[android-components](../../index.md) / [mozilla.components.feature.readerview](../index.md) / [ReaderViewFeature](./index.md)

# ReaderViewFeature

`class ReaderViewFeature : `[`SelectionAwareSessionObserver`](../../mozilla.components.browser.session/-selection-aware-session-observer/index.md)`, `[`LifecycleAwareFeature`](../../mozilla.components.support.base.feature/-lifecycle-aware-feature/index.md)`, `[`BackHandler`](../../mozilla.components.support.base.feature/-back-handler/index.md) [(source)](https://github.com/mozilla-mobile/android-components/blob/master/components/feature/readerview/src/main/java/mozilla/components/feature/readerview/ReaderViewFeature.kt#L47)

Feature implementation that provides a reader view for the selected
session. This feature is implemented as a web extension and
needs to be installed prior to use (see [ReaderViewFeature.install](install.md)).

### Types

| Name | Summary |
|---|---|
| [ColorScheme](-color-scheme/index.md) | `enum class ColorScheme` |
| [Config](-config/index.md) | `inner class Config` |
| [FontType](-font-type/index.md) | `enum class FontType` |

### Constructors

| Name | Summary |
|---|---|
| [&lt;init&gt;](-init-.md) | `ReaderViewFeature(context: <ERROR CLASS>, engine: `[`Engine`](../../mozilla.components.concept.engine/-engine/index.md)`, sessionManager: `[`SessionManager`](../../mozilla.components.browser.session/-session-manager/index.md)`, controlsView: `[`ReaderViewControlsView`](../../mozilla.components.feature.readerview.view/-reader-view-controls-view/index.md)`, onReaderViewAvailableChange: `[`OnReaderViewAvailableChange`](../-on-reader-view-available-change.md)` = { })`<br>Feature implementation that provides a reader view for the selected session. This feature is implemented as a web extension and needs to be installed prior to use (see [ReaderViewFeature.install](install.md)). |

### Inherited Properties

| Name | Summary |
|---|---|
| [activeSession](../../mozilla.components.browser.session/-selection-aware-session-observer/active-session.md) | `open var activeSession: `[`Session`](../../mozilla.components.browser.session/-session/index.md)`?`<br>the currently observed session |

### Functions

| Name | Summary |
|---|---|
| [hideControls](hide-controls.md) | `fun hideControls(): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>Hides the reader view appearance controls. |
| [hideReaderView](hide-reader-view.md) | `fun hideReaderView(): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>Hides the reader view UI. |
| [onBackPressed](on-back-pressed.md) | `fun onBackPressed(): `[`Boolean`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html)<br>Called when this [BackHandler](../../mozilla.components.support.base.feature/-back-handler/index.md) gets the option to handle the user pressing the back key. |
| [onReaderableStateUpdated](on-readerable-state-updated.md) | `fun onReaderableStateUpdated(session: `[`Session`](../../mozilla.components.browser.session/-session/index.md)`, readerable: `[`Boolean`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-boolean/index.html)`): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html) |
| [onSessionAdded](on-session-added.md) | `fun onSessionAdded(session: `[`Session`](../../mozilla.components.browser.session/-session/index.md)`): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>The given session has been added. |
| [onSessionRemoved](on-session-removed.md) | `fun onSessionRemoved(session: `[`Session`](../../mozilla.components.browser.session/-session/index.md)`): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>The given session has been removed. |
| [onSessionSelected](on-session-selected.md) | `fun onSessionSelected(session: `[`Session`](../../mozilla.components.browser.session/-session/index.md)`): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>The selection has changed and the given session is now the selected session. |
| [onUrlChanged](on-url-changed.md) | `fun onUrlChanged(session: `[`Session`](../../mozilla.components.browser.session/-session/index.md)`, url: `[`String`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-string/index.html)`): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html) |
| [showControls](show-controls.md) | `fun showControls(): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>Shows the reader view appearance controls. |
| [showReaderView](show-reader-view.md) | `fun showReaderView(session: `[`Session`](../../mozilla.components.browser.session/-session/index.md)`? = activeSession): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>Shows the reader view UI. |
| [start](start.md) | `fun start(): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html) |
| [stop](stop.md) | `fun stop(): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>Stops the observer. |

### Inherited Functions

| Name | Summary |
|---|---|
| [observeFixed](../../mozilla.components.browser.session/-selection-aware-session-observer/observe-fixed.md) | `fun observeFixed(session: `[`Session`](../../mozilla.components.browser.session/-session/index.md)`): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>Starts observing changes to the specified session. |
| [observeIdOrSelected](../../mozilla.components.browser.session/-selection-aware-session-observer/observe-id-or-selected.md) | `fun observeIdOrSelected(sessionId: `[`String`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-string/index.html)`?): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>Starts observing changes to the session matching the [sessionId](../../mozilla.components.browser.session/-selection-aware-session-observer/observe-id-or-selected.md#mozilla.components.browser.session.SelectionAwareSessionObserver$observeIdOrSelected(kotlin.String)/sessionId). If the session does not exist, then observe the selected session. |
| [observeSelected](../../mozilla.components.browser.session/-selection-aware-session-observer/observe-selected.md) | `fun observeSelected(): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>Starts observing changes to the selected session (see [SessionManager.selectedSession](../../mozilla.components.browser.session/-session-manager/selected-session.md)). If a different session is selected the observer will automatically be switched over and only notified of changes to the newly selected session. |

### Companion Object Functions

| Name | Summary |
|---|---|
| [install](install.md) | `fun install(engine: `[`Engine`](../../mozilla.components.concept.engine/-engine/index.md)`): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html)<br>Installs the readerview web extension in the provided engine. |
| [registerMessageHandler](register-message-handler.md) | `fun registerMessageHandler(session: `[`EngineSession`](../../mozilla.components.concept.engine/-engine-session/index.md)`, messageHandler: `[`MessageHandler`](../../mozilla.components.concept.engine.webextension/-message-handler/index.md)`): `[`Unit`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-unit/index.html) |
