feat: changes the inital flutter route

fixes: /issues/276

Author: pchampio

application.go

@@ -13,6 +13,7 @@ import (
 	"github.com/go-flutter-desktop/go-flutter/embedder"
 	"github.com/go-flutter-desktop/go-flutter/internal/execpath"
 	"github.com/go-flutter-desktop/go-flutter/internal/opengl"
+	"github.com/go-flutter-desktop/go-flutter/plugin"
 )
 
 // Run executes a flutter application with the provided options.
@@ -270,6 +271,16 @@ func (a *Application) Run() error {
 		}
 	}
 
+	// Change the flutter initial route
+	initialRoute := os.Getenv("GOFLUTTER_ROUTE")
+	if initialRoute != "" {
+		defaultPlatformPlugin.flutterInitialized = func() {
+			plugin.
+				NewMethodChannel(messenger, "flutter/navigation", plugin.JSONMethodCodec{}).
+				InvokeMethod("pushRoute", initialRoute)
+		}
+	}
+
 	// Setup a new windowManager to handle windows pixel ratio's and pointer
 	// devices.
 	windowManager := newWindowManager(a.config.forcePixelRatio)

platform.go

@@ -19,11 +19,16 @@ type platformPlugin struct {
 	glfwTasker *tasker.Tasker
 	window     *glfw.Window
 	channel    *plugin.MethodChannel
+
+	// flutterInitialized gets called once flutter is running and ready
+	// to process upstream plugin calls. (It usually takes ~10 rendering frame).
+	flutterInitialized func()
 }
 
 // hardcoded because there is no swappable renderer interface.
 var defaultPlatformPlugin = &platformPlugin{
-	popBehavior: PopBehaviorNone,
+	popBehavior:        PopBehaviorNone,
+	flutterInitialized: func() {},
 }
 
 var _ Plugin = &platformPlugin{}     // compile-time type check
@@ -104,5 +109,8 @@ func (p *platformPlugin) handleWindowSetTitle(arguments interface{}) (reply inte
 	p.glfwTasker.Do(func() {
 		p.window.SetTitle(appSwitcherDescription.Label)
 	})
+
+	p.flutterInitialized()
+
 	return nil, nil
 }