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Jetpack-Compose-Playground/docs/general/compositionlocal.md

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+<!---
+This is the API of version 1.2.0
+-->
+# CompositionLocal
+
+
+CompositionLocal is useful when you want to create a dependency in a higher node of the layout tree and use it on lower node without having to
+pass it down the tree through every child Composable.
+
+## How to create an CompositionLocal?
+```kotlin
+data class User(val name: String, val age: Int)
+val LocalActiveUser = compositionLocalOf<User> { error("No user found!") }
+```
+Let's say you want to create an CompositionLocal with an User. You can use **compositionLocalOf**. Inside the function you can return an initial user object
+ or you can throw an exception when the user is missing.
+
+## How to provide a value for an CompositionLocal?
+
+```kotlin
+@Composable
+private fun MyUserScreen() {
+    val user = User("Jens", 31)
+    CompositionLocalProvider(LocalActiveUser provides user) {
+        UserInfo()
+    }
+}
+```
+Somewhere above in your hierarchy you have to use CompositionLocalProvider to provide a value for your CompositionLocal.
+The syntax is: "**CompositionLocal`<T>`** provides **T**".
+All child @Composable of CompositionLocalProvider will implicitly be able to get the value of the CompositionLocals.
+
+## How to use a value of an CompositionLocal?
+
+```kotlin
+@Preview
+@Composable
+fun UserInfo() {
+    Column {
+        Text("Name: " + LocalActiveUser.current.name)
+        Text("Age: " + LocalActiveUser.current.age)
+    }
+}
+```
+
+Now you can use your CompositionLocal in your @Composable. Every CompositionLocal has a **current** property that contains the current value.
+
+## Predefined CompositionLocals
+The Compose libraries already contain some useful CompositionLocals. You can directly use them without needing add a Providers.
+
+### LocalContext
+Provides a [Context] that can be used by Android applications.
+
+### LocalConfiguration
+The [Configuration] is useful for determining how to organize the UI.
+
+#### Device orientation
+One of the things you can get from the LocalConfiguration is the orientation of your device. This can be used to give the user a different ui when the device is rotated.
+
+```kotlin
+val configuration = LocalConfiguration.current
+when (configuration.orientation) {
+    Configuration.ORIENTATION_LANDSCAPE -> {
+        Text("Landscape")
+    }
+    else -> {
+        Text("Portrait")
+    }
+}
+```
+
+### LocalLifecycleOwner
+The CompositionLocal containing the current [LifecycleOwner].
+
+### LocalView
+ The CompositionLocal containing the current Compose [View].
+
+### LocalViewModelStoreOwner
+The CompositionLocal containing the current [ViewModelStoreOwner].
+
+
+## See also:
+* [Official Docs](https://developer.android.com/reference/kotlin/androidx/compose/runtime/CompositionLocal)
+* [Full Example Code]({{ site.samplefolder }}/general/CompositionLocalExample.kt)
+