"Android Basics" Fragment Detailed introduction of Fragment

Fragment was introduced in Android 3.0 (API 11) to support a more dynamic, flexible UI on a large screen, such as on tablets and TVs. Fragment can be seen as nested activity, similar to Activitygroup, but the cost is certainly not activitygroup so large, each fragment manages a view,fragment each other independent, Has its own life cycle, which is the life cycle of the activity. Fragment can be used to solve problems with screen adaptation and dynamic View creation.

A fragment is always embedded in an activity and is a modular view whose life cycle is influenced by the activity life cycle it embeds. For example, activity into the paused state, so many attached to the activity of the fragment will enter the paused state, when the activity is destroyed, all the fragment attached to the activity will be destroyed. Then when the activty into the running state Onresume, you can independently manage each fragment, you can add a fragment, you can remove a fragment. When you perform a fragment transaction (created and displayed), you can put this fragment on the fragment fallback stack, which records all the fragment transactions that you have performed. When you click the Back button, you can take a fragment from the fragment stack to display it.

The life cycle of fragment:

If you are aware of the life cycle of the activity it is easy to understand the fragment life cycle, there are many callback methods like activity lifecycle functions in fragment, which are called by the Android system. The official Fragment life cycle chart is as follows:

• Oncreat ():
  The system calls this function to create fragment, which is used to create resources used throughout the fragment cycle, such as those used in paused, stoped, or resumed methods.
• Oncreateview ():
  When fragment needs to draw the user interface for the first time, the system calls this function to finish drawing the UI, you must return a view in this function, the view is the root view of fragment, and returns null if you do not want to fragment display the view.
• OnPause ():
  When you leave fragment, the system calls this function first, in which you need to save the user's state like the work done in the activity's OnPause method.

In general, an application needs to rewrite at least three functions to complete your application logic.

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"Android Basics" Fragment Detailed introduction of Fragment