docs: update onlineManager documentation

Author: boschni

docs/src/pages/reference/onlineManager.md

@@ -18,20 +18,13 @@ Its available methods are:
 `setEventListener` can be used to set a custom event listener:
 
 ```js
+import NetInfo from '@react-native-community/netinfo'
 import { onlineManager } from 'react-query'
 
-onlineManager.setEventListener(handleOnline => {
-  // Listen to visibillitychange and online
-  if (typeof window !== 'undefined' && window.addEventListener) {
-    window.addEventListener('visibilitychange', handleOnline, false)
-    window.addEventListener('online', handleOnline, false)
-  }
-
-  return () => {
-    // Be sure to unsubscribe if a new handler is set
-    window.removeEventListener('visibilitychange', handleOnline)
-    window.removeEventListener('online', handleOnline)
-  }
+onlineManager.setEventListener(setOnline => {
+  return NetInfo.addEventListener(state => {
+    setOnline(state.isConnected)
+  })
 })
 ```
 

src/core/focusManager.ts

@@ -11,29 +11,31 @@ class FocusManager extends Subscribable {
     }
   }
 
-  setEventListener(setup: (onFocus: () => void) => () => void): void {
+  setEventListener(
+    setup: (onFocus: () => void) => (focused?: boolean) => void
+  ): void {
     if (this.removeEventListener) {
       this.removeEventListener()
     }
-    this.removeEventListener = setup(() => {
-      this.onFocus()
-    })
-  }
-
-  onFocus(): void {
-    this.listeners.forEach(listener => {
-      listener()
+    this.removeEventListener = setup((focused?: boolean) => {
+      this.setFocused(focused)
     })
   }
 
-  setFocused(focused: boolean | undefined): void {
+  setFocused(focused?: boolean): void {
     this.focused = focused
 
     if (focused) {
       this.onFocus()
     }
   }
 
+  onFocus(): void {
+    this.listeners.forEach(listener => {
+      listener()
+    })
+  }
+
   isFocused(): boolean {
     if (typeof this.focused === 'boolean') {
       return this.focused

src/core/onlineManager.ts

@@ -11,29 +11,31 @@ class OnlineManager extends Subscribable {
     }
   }
 
-  setEventListener(setup: (onOnline: () => void) => () => void): void {
+  setEventListener(
+    setup: (setOnline: () => void) => (online?: boolean) => void
+  ): void {
     if (this.removeEventListener) {
       this.removeEventListener()
     }
-    this.removeEventListener = setup(() => {
-      this.onOnline()
-    })
-  }
-
-  onOnline(): void {
-    this.listeners.forEach(listener => {
-      listener()
+    this.removeEventListener = setup((online?: boolean) => {
+      this.setOnline(online)
     })
   }
 
-  setOnline(online: boolean | undefined): void {
+  setOnline(online?: boolean): void {
     this.online = online
 
     if (online) {
       this.onOnline()
     }
   }
 
+  onOnline(): void {
+    this.listeners.forEach(listener => {
+      listener()
+    })
+  }
+
   isOnline(): boolean {
     if (typeof this.online === 'boolean') {
       return this.online