1# PageAbility Lifecycle 2 3 4The PageAbility lifecycle defines all states of a PageAbility, such as **INACTIVE**, **ACTIVE**, and **BACKGROUND**. The figure below shows the lifecycle state transition. 5 6**Figure 1** PageAbility lifecycle 7 8 9 10**Table 1** PageAbility lifecycle states 11 12| State| Description| 13| -------- | -------- | 14| UNINITIALIZED | The PageAbility is not initialized. This is a temporary state, from which a PageAbility changes directly to the **INITIAL** state upon its creation.| 15| INITIAL | The PageAbility is initialized but not running. The PageAbility enters the **INACTIVE** state after it is started.| 16| INACTIVE | The PageAbility is visible but does not gain focus.| 17| ACTIVE | The PageAbility runs in the foreground and has focus.| 18| BACKGROUND | The PageAbility runs in the background. After being re-activated, the PageAbility enters the **ACTIVE** state. After being destroyed, it enters the **INITIAL** state.| 19 20 21You can override the lifecycle callbacks (as described in the table below) in **app.js** or **app.ets**. 22 23**Table 2** PageAbility lifecycle callbacks 24 25| API| Description| 26| -------- | -------- | 27| onCreate() | Called when the ability is created for the first time. You can initialize the application in this callback.| 28| onDestroy() | Called when the ability is destroyed. In this callback, you can make preparations for application exit, such as recycling resources and clearing the cache.| 29| onActive() | Called when the ability is switched to the foreground and gains focus.| 30| onInactive() | Called when the ability loses focus. An ability loses focus when it is about to enter the background state.| 31| onShow() | Called when the ability is switched from the background to the foreground. In this case, the ability is visible to users.| 32| onHide() | Called when the ability is switched from the foreground to the background. In this case, the ability is invisible to users.| 33 34 35The following figure shows the relationship between lifecycle callbacks and lifecycle states of the PageAbility. 36 37Figure 2 Relationship between lifecycle callbacks and lifecycle states 38 39 40 41 42> **NOTE** 43> 44> - The PageAbility lifecycle callbacks are synchronous. 45> - The **app.js** file provides only the **onCreate** and **onDestroy** callbacks, and the **app.ets** file provides the full lifecycle callbacks. 46
