本文主要是針對 Flutter 在 iOS 上是如何運行起來的源碼進行串聯，總結大體的運行流程。c++
涉及到的關鍵類有如下幾個：git
Flutter 嵌入原生應用必須有個載體，從這個點入手，在 Flutter Engine 源碼中的 API 的入口點是 FlutterViewController，對其頭文件源碼作精簡，大體以下github
@interface FlutterViewController : UIViewController <FlutterTextureRegistry, FlutterPluginRegistry>
- (instancetype)initWithEngine:(FlutterEngine*)engine
nibName:(nullable NSString*)nibName
bundle:(nullable NSBundle*)nibBundle NS_DESIGNATED_INITIALIZER;
- (instancetype)initWithProject:(nullable FlutterDartProject*)project
nibName:(nullable NSString*)nibName
bundle:(nullable NSBundle*)nibBundle NS_DESIGNATED_INITIALIZER;
- (void)handleStatusBarTouches:(UIEvent*)event;
- (void)setFlutterViewDidRenderCallback:(void (^)(void))callback;
- (NSString*)lookupKeyForAsset:(NSString*)asset;
- (NSString*)lookupKeyForAsset:(NSString*)asset fromPackage:(NSString*)package;
- (void)setInitialRoute:(NSString*)route;
- (void)popRoute;
- (void)pushRoute:(NSString*)route;
- (id<FlutterPluginRegistry>)pluginRegistry;
@property(nonatomic, readonly, getter=isDisplayingFlutterUI) BOOL displayingFlutterUI;
@property(strong, nonatomic) UIView* splashScreenView;
- (BOOL)loadDefaultSplashScreenView;
@property(nonatomic, getter=isViewOpaque) BOOL viewOpaque;
@property(weak, nonatomic, readonly) FlutterEngine* engine;
@property(nonatomic, readonly) NSObject<FlutterBinaryMessenger>* binaryMessenger;
@end
FlutterViewController 有兩個構造函數，本質上是同樣的，第一個構造函數是谷歌爲了在存在多個 FlutterViewController 的場景下爲了讓使用者能複用 FlutterEngine 而開放的。web
- (instancetype)initWithEngine:(FlutterEngine*)engine
nibName:(nullable NSString*)nibName
bundle:(nullable NSBundle*)nibBundle {
NSAssert(engine != nil, @"Engine is required");
self = [super initWithNibName:nibName bundle:nibBundle];
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);
_ongoingTouches = [[NSMutableSet alloc] init];
[self performCommonViewControllerInitialization];
[engine setViewController:self];
}
return self;
}
- (instancetype)initWithProject:(nullable FlutterDartProject*)project
nibName:(nullable NSString*)nibName
bundle:(nullable NSBundle*)nibBundle {
self = [super initWithNibName:nibName bundle:nibBundle];
if (self) {
_viewOpaque = YES;
_weakFactory = std::make_unique<fml::WeakPtrFactory<FlutterViewController>>(self);
_engine.reset([[FlutterEngine alloc] initWithName:@"io.flutter"
project:project
allowHeadlessExecution:NO]);
_flutterView.reset([[FlutterView alloc] initWithDelegate:_engine opaque:self.isViewOpaque]);
[_engine.get() createShell:nil libraryURI:nil];
_engineNeedsLaunch = YES;
_ongoingTouches = [[NSMutableSet alloc] init];
[self loadDefaultSplashScreenView];
[self performCommonViewControllerInitialization];
}
return self;
}
在構造函數中主要作了這麼幾件事情：shell
初始化或者替換當前的 FlutterEnginejson
初始化 FlutterViewapi
初始化正在發生的手勢集合app
加載閃屏頁，傳入 FlutterEngine 的構造函數沒有這項，應該是考慮了多 FlutterViewController 的場景下很差頻繁加載閃屏頁less
設置 UIInterfaceOrientationMask 和 UIStatusBarStyleasync
添加一系列的通知，包括 Application 的生命週期，鍵盤事件，Accessibility的事件等
將 FlutterViewController 設置給 FlutterEngine
第二個構造函數中還多了這行代碼，第一個構造函數把這個調用延後了而已
[_engine.get() createShell:nil libraryURI:nil];
在 loadView 函數中，設置了 FlutterViewController 的 view，並判斷是否須要加載閃屏頁，能夠經過重寫 splashScreenView 的 get 方法返回 nil 的方式完全不加載閃屏頁
- (void)loadView {
self.view = _flutterView.get();
self.view.multipleTouchEnabled = YES;
