fix setInitialRoute (flutter/engine#6774)

* fix setInitialRoute

engine/src/flutter/.gitignore

@@ -20,3 +20,4 @@ tags
 Thumbs.db
 .idea
 pubspec.lock
+.vscode/

engine/src/flutter/shell/platform/darwin/ios/framework/Headers/FlutterEngine.h

@@ -78,7 +78,7 @@ FLUTTER_EXPORT
  *   tree-shaken by the Dart compiler.
  * @return YES if the call succeeds in creating and running a Flutter Engine instance; NO otherwise.
  */
-- (bool)runWithEntrypoint:(NSString*)entrypoint;
+- (BOOL)runWithEntrypoint:(NSString*)entrypoint;
 
 /**
  * Runs a Dart program on an Isolate using the specified entrypoint and Dart library,
@@ -95,7 +95,7 @@ FLUTTER_EXPORT
  *   this will default to the same library as the `main()` function in the Dart program.
  * @return YES if the call succeeds in creating and running a Flutter Engine instance; NO otherwise.
  */
-- (bool)runWithEntrypoint:(NSString*)entrypoint libraryURI:(NSString*)uri;
+- (BOOL)runWithEntrypoint:(NSString*)entrypoint libraryURI:(NSString*)uri;
 
 /**
  * Sets the `FlutterViewController` for this instance.  The FlutterEngine must be

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine.mm

@@ -264,10 +264,10 @@
       }));
 }
 
-- (bool)runWithEntrypoint:(NSString*)entrypoint libraryURI:(NSString*)libraryURI {
+- (BOOL)createShell:(NSString*)entrypoint libraryURI:(NSString*)libraryURI {
   if (_shell != nullptr) {
     FML_LOG(WARNING) << "This FlutterEngine was already invoked.";
-    return false;
+    return NO;
   }
 
   static size_t shellCount = 1;
@@ -351,13 +351,20 @@
                    << entrypoint.UTF8String;
   } else {
     [self maybeSetupPlatformViewChannels];
+  }
+
+  return _shell != nullptr;
+}
+
+- (BOOL)runWithEntrypoint:(NSString*)entrypoint libraryURI:(NSString*)libraryURI {
+  if ([self createShell:entrypoint libraryURI:libraryURI]) {
     [self launchEngine:entrypoint libraryURI:libraryURI];
   }
 
   return _shell != nullptr;
 }
 
-- (bool)runWithEntrypoint:(NSString*)entrypoint {
+- (BOOL)runWithEntrypoint:(NSString*)entrypoint {
   return [self runWithEntrypoint:entrypoint libraryURI:nil];
 }
 

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterEngine_Internal.h

@@ -42,6 +42,7 @@
 - (shell::FlutterPlatformViewsController*)platformViewsController;
 - (FlutterTextInputPlugin*)textInputPlugin;
 - (void)launchEngine:(NSString*)entrypoint libraryURI:(NSString*)libraryOrNil;
+- (BOOL)createShell:(NSString*)entrypoint libraryURI:(NSString*)libraryOrNil;
 
 @end
 

engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterViewController.mm

@@ -37,6 +37,7 @@
   blink::ViewportMetrics _viewportMetrics;
   BOOL _initialized;
   BOOL _viewOpaque;
+  BOOL _engineNeedsLaunch;
 }
 
 #pragma mark - Manage and override all designated initializers
@@ -49,6 +50,7 @@
   if (self) {
     _viewOpaque = YES;
     _engine.reset([engine retain]);
+    _engineNeedsLaunch = NO;
     _flutterView.reset([[FlutterView alloc] initWithDelegate:_engine opaque:self.isViewOpaque]);
     _weakFactory = std::make_unique<fml::WeakPtrFactory<FlutterViewController>>(self);
 
@@ -68,8 +70,8 @@
     _weakFactory = std::make_unique<fml::WeakPtrFactory<FlutterViewController>>(self);
     _engine.reset([[FlutterEngine alloc] initWithName:@"io.flutter" project:projectOrNil]);
     _flutterView.reset([[FlutterView alloc] initWithDelegate:_engine opaque:self.isViewOpaque]);
-    [_engine.get() runWithEntrypoint:nil];
-    [_engine.get() setViewController:self];
+    [_engine.get() createShell:nil libraryURI:nil];
+    _engineNeedsLaunch = YES;
 
     [self performCommonViewControllerInitialization];
   }
@@ -371,6 +373,12 @@
 - (void)viewWillAppear:(BOOL)animated {
   TRACE_EVENT0("flutter", "viewWillAppear");
 
+  if (_engineNeedsLaunch) {
+    [_engine.get() launchEngine:nil libraryURI:nil];
+    [_engine.get() setViewController:self];
+    _engineNeedsLaunch = NO;
+  }
+
   // Only recreate surface on subsequent appearances when viewport metrics are known.
   // First time surface creation is done on viewDidLayoutSubviews.
   if (_viewportMetrics.physical_width)