[platform_channels] adds ios implementation for MethodChannel demo (#563)

platform_channels/ios/Runner/AppDelegate.swift

@@ -3,11 +3,30 @@ import Flutter
 
 @UIApplicationMain
 @objc class AppDelegate: FlutterAppDelegate {
-  override func application(
-    _ application: UIApplication,
-    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
-  ) -> Bool {
-    GeneratedPluginRegistrant.register(with: self)
-    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
-  }
+    override func application(
+        _ application: UIApplication,
+        didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
+    ) -> Bool {
+        let flutterViewController = window.rootViewController as! FlutterViewController
+        FlutterMethodChannel(name: "methodChannelDemo", binaryMessenger: flutterViewController.binaryMessenger).setMethodCallHandler({
+            (call: FlutterMethodCall, result: FlutterResult) -> Void in
+            
+            guard let count = (call.arguments as? NSDictionary)?["count"] as? Int else {
+                result(FlutterError(code: "INVALID_ARGUMENT", message: "Value of count cannot be null", details: nil))
+                return
+            }
+            
+            switch call.method {
+            case "increment":
+                result(count + 1)
+            case "decrement":
+                result(count - 1)
+            default:
+                result(FlutterMethodNotImplemented)
+            }
+        })
+        
+        GeneratedPluginRegistrant.register(with: self)
+        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
+    }
 }