# ViewTreeObserver.OnWindowFocusChangeListener

Added in[API level 18](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels)

# OnWindowFocusChangeListener

*** ** * ** ***

Kotlin\|[Java](https://developer.android.com/reference/android/view/ViewTreeObserver.OnWindowFocusChangeListener "View this page in Java")  

```
interface OnWindowFocusChangeListener
```

|------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| [android.view.ViewTreeObserver.OnWindowFocusChangeListener](https://developer.android.com/reference/kotlin/android/view/ViewTreeObserver.OnWindowFocusChangeListener#) |

Interface definition for a callback to be invoked when the view hierarchy's window focus state changes.

## Summary

|                                                                                                                                                                                                                Public methods                                                                                                                                                                                                                 ||
|--------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| abstract[Unit](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html) | [onWindowFocusChanged](https://developer.android.com/reference/kotlin/android/view/ViewTreeObserver.OnWindowFocusChangeListener#onWindowFocusChanged(kotlin.Boolean))`(`hasFocus:` `[Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html)`)` Callback method to be invoked when the window focus changes in the view tree. |

## Public methods

### onWindowFocusChanged

Added in[API level 18](https://developer.android.com/guide/topics/manifest/uses-sdk-element.html#ApiLevels)  

```
abstract fun onWindowFocusChanged(hasFocus: Boolean): Unit
```

Callback method to be invoked when the window focus changes in the view tree.

|                                                                               Parameters                                                                                ||
|------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------|
| `hasFocus` | [Boolean](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html):Set to true if the window is gaining focus, false if it is losing focus. |