diff --git a/examples/platform_channel/macos/Runner/MainFlutterWindow.swift b/examples/platform_channel/macos/Runner/MainFlutterWindow.swift
index 16df5f6335..239c019ddf 100644
--- a/examples/platform_channel/macos/Runner/MainFlutterWindow.swift
+++ b/examples/platform_channel/macos/Runner/MainFlutterWindow.swift
@@ -5,15 +5,16 @@
 import Cocoa
 import FlutterMacOS
 
-class MainFlutterWindow: NSWindow, FlutterStreamHandler, PowerSourceStateChangeDelegate {
+class MainFlutterWindow: NSWindow {
   private let powerSource = PowerSource()
-  private let stateChangeSource = PowerSourceStateChangeHandler()
+  private let stateChangeHandler = PowerSourceStateChangeHandler()
   private var eventSink: FlutterEventSink?
 
   override func awakeFromNib() {
     let flutterViewController = FlutterViewController()
     let windowFrame = self.frame
     self.contentViewController = flutterViewController
+    self.displayIfNeeded()
     self.setFrame(windowFrame, display: true)
 
     // Register battery method channel.
@@ -21,18 +22,18 @@ class MainFlutterWindow: NSWindow, FlutterStreamHandler, PowerSourceStateChangeD
     let batteryChannel = FlutterMethodChannel(
       name: "samples.flutter.io/battery",
       binaryMessenger: registrar.messenger)
-    batteryChannel.setMethodCallHandler({ [weak self] (call, result) in
+    batteryChannel.setMethodCallHandler { [powerSource = self.powerSource] (call, result) in
       switch call.method {
       case "getBatteryLevel":
-        if self?.powerSource.hasBattery() == false {
-          result(FlutterError(
-            code: "NO_BATTERY",
-            message: "Device does not have a battery",
-            details: nil))
+        guard powerSource.hasBattery() else {
+          result(
+            FlutterError(
+              code: "NO_BATTERY",
+              message: "Device does not have a battery",
+              details: nil))
           return
         }
-        let level = self?.powerSource.getCurrentCapacity()
-        if level == -1 {
+        guard let level = powerSource.getCurrentCapacity() else {
           result(
             FlutterError(
               code: "UNAVAILABLE",
@@ -44,7 +45,7 @@ class MainFlutterWindow: NSWindow, FlutterStreamHandler, PowerSourceStateChangeD
       default:
         result(FlutterMethodNotImplemented)
       }
-    })
+    }
 
     // Register charging event channel.
     let chargingChannel = FlutterEventChannel(
@@ -57,25 +58,7 @@ class MainFlutterWindow: NSWindow, FlutterStreamHandler, PowerSourceStateChangeD
     super.awakeFromNib()
   }
 
-  func onListen(withArguments arguments: Any?, eventSink events: @escaping FlutterEventSink)
-    -> FlutterError?
-  {
-    self.eventSink = events
-    self.emitPowerStatusEvent()
-    self.stateChangeSource.delegate = self
-    return nil
-  }
-
-  func onCancel(withArguments arguments: Any?) -> FlutterError? {
-    self.stateChangeSource.delegate = nil
-    self.eventSink = nil
-    return nil
-  }
-
-  func onPowerSourceStateChanged() {
-    self.emitPowerStatusEvent()
-  }
-
+  /// Emit a power status event to the registered event sink.
   func emitPowerStatusEvent() {
     if let sink = self.eventSink {
       switch self.powerSource.getPowerState() {
@@ -88,5 +71,27 @@ class MainFlutterWindow: NSWindow, FlutterStreamHandler, PowerSourceStateChangeD
       }
     }
   }
-
+}
+
+extension MainFlutterWindow: FlutterStreamHandler {
+  func onListen(withArguments arguments: Any?, eventSink events: @escaping FlutterEventSink)
+    -> FlutterError?
+  {
+    self.eventSink = events
+    self.emitPowerStatusEvent()
+    self.stateChangeHandler.delegate = self
+    return nil
+  }
+
+  func onCancel(withArguments arguments: Any?) -> FlutterError? {
+    self.stateChangeHandler.delegate = nil
+    self.eventSink = nil
+    return nil
+  }
+}
+
+extension MainFlutterWindow: PowerSourceStateChangeDelegate {
+  func didChangePowerSourceState() {
+    self.emitPowerStatusEvent()
+  }
 }
diff --git a/examples/platform_channel/macos/Runner/PowerSource.swift b/examples/platform_channel/macos/Runner/PowerSource.swift
index d1b14d830c..c465b2a611 100644
--- a/examples/platform_channel/macos/Runner/PowerSource.swift
+++ b/examples/platform_channel/macos/Runner/PowerSource.swift
@@ -12,9 +12,13 @@ enum PowerState {
 }
 
 /// A convenience wrapper for an IOKit power source.
-class PowerSource {
+final class PowerSource {
   let info = IOPSCopyPowerSourcesInfo().takeRetainedValue()
-  lazy var sources = IOPSCopyPowerSourcesList(info).takeRetainedValue() as Array
+  let sources: Array<CFTypeRef>
+
+  init() {
+    sources = IOPSCopyPowerSourcesList(info).takeRetainedValue() as Array
+  }
 
   func hasBattery() -> Bool {
     return !sources.isEmpty
@@ -22,7 +26,7 @@ class PowerSource {
 
   /// Returns the current power source capacity. Apple-defined power sources will return this value
   /// as a percentage.
-  func getCurrentCapacity() -> Int {
+  func getCurrentCapacity() -> Int? {
     if let source = sources.first {
       let description =
         IOPSGetPowerSourceDescription(info, source).takeUnretainedValue() as! [String: AnyObject]
@@ -30,7 +34,7 @@ class PowerSource {
         return level
       }
     }
-    return -1
+    return nil
   }
 
   /// Returns whether the device is drawing battery power or connected to an external power source.
@@ -54,11 +58,11 @@ class PowerSource {
 }
 
 protocol PowerSourceStateChangeDelegate: AnyObject {
-  func onPowerSourceStateChanged()
+  func didChangePowerSourceState()
 }
 
 /// A listener for system power source state change events. Notifies the delegate on each event.
-class PowerSourceStateChangeHandler {
+final class PowerSourceStateChangeHandler {
   private var runLoopSource: CFRunLoopSource?
   weak var delegate: PowerSourceStateChangeDelegate?
 
@@ -66,10 +70,10 @@ class PowerSourceStateChangeHandler {
     let context = UnsafeMutableRawPointer(Unmanaged.passUnretained(self).toOpaque())
     self.runLoopSource = IOPSNotificationCreateRunLoopSource(
       { (context: UnsafeMutableRawPointer?) in
-        let weakSelf = Unmanaged<PowerSourceStateChangeHandler>.fromOpaque(
+        let unownedSelf = Unmanaged<PowerSourceStateChangeHandler>.fromOpaque(
           UnsafeRawPointer(context!)
         ).takeUnretainedValue()
-        weakSelf.delegate?.onPowerSourceStateChanged()
+        unownedSelf.delegate?.didChangePowerSourceState()
       }, context
     ).takeRetainedValue()
     CFRunLoopAddSource(CFRunLoopGetCurrent(), self.runLoopSource, .defaultMode)