# LifeCycle
Fragment lifecycle is similar to Activity lifecycle
* Lifecycle callbacks define how Fragment behaves in each state
* States
* Active(or Resumed)
* Paused
* Stopped
| **Activity state** | **Fragment callbacks triggered** | **Fragment lifecycle** |
| ------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------- |
| **Created** | | Fragment is added and its layout is inflated |
| **Started** | | Fragment is active and visible |
| **Resumed** | | Fragment is active and ready for user interaction |
| **Paused** | | Fragment is paused because Activity is paused |
| **Stopped** | | Fragment is stopped and no longer visible |
| **Destroyed** | | Fragment is destroyed |
**@Override** [**`onCreate(Bundle savedInstanceState)`**](https://developer.android.com/reference/android/app/Fragment.html#onCreate\(android.os.Bundle\))**:**
* System calls `onCreate()` when the Fragment is created
* Initialize Fragment components and variables (preserved if the Fragment is paused and resumed)
* Always include `super.onCreate(savedInstanceState)` in lifecycle callbacks
**@Override** [**`onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)`**](https://developer.android.com/reference/android/app/Fragment.html#onCreateView\(android.view.LayoutInflater,%20android.view.ViewGroup,%20android.os.Bundle\))**:**
* Inflate XML layout—required if Fragment has a UI
* System calls this method to make Fragment visible
* Must return the root [`View`](https://developer.android.com/reference/android/view/View.html) of Fragment layout\
or null if the Fragment does not have a UI
| More Callbacks | |
| ------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------- |
| [**`onAttach()`**](https://developer.android.com/reference/android/app/Fragment.html#onAttach\(android.content.Context\)) | Called when Fragment is first attached to Activity |
| [**`onPause()`**](https://developer.android.com/reference/android/app/Fragment.html#onPause\(\)) | Called when Activity is paused |
| [**`onResume()`**](https://developer.android.com/reference/android/app/Fragment.html#onResume\(\)) | Called by Activity to resume a visible Fragment |
| [**`onActivityCreated()`**](https://developer.android.com/reference/android/app/Fragment.html#onActivityCreated\(android.os.Bundle\)) | Called when Activity `onCreate()` method has returned |
| [**`onDestroyView()`**](https://developer.android.com/reference/android/app/Fragment.html#onDestroyView\(\)) | Called when View previously created by `onCreateView()` is detached from Fragment |
[**`onActivityCreated()`**](https://developer.android.com/reference/android/app/Fragment.html#onActivityCreated\(android.os.Bundle\))**:** Called when the Activity onCreate() method has returned
* Called after [`onCreateView()`](https://developer.android.com/reference/android/app/Fragment.html#onCreateView\(android.view.LayoutInflater,%20android.view.ViewGroup,%20android.os.Bundle\)) and before [`onViewStateRestored()`](https://developer.android.com/reference/android/app/Fragment.html#onViewStateRestored\(android.os.Bundle\))
* Retrieve views or restore state
* Use [`setRetainInstance()`](https://developer.android.com/reference/android/app/Fragment.html#setRetainInstance\(boolean\)) to keep Fragment instance when Activity is recreated
Use [`onDestroyView()`](https://developer.android.com/reference/android/app/Fragment.html#onDestroyView\(\)) to perform action after Fragment is no longer visible
* Called after[`onStop()`](https://developer.android.com/reference/android/app/Fragment.html#onStop\(\)) and before [`onDestroy()`](https://developer.android.com/reference/android/app/Fragment.html#onDestroy\(\))
* View that was created in `onCreateView()` is destroyed
* A new View is created next time Fragment needs to be displayed
### Activity Context
When Fragment is active or resumed:
* Use [`getActivity()`](https://developer.android.com/reference/android/app/Fragment.html#getActivity\(\)) to get the[`Activity`](https://developer.android.com/reference/android/app/Activity.html) that started the fragment
* Find a View in the Activity layout:
```java
View listView = getActivity().findViewById(R.id.list);
```
Get Fragment by calling [`findFragmentById()`](https://developer.android.com/reference/android/app/FragmentManager.html#findFragmentById\(int\)) on `FragmentManager`:
```java
ExampleFragment fragment = (ExampleFragment)
getFragmentManager().findFragmentById(R.id.example_fragment);
// ...
mData = fragment.getSomeData();
```
Add Fragment to back stack: [`addToBackStack(null)`](https://developer.android.com/reference/android/app/FragmentTransaction.html#addToBackStack\(java.lang.String\))
* Host `Activity` maintains back stack even after `Fragment` is removed
* Allows navigation with Back button
```java
fragmentTransaction.add(R.id.fragment_container, fragment);
fragmentTransaction.addToBackStack(null);
fragmentTransaction.commit();
```