Make inForeground read only; add kdoc

Author: sunkup

app/src/main/kotlin/at/bitfire/davdroid/ui/AppTheme.kt

@@ -50,9 +50,9 @@ fun AppTheme(
 
     // Track if the app is in the foreground
     LifecycleResumeEffect(view) {
-        ForegroundTracker.inForeground.value = true
+        ForegroundTracker.onResume()
         onPauseOrDispose {
-            ForegroundTracker.inForeground.value = false
+            ForegroundTracker.onPaused()
         }
     }
 }

app/src/main/kotlin/at/bitfire/davdroid/ui/ForegroundTracker.kt

@@ -5,10 +5,31 @@
 package at.bitfire.davdroid.ui
 
 import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.asStateFlow
 
 /**
  * Used to track whether the app is in foreground (visible to user) or not.
  */
 object ForegroundTracker {
-    val inForeground: MutableStateFlow<Boolean> = MutableStateFlow(false)
+
+    private val _inForeground: MutableStateFlow<Boolean> = MutableStateFlow(false)
+
+    /**
+     * Whether the app is in foreground or not.
+     */
+    val inForeground = _inForeground.asStateFlow()
+
+    /**
+     * Called when the app is resumed (at [androidx.lifecycle.Lifecycle.Event.ON_RESUME])
+     */
+    fun onResume() {
+        _inForeground.value = true
+    }
+
+    /**
+     * Called when the app is paused (at [androidx.lifecycle.Lifecycle.Event.ON_PAUSE])
+     */
+    fun onPaused() {
+        _inForeground.value = false
+    }
 }