如何在自定义视图中管理活动生命周期？

Question

Recently I was making a custom view in Android.

Like this:

the capture of the custom view before rotating

but when I rotate the phone screen, the app execute onPause onStop onDestroy then execute onCreate onStart onResume onMeasure onDraw , so it invalidate the view from the 0 of x coordinate.

Like this:

the capture of the custom view after rotating

I want to store the value of scroll X to SharePreferences , but I really don't know how to manage the Activity Lifecycle in the custom view.

Answer 1

Adding to swapnil's answer

sharedPrefernece or Bundle really does not matter. If you want to persist state even after app close use sharedPref otherwise bundle.

You probably need to use horizontal scrollView as your custom view might not fit in portrait mode . For enhanced user experience if you think portrait does not work well as user needs to scroll back and forth a lot you can also restrict orientation to landscape . In your manifest file add this attribute to activity node.

android:screenOrientation="landscape"

Answer 2

instead of SharedPreferences you can use function onSaveInstanceState() and onRestoreInstanceState()

onSavedInstanceState :

Called to retrieve per-instance state from an activity before being killed so that the state can be restored in onCreate(Bundle) or onRestoreInstanceState(Bundle) (the Bundle populated by this method will be passed to both).

This method is called before an activity may be killed so that when it comes back some time in the future it can restore its state. For example, if activity B is launched in front of activity A, and at some point activity A is killed to reclaim resources, activity A will have a chance to save the current state of its user interface via this method so that when the user returns to activity A, the state of the user interface can be restored via onCreate(Bundle) or onRestoreInstanceState(Bundle).

Do not confuse this method with activity lifecycle callbacks such as onPause(), which is always called when an activity is being placed in the background or on its way to destruction, or onStop() which is called before destruction. One example of when onPause() and onStop() is called and not this method is when a user navigates back from activity B to activity A: there is no need to call onSaveInstanceState(Bundle) on B because that particular instance will never be restored, so the system avoids calling it. An example when onPause() is called and not onSaveInstanceState(Bundle) is when activity B is launched in front of activity A: the system may avoid calling onSaveInstanceState(Bundle) on activity A if it isn't killed during the lifetime of B since the state of the user interface of A will stay intact.

The default implementation takes care of most of the UI per-instance state for you by calling onSaveInstanceState() on each view in the hierarchy that has an id, and by saving the id of the currently focused view (all of which is restored by the default implementation of onRestoreInstanceState(Bundle)). If you override this method to save additional information not captured by each individual view, you will likely want to call through to the default implementation, otherwise be prepared to save all of the state of each view yourself.

If called, this method will occur before onStop(). There are no guarantees about whether it will occur before or after onPause().

onRestoreInstanceState :

This method is called after onStart() when the activity is being re-initialized from a previously saved state, given here in savedInstanceState. Most implementations will simply use onCreate(Bundle) to restore their state, but it is sometimes convenient to do it here after all of the initialization has been done or to allow subclasses to decide whether to use your default implementation. The default implementation of this method performs a restore of any view state that had previously been frozen by onSaveInstanceState(Bundle).

You can find more examples at

Recreating Activity

How to use

Sample Example