self.view.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
[self installSplashScreenViewIfNecessary];
}
FlutterViewController 提供了三個接口容許咱們在原生端對 dart 的 Navigator 直接進行操做
- (void)setInitialRoute:(NSString*)route {
[[_engine.get() navigationChannel] invokeMethod:@"setInitialRoute" arguments:route];
}
- (void)popRoute {
[[_engine.get() navigationChannel] invokeMethod:@"popRoute" arguments:nil];
}
- (void)pushRoute:(NSString*)route {
[[_engine.get() navigationChannel] invokeMethod:@"pushRoute" arguments:route];
}
setInitialRoute 在 iOS 端經過 navigationChannel 來告訴 dart 具體的 initialRoute，這個過程略微特殊，並不會在 dart 端直接接收 channel 信息，
而是在引擎層面作了處理，web_ui 不在本文的解析範疇，這裏直接洗跟原生相關的點
setInitialRoute 設置流程以下：
DispatchPlatformMessage -> HandleNavigationPlatformMessage -> initial_route_
void Engine::DispatchPlatformMessage(fml::RefPtr<PlatformMessage> message) {
if (message->channel() == kLifecycleChannel) {
if (HandleLifecyclePlatformMessage(message.get()))
return;
} else if (message->channel() == kLocalizationChannel) {
if (HandleLocalizationPlatformMessage(message.get()))
return;
} else if (message->channel() == kSettingsChannel) {
HandleSettingsPlatformMessage(message.get());
return;
}
if (runtime_controller_->IsRootIsolateRunning() &&
runtime_controller_->DispatchPlatformMessage(std::move(message))) {
return;
}
// If there's no runtime_, we may still need to set the initial route.
if (message->channel() == kNavigationChannel) {
HandleNavigationPlatformMessage(std::move(message));
return;
}
FML_DLOG(WARNING) << "Dropping platform message on channel: "
<< message->channel();
}
bool Engine::HandleNavigationPlatformMessage(
fml::RefPtr<PlatformMessage> message) {
const auto& data = message->data();
rapidjson::Document document;
document.Parse(reinterpret_cast<const char*>(data.data()), data.size());
if (document.HasParseError() || !document.IsObject())
return false;
auto root = document.GetObject();
auto method = root.FindMember("method");
if (method->value != "setInitialRoute")
return false;
auto route = root.FindMember("args");
initial_route_ = std::move(route->value.GetString());
return true;
}
setInitialRoute 最終在 HandleNavigationPlatformMessage 函數中直接被賦值給 initial_route_。
setInitialRoute 讀取流程以下：
Window.defaultRouteName -> DefaultRouteName -> Engine::DefaultRouteName -> initial_route_
能夠看到，關鍵字 native，這是 dart 爲了方便綁定 C/C++ 導出方法而添加的關鍵字，對應的 key 是 Window_defaultRouteName
class Window {
String get defaultRouteName => _defaultRouteName();
String _defaultRouteName() native 'Window_defaultRouteName';
}
能夠找到在引擎層的 flutter 命名空間下，有下面這個函數，註冊了對應的導出函數，這裏對應的是 DefaultRouteName
void Window::RegisterNatives(tonic::DartLibraryNatives* natives) {
natives->Register({
{"Window_defaultRouteName", DefaultRouteName, 1, true},
{"Window_scheduleFrame", ScheduleFrame, 1, true},
{"Window_sendPlatformMessage", _SendPlatformMessage, 4, true},
{"Window_respondToPlatformMessage", _RespondToPlatformMessage, 3, true},
{"Window_render", Render, 2, true},
{"Window_updateSemantics", UpdateSemantics, 2, true},
{"Window_setIsolateDebugName", SetIsolateDebugName, 2, true},
{"Window_reportUnhandledException", ReportUnhandledException, 2, true},
{"Window_setNeedsReportTimings", SetNeedsReportTimings, 2, true},
});
}
void DefaultRouteName(Dart_NativeArguments args) {
std::string routeName =
