Interpret the technical principle of the ViewPager2 framework in the Java library

ViewPager2 is a component in AndReid Support Library, which provides developers with the function of creating a sliding view page in the application.Compared with the previous version of ViewPager, ViewPager2 has some improvements and changes in technical principles. ViewPager2 is implemented by the layout, loading and switching of the view page as three independent components.First, developers need to define the layout of each page, which can be completed by creating a XML layout file.Then, you need to create an Adapter class to be responsible for loading and management pages.The Adapter class needs to implement the ViewPageradapter or FragmentStateadapter interface, which depends on the content type used in ViewPager2.In the Adapter class, developers need to rewrite the GetItemCount method to specify the number of view pages and create a view of each page through the CreateFragment or CreateView method.Finally, in the Java code, you can use the ViewPager2 category to initialize the ViewPager2 instance and associate it with Adapter. In addition to the above basic steps, ViewPager2 also provides some other technical principles and functions.One of them is to support horizontal and vertical sliding.By setting the Orientation property to Horizontal or Vertical, developers can freely select the sliding direction of ViewPager2.Another important feature is page switching animation.ViewPager2 allows developers to set the switching effect between the defined page by setting the PageTransFormer.In addition, ViewPager2 also provides some other methods and callbacks to handle user interaction and event processing. The following is a simple Java code example, which shows how to use ViewPager2 in the application: // Define the xml file of the page layout // fragment_my_page.xml <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <TextView android:id="@+id/page_title" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Page Title" android:textSize="24sp" android:layout_gravity="center_horizontal"/> <ImageView android:id="@+id/page_image" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_gravity="center_horizontal" android:src="@drawable/image"/> </LinearLayout> // Define customized PageAdapter classes public class MyPageAdapter extends FragmentStateAdapter { public MyPageAdapter(FragmentActivity fragmentActivity) { super(fragmentActivity); } @NonNull @Override public Fragment createFragment(int position) { return new MyFragment(); } @Override public int getItemCount() { return 3; } } // Define the customized Fragment class public class MyFragment extends Fragment { @Nullable @Override public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { View view = inflater.inflate(R.layout.fragment_my_page, container, false); TextView pageTitle = view.findViewById(R.id.page_title); ImageView pageImage = view.findViewById(R.id.page_image); // Here you can set different content according to the page location return view; } } // Initialize ViewPager2 in the Java code ViewPager2 viewPager2 = findViewById(R.id.view_pager); MyPageAdapter adapter = new MyPageAdapter(this); viewPager2.setAdapter(adapter); The above example code shows how to use ViewPager2 to create a simple sliding page in the application, which contains some basic elements (such as titles and pictures).By customized PageAdapter and Fragment, multiple different pages can be achieved.In actual development, developers can expand and customize according to their needs and business logic.