The technical principles and design ideas of the ViewPager2 framework in the Java class library

ViewPager2 is a component in the Android Jetpack library. It provides a horizontal or vertical sliding view container to enable developers to easily create pages that can be slide left and right.This article will introduce the technical principles and design ideas of the ViewPager2 framework, and provide examples of Java code. 1. Technical principle: ViewPager2 is based on RecyclerView. It realizes the function similar to ViewPager by combining RecyclerView with page views such as Fragment or View.Here are some of the core principles of viewpager2: 1.1 Use RecyclerView: ViewPager2 Under the bottom layer of RecyclerView to manage and display the page, which enables it to support the features of many RecyclerViews, such as reuse views and data binding.ViewPager2 achieves the effect of left and right sliding by using LinearlayoutManager, and using GridLayoutManager can achieve a grid layout. 1.2 Data adapter: ViewPager2 needs to use a data adapter to provide page data.Developers need to create a adapter inherited from RecyclerView.adapter, and rewrite related methods, such as creating page views and binding data.The adapter can also support different page types, so that ViewPager2 can display pages with different styles or layouts. 1.3 Page switching: ViewPager2 supports multiple methods of page switching, including gesture sliding, clicking indicator and programming method.Developers can switch to a specific page using the setcurrentity method of ViewPager2 to switch to a specific page. It can also switch the event by monitoring the page through the AdDONPAGECHANGELISTENER method. 1.4 Page special effects: ViewPager2 provides some predetermined page special effects, such as fading, scaling, horizontal or vertical rotation, etc.Developers can set more cool switching effects by setting the special effects of the PageTransFormer. 2. Design ideas: The design idea of ViewPager2 mainly includes the following aspects: 2.1 Flexible page type: ViewPager2 supports different types of pages. Developers can return different page views in the adapter to achieve different styles or layout pages. 2.2 Data driver: One of the core principles of ViewPager2 is the data driver. Developers only need to provide page data without directly control the view.This data -driven approach makes the page better replication and scalability. 2.3 Customization of height: ViewPager2 provides rich methods and interfaces to meet the customization needs of developers, including page switching methods, page special effects, event monitoring, etc.Developers can customize the logic and effects of customized pages according to specific needs. 3. Java code example: Next, a simple Java code example is given to show how to use ViewPager2 to create a simple left and right sliding page application: // Use ViewPager2 in Activity ViewPager2 viewPager = findViewById(R.id.viewPager); MyPagerAdapter adapter = new MyPagerAdapter(getSupportFragmentManager()); viewPager.setAdapter(adapter); // Custom page surface adapter public class MyPagerAdapter extends FragmentStateAdapter { Private Static Final Int Num_pages = 3; // Number of pages public MyPagerAdapter(FragmentManager fragmentManager) { super(fragmentManager, getLifecycle()); } @Override public Fragment createFragment(int position) { return new MyPageFragment(); } @Override public int getItemCount() { return NUM_PAGES; } } // Page Fragment public class MyPageFragment extends Fragment { @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View rootView = inflater.inflate(R.layout.fragment_page, container, false); // Here you can initialize the page view and data binding return rootView; } } In the above code, we first define a ViewPager2 component in the layout file, and then set the page adapter through a custom Pageradapter.Pageradapter inherits from FragmentStateAdapter and returns the page Fragment as required.The initialization and data binding of the page view can be completed in the oncreateView method of Fragment. In summary, the ViewPager2 framework uses RecyclerView as the underlying implementation, and through the data adapter and page switching mechanism, a powerful and flexible page sliding function is realized.Developers can use ViewPager2 to build the application of various left and right sliding pages according to actual needs.