UIDartState::Current()->window()->client()->DefaultRouteName();
Dart_SetReturnValue(args, tonic::StdStringToDart(routeName));
}
再往下就是到 engine.cc 文件下面的函數，讀取 initial_route_ 的值
std::string Engine::DefaultRouteName() {
if (!initial_route_.empty()) {
return initial_route_;
}
return "/";
}
至此，完成了在原生端設置 defaultRouteName，在 dart 端獲取該值的流程。
實現方式主要仍是經過引擎內置的 navigationChannel 通知 dart 端，對應的在 dart 端 SystemChannels 類中，存在對應的 channel
static const MethodChannel navigation = MethodChannel(
'flutter/navigation',
JSONMethodCodec(),
);
最終處理 pushRoute 和 popRoute 的邏輯在 WidgetsBinding 類中，主要是如下幾個函數
Future<dynamic> _handleNavigationInvocation(MethodCall methodCall) {
switch (methodCall.method) {
case 'popRoute':
return handlePopRoute();
case 'pushRoute':
return handlePushRoute(methodCall.arguments as String);
}
return Future<dynamic>.value();
}
Future<void> handlePushRoute(String route) async {
for (final WidgetsBindingObserver observer in List<WidgetsBindingObserver>.from(_observers)) {
if (await observer.didPushRoute(route))
return;
}
}
Future<void> handlePopRoute() async {
for (final WidgetsBindingObserver observer in List<WidgetsBindingObserver>.from(_observers)) {
if (await observer.didPopRoute())
return;
}
SystemNavigator.pop();
}
這段代碼表示只有調用的方法返回 true 時才中斷，每一個 handle 函數具體的處理邏輯是經過某個 WidgetsBindingObserver 來實現了，繼續跟進找到以下代碼
class _WidgetsAppState extends State<WidgetsApp> with WidgetsBindingObserver {
@override
Future<bool> didPopRoute() async {
assert(mounted);
final NavigatorState navigator = _navigator?.currentState;
if (navigator == null)
return false;
return await navigator.maybePop();
}
@override
Future<bool> didPushRoute(String route) async {
assert(mounted);
final NavigatorState navigator = _navigator?.currentState;
if (navigator == null)
return false;
navigator.pushNamed(route);
return true;
}
}
handlePopRoute 函數中，若是沒有任何一個 observer 返回 true，則最終調用 SystemNavigator.pop(); 來退出應用程序
class SystemNavigator {
static Future<void> pop({bool animated}) async {
await SystemChannels.platform.invokeMethod<void>('SystemNavigator.pop', animated);
}
}
FlutterView 並無太多功能，主要是兩點：
FlutterViewEngineDelegateflutter::IOSSurface@protocol FlutterViewEngineDelegate <NSObject>
- (flutter::Rasterizer::Screenshot)takeScreenshot:(flutter::Rasterizer::ScreenshotType)type
asBase64Encoded:(BOOL)base64Encode;
- (flutter::FlutterPlatformViewsController*)platformViewsController;
@end
@interface FlutterView : UIView
- (instancetype)initWithDelegate:(id<FlutterViewEngineDelegate>)delegate
opaque:(BOOL)opaque NS_DESIGNATED_INITIALIZER;
- (std::unique_ptr<flutter::IOSSurface>)createSurface:
(std::shared_ptr<flutter::IOSGLContext>)context;
@end
takeScreenshot:asBase64Encoded: 應該是 FlutterView 渲染的數據源，具體參考 drawLayer:inContext: 的源碼
@implementation FlutterView
- (void)drawLayer:(CALayer*)layer inContext:(CGContextRef)context {
if (layer != self.layer || context == nullptr) {
return;
}
auto screenshot = [_delegate takeScreenshot:flutter::Rasterizer::ScreenshotType::UncompressedImage
asBase64Encoded:NO];
if (!screenshot.data || screenshot.data->isEmpty() || screenshot.frame_size.isEmpty()) {
return;
}
NSData* data = [NSData dataWithBytes:const_cast<void*>(screenshot.data->data())
length:screenshot.data->size()];
fml::CFRef<CGDataProviderRef> image_data_provider(
