angular有一套生命周期事件:
https://angular.cn/guide/lifecycle-hooks
ionic也有，其更贴近app交互需求，在开发时应尽量使用ionic这套:
| Page Event | Returns | Description |
|---|---|---|
ionViewDidLoad |
void | Runs when the page has loaded. This event only happens once per page being created. If a page leaves but is cached, then this event will not fire again on a subsequent viewing. TheionViewDidLoad event is good place to put your setup code for the page. |
ionViewWillEnter |
void | Runs when the page is about to enter and become the active page. |
ionViewDidEnter |
void | Runs when the page has fully entered and is now the active page. This event will fire, whether it was the first load or a cached page. |
ionViewWillLeave |
void | Runs when the page is about to leave and no longer be the active page. |
ionViewDidLeave |
void | Runs when the page has finished leaving and is no longer the active page. |
ionViewWillUnload |
void | Runs when the page is about to be destroyed and have its elements removed. |
ionViewCanEnter |
boolean/Promise<void> | Runs before the view can enter. This can be used as a sort of “guard” in authenticated views where you need to check permissions before the view can enter |
ionViewCanLeave |
boolean/Promise<void> | Runs before the view can leave. This can be used as a sort of “guard” in authenticated views where you need to check permissions before the view can leave |
