Research on Java Library Library Library Library Technology Principles of Android Support Library Fragment
Research on Java Library Library Library Library Technology Principles of Android Support Library Fragment
Abstract: Android has added the Fragment framework to simplify the development of applications.This article will study the technical principles of the Java class library of the Fragment framework and provide the corresponding Java code example.
introduction:
Fragment is a reusable component on the Android platform to build a flexible and interactive user interface.It can be embedded in the Activity, so that one Activity can contain multiple fragments, thereby realizing modularity and dynamicity.In order to support a broader Android version, Google introduced Android Support Library Fragment framework, which allows developers to use the Fragment features on the old version of the old version of the old version through a downward compatibility method.This article will study the technical principles and code examples of the Java -class library of this framework in detail.
1. Fragment framework overview
Fragment is a combination of Behavior and User interface (UI), similar to a module of Activity.Each interface in the Android application is composed of one or more frames. They share the life cycle of Activity and can be added, deleted and replaced during runtime.The Fragment framework provides some APIs to manage the life cycle, interface and interaction of Fragment.
Second, an important category of Android Support Library Fragment framework
1. Fragment: Fragment class is a base class of all Fragment classes. Developers can create custom Fragment by extending this type.It provides many methods for managing the life cycle and interface for managing Fragment, such as onCreate (), onCreateView (), and onDestroy ().
The following is a simple example:
public class MyFragment extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// In this method, create and return the Fragment interface view
return inflater.inflate(R.layout.fragment_layout, container, false);
}
}
2. FragmentManager: The FragmentManager class is used to manage the life cycle and interaction of Fragment.Through FragmentManager, developers can add, delete and replace Fragment, and perform operations such as transaction.The following is an example of adding Fragment:
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
MyFragment fragment = new MyFragment();
fragmentTransaction.add(R.id.fragment_container, fragment);
fragmentTransaction.commit();
3. FragmentPageradapter: FragmentPageradapter class is used to display multiple Fragment in ViewPager.Developers need to inherit this category and rewrite the getItem () method to return the Fragment instance of the specified position.The following is a simple example:
public class MyFragmentPagerAdapter extends FragmentPagerAdapter {
private final int NUM_PAGES = 3;
public MyFragmentPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
// Return different Fragment examples according to the location
switch (position) {
case 0:
return new Fragment1();
case 1:
return new Fragment2();
case 2:
return new Fragment3();
default:
return null;
}
}
@Override
public int getCount() {
// Return to Fragment
return NUM_PAGES;
}
}
Third, the working principle of Android support library frame
The Android Support Library Fragment framework is introduced to the new version of Fragment features in the early version of Android.It manages the life cycle of the Fragment based on the life cycle of Activity and embeds the frame into the root layout of the Activity.This framework also provides Fragment's backbacking stack to support the operation of the back button.At the bottom, it maintains a FragmentManager to manage the creation, destruction and loading of Fragment.
When the life cycle of Activity changes, the FragmentManager manages the life cycle of Fragment accordingly.For example, when Activity enters the background, FragmentManager calls the onpause () method of Fragment.In addition, FragmentManager is also responsible for embedding Fragment into the view level of Activity.Developers can use FragmentManager API to add, delete and replace Fragment.
The Android Support Library Fragment framework also provides the FragmentPageradapter class to simplify the association between ViewPager and Fragment.Developers only need to implement the GetItem () and GetCount () methods, and they can easily add multiple Fragment to the ViewPager for sliding and switching.
in conclusion:
This article studies the Java -class library technical principles of Android Support Library Fragment framework, and provides related Java code examples.The Fragment framework simplifies the development of Android applications, providing a way of decoupling interface and behavior, making the application more modular and easy to maintain.By learning and using the Fragment framework, developers can build a wealth of dynamic user interface to enhance the user experience.