CGDataProviderCreateWithCFData(reinterpret_cast<CFDataRef>(data)));
fml::CFRef<CGColorSpaceRef> colorspace(CGColorSpaceCreateDeviceRGB());
fml::CFRef<CGImageRef> image(CGImageCreate(
screenshot.frame_size.width(), // size_t width
screenshot.frame_size.height(), // size_t height
8, // size_t bitsPerComponent
32, // size_t bitsPerPixel,
4 * screenshot.frame_size.width(), // size_t bytesPerRow
colorspace, // CGColorSpaceRef space
static_cast<CGBitmapInfo>(kCGImageAlphaPremultipliedLast |
kCGBitmapByteOrder32Big), // CGBitmapInfo bitmapInfo
image_data_provider, // CGDataProviderRef provider
nullptr, // const CGFloat* decode
false, // bool shouldInterpolate
kCGRenderingIntentDefault // CGColorRenderingIntent intent
));
const CGRect frame_rect =
CGRectMake(0.0, 0.0, screenshot.frame_size.width(), screenshot.frame_size.height());
CGContextSaveGState(context);
CGContextTranslateCTM(context, 0.0, CGBitmapContextGetHeight(context));
CGContextScaleCTM(context, 1.0, -1.0);
CGContextDrawImage(context, frame_rect, image);
CGContextRestoreGState(context);
}
@end
後面咱們會看到 FlutterViewEngineDelegate 其實是被 FlutterEngine 實現了。
這裏不對 IOSSurface 作過多解析，其是創建在三種 layer 之上的，能夠在編譯期選擇使用何種渲染方式
+ (Class)layerClass {
#if TARGET_IPHONE_SIMULATOR
return [CALayer class];
#else // TARGET_IPHONE_SIMULATOR
#if FLUTTER_SHELL_ENABLE_METAL
return [CAMetalLayer class];
#else // FLUTTER_SHELL_ENABLE_METAL
return [CAEAGLLayer class];
#endif // FLUTTER_SHELL_ENABLE_METAL
#endif // TARGET_IPHONE_SIMULATOR
}
在 createSurface 函數中主要是分別建立三種對應的 IOSSurface
CALayer -> IOSSurfaceSoftware
CAEAGLLayer -> IOSSurfaceGL
CAMetalLayer -> IOSSurfaceMetal
再往下的渲染實際上就要交給 FlutterEngine 自身了。
FlutterEngine 對外暴露的接口不算多，主要就這麼幾點
initWithName:project:allowHeadlessExecution，allowHeadlessExecution容許初始化引擎時不強依賴FlutterViewController`runWithEntrypoint:libraryURI: 可傳入自定義的 entrypointdestroyContextensureSemanticsEnabled，關於語義樹文檔比較少，大概是殘疾人模式下須要用到的東西FlutterViewController 的 get/set咱們主要關心引擎的構造、啓動、釋放和 FlutterViewController 就差很少了，FlutterTextureRegistry, FlutterPluginRegistry 不在本文關注範圍內
@interface FlutterEngine : NSObject <FlutterTextureRegistry, FlutterPluginRegistry>
- (instancetype)initWithName:(NSString*)labelPrefix
project:(nullable FlutterDartProject*)project
allowHeadlessExecution:(BOOL)allowHeadlessExecution NS_DESIGNATED_INITIALIZER;
- (BOOL)runWithEntrypoint:(nullable NSString*)entrypoint libraryURI:(nullable NSString*)uri;
- (void)destroyContext;
- (void)ensureSemanticsEnabled;
@property(nonatomic, weak) FlutterViewController* viewController;
@property(nonatomic, readonly, nullable) FlutterMethodChannel* localizationChannel;
@property(nonatomic, readonly) FlutterMethodChannel* navigationChannel;
@property(nonatomic, readonly) FlutterMethodChannel* platformChannel;
@property(nonatomic, readonly) FlutterMethodChannel* textInputChannel;
@property(nonatomic, readonly) FlutterBasicMessageChannel* lifecycleChannel;
@property(nonatomic, readonly) FlutterBasicMessageChannel* systemChannel;
@property(nonatomic, readonly) FlutterBasicMessageChannel* settingsChannel;
@property(nonatomic, readonly) NSObject<FlutterBinaryMessenger>* binaryMessenger;
@property(nonatomic, readonly, copy, nullable) NSString* isolateId;
@end
FlutterEngine在構造時，要關注的有幾下兩點：
