如何在自定义视图中管理活动生命周期？

Question

最近我在 Android 中制作自定义视图。

像这样：

the capture of the custom view before rotating

但是当我旋转手机屏幕时，应用程序执行onPauseonStoponDestroy然后执行onCreateonStartonResumeonMeasureonDraw，所以它使从0的视图无效x 坐标。

像这样：

the capture of the custom view after rotating

我想把scroll X的值存储到SharePreferences，但是我真的不知道怎么在自定义视图中管理Activity Lifecycle。

Answer 1

添加到swapnil的答案

sharedPrefernece 或 Bundle 真的无关紧要。如果您想在应用关闭后保持状态，请使用 sharedPref 否则捆绑。

您可能需要使用horizontal scrollView，因为您的自定义视图可能不适合portrait mode。为了增强用户体验，如果您认为纵向效果不佳，因为用户需要来回滚动很多，您还可以将方向限制为 landscape。 在您的 manifest 文件中将此属性添加到活动节点。

android:screenOrientation="landscape"

Answer 2

您可以使用函数onSaveInstanceState() 和onRestoreInstanceState() 而不是SharedPreferences

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).

您可以在以下位置找到更多示例

Recreating Activity

How to use

Sample Example