Detailed explanation of the technical principles of the ViewPager2 framework in the Java class library
The ViewPager2 framework is a page switching library officially launched by Android, providing developers with a simple and powerful view navigation solution.It is an upgraded version based on ViewPager, supporting more functions and characteristics.This article will explain the technical principles of the ViewPager2 framework in detail and provide some Java code examples.
1. Description ViewPager2 framework
The ViewPager2 framework is a library that can be switched on the sliding page switching in Android applications.It can be used to build pages with horizontal or vertical sliding, such as picture browser, guidance page, tab layout, etc.ViewPager2 provides more scalability and support for specific user cases than the old version of ViewPager.
2. Technical principles
The core technical principles of the ViewPager2 framework are as follows:
2.1 RecyclerView as a container
ViewPager2 uses RecyclerView as its internal container.RecyclerView is an efficient list view container provided by the Android framework. It can handle a lot of data rolling and reusable views, and has a flexible layout manager.
2.2 adapter and viewholder
Similar to ViewPager, ViewPager2 also needs a Adapter to provide data, and use ViewHolder to display the content of each page.Adapter is responsible for providing the number and actual view of the page, and Viewholder is responsible for binding the view to the data.
2.3 LinearLayoutManager
ViewPager2 uses LinearlayoutManager as a layout manager.You can determine the sliding direction of the page by setting the direction (horizontal or vertical) of the layout manager.
2.4 ItemDecoration
You can use the ItemDecorant class to add a differential effect such as ViewPager2.
2.5 SnapHelper
Snaphelper is an auxiliary class for alignment page.For example, you can use Pagersnaphelper to ensure that each page is aligned after sliding.
2.6 Transformations (converter)
The ViewPager2 framework introduces a Transformations class. Developers can use this class to apply various visual effects, such as fading into fading and rotating.
3. Java code example
Here are a simple Java code example to demonstrate how to use the ViewPager2 framework to create a basic horizontal sliding page layout.
import androidx.appcompat.app.AppCompatActivity;
import androidx.viewpager2.widget.ViewPager2;
public class MainActivity extends AppCompatActivity {
private ViewPager2 viewPager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
viewPager = findViewById(R.id.viewPager);
MyAdapter adapter = new MyAdapter();
viewPager.setAdapter(adapter);
}
}
class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
@NonNull
@Override
public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_layout, parent, false);
return new MyViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
// Bind data to view
}
@Override
public int getItemCount() {
Return 3; // Number of pages
}
class MyViewHolder extends RecyclerView.ViewHolder {
public MyViewHolder(@NonNull View itemView) {
super(itemView);
}
}
}
In the above code, first create a ViewPager2 instance in the Mainactivity, and use a custom adapter MyAdapter to set the adapter.Then in MyAdapter, create a customized ViewHolder by rewriting the oncreateViewHolder method, and bind the data to the view in the OnBindViewHolder method.
Summarize
This article explains the technical principles of the ViewPager2 framework and provides a simple Java code example.The ViewPager2 framework uses RecyclerView as an internal container, with adapter and ViewHolder and other components to achieve a powerful view navigation function.Developers can use ViewPager2 to build a sliding page function based on their own needs to achieve a rich user interaction experience.
