainActivity.java

public class MainActivity extends AppCompatActivity {
    private ViewPager2 viewPager2;
    private ViewPageAdapter viewPageAdapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //元件綁定
        viewPager2 = findViewById(R.id.viewPage2);
        //設定ViewPage的Adapter
        viewPageAdapter = new ViewPageAdapter(this);
        viewPager2.setAdapter(viewPageAdapter);
    }
}