I am developing an Android accessibility app in Kotlin. I want to provide full-screen magnification for users with visual impairments.

I use AccessibilityService.MagnificationController to set the magnification scale to 1.5. It works initially, but when I swipe to the Android home screen, the magnification resets to 1.0. The accessibility service remains enabled and connected.

I tried restoring the magnification once after detecting the reset. The API returns true, and the screen briefly becomes magnified again, but then returns to normal size.

Relevant Kotlin code:

val config = MagnificationConfig.Builder()
    .setMode(MagnificationConfig.MAGNIFICATION_MODE_FULLSCREEN)
    .setScale(1.5f)
    .setActivated(true)
    .build()

val result = magnificationController
    .setMagnificationConfig(config, true)

Log.d("Visionplus", "Result = $result")

The magnification change listener initially reports a scale of 1.5, but reports 1.0 after switching to the home screen.

Accessibility service XML configuration:

<accessibility-service
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:accessibilityEventTypes="typeAllMask"
    android:accessibilityFeedbackType="feedbackGeneric"
    android:canRetrieveWindowContent="true"
    android:description="@string/app_name"
    android:notificationTimeout="100"
    android:canControlMagnification="true" />

Environment:

• Android 15

• Pixel 7 emulator

• Kotlin and Android Studio

• Full-screen magnification mode

My question:

How can my AccessibilityService maintain full-screen magnification after switching to the Android home screen, if Android permits this? Is there a recommended way to use MagnificationController to handle magnification changes without repeatedly resetting the zoom?

Thank you for your help. I am new to Android development, so a simple explanation would be appreciated.

private val handler = Handler(Looper.getMainLooper())
private val reapplyZoom = Runnable {
    magnificationController.setMagnificationConfig(config, true)
}

override fun onAccessibilityEvent(event: AccessibilityEvent) {
    if (event.eventType == AccessibilityEvent.TYPE_WINDOW_STATE_CHANGED) {
        handler.removeCallbacks(reapplyZoom) // only the last event in a burst re-applies
        handler.postDelayed(reapplyZoom, 500)
    }
}