FlutterDartProject 初始化FlutterPlatformViewsController 的初始化- (instancetype)initWithName:(NSString*)labelPrefix
project:(FlutterDartProject*)project
allowHeadlessExecution:(BOOL)allowHeadlessExecution {
self = [super init];
NSAssert(self, @"Super init cannot be nil");
NSAssert(labelPrefix, @"labelPrefix is required");
_allowHeadlessExecution = allowHeadlessExecution;
_labelPrefix = [labelPrefix copy];
_weakFactory = std::make_unique<fml::WeakPtrFactory<FlutterEngine>>(self);
if (project == nil)
_dartProject.reset([[FlutterDartProject alloc] init]);
else
_dartProject.reset([project retain]);
_pluginPublications = [NSMutableDictionary new];
_platformViewsController.reset(new flutter::FlutterPlatformViewsController());
_binaryMessenger = [[FlutterBinaryMessengerRelay alloc] initWithParent:self];
NSNotificationCenter* center = [NSNotificationCenter defaultCenter];
[center addObserver:self
selector:@selector(onMemoryWarning:)
name:UIApplicationDidReceiveMemoryWarningNotification
object:nil];
return self;
}
FlutterEngine 層面，須要關注如下一些類：
FlutterEngine 的啓動，主要是兩個事情
- (BOOL)runWithEntrypoint:(NSString*)entrypoint libraryURI:(NSString*)libraryURI {
if ([self createShell:entrypoint libraryURI:libraryURI]) {
[self launchEngine:entrypoint libraryURI:libraryURI];
}
return _shell != nullptr;
}
createShell 的源碼比較多，作了下精簡，主要是如下幾點：
MessageLoopThreadHoston_create_platform_view 回調on_create_rasterizer 回調flutter::TaskRunners，若是開啓 embedded_views_preview 則 使用當前線程的 TaskRunner 做爲 gpu 線程的 TaskRunnershell，最終是啓動 IsolateFlutterPlatformViewsControllerFlutterObservatoryPublisherPlatformView channels- (BOOL)createShell:(NSString*)entrypoint libraryURI:(NSString*)libraryURI {
// ……
fml::MessageLoop::EnsureInitializedForCurrentThread();
_threadHost = {threadLabel.UTF8String, flutter::ThreadHost::Type::UI |
flutter::ThreadHost::Type::GPU |
flutter::ThreadHost::Type::IO};
flutter::Shell::CreateCallback<flutter::PlatformView> on_create_platform_view =
[](flutter::Shell& shell) {
return std::make_unique<flutter::PlatformViewIOS>(shell, shell.GetTaskRunners());
};
flutter::Shell::CreateCallback<flutter::Rasterizer> on_create_rasterizer =
[](flutter::Shell& shell) {
return std::make_unique<flutter::Rasterizer>(shell, shell.GetTaskRunners());
};
if (flutter::IsIosEmbeddedViewsPreviewEnabled()) {
flutter::TaskRunners task_runners(threadLabel.UTF8String, // label
fml::MessageLoop::GetCurrent().GetTaskRunner(), // platform
fml::MessageLoop::GetCurrent().GetTaskRunner(), // gpu
_threadHost.ui_thread->GetTaskRunner(), // ui
_threadHost.io_thread->GetTaskRunner() // io
);
// Create the shell. This is a blocking operation.
_shell = flutter::Shell::Create(std::move(task_runners), // task runners
std::move(settings), // settings
on_create_platform_view, // platform view creation
on_create_rasterizer // rasterzier creation
);
} else {
flutter::TaskRunners task_runners(threadLabel.UTF8String, // label
fml::MessageLoop::GetCurrent().GetTaskRunner(), // platform
_threadHost.gpu_thread->GetTaskRunner(), // gpu
_threadHost.ui_thread->GetTaskRunner(), // ui
_threadHost.io_thread->GetTaskRunner() // io
);
// Create the shell. This is a blocking operation.
_shell = flutter::Shell::Create(std::move(task_runners), // task runners
std::move(settings), // settings
on_create_platform_view, // platform view creation
on_create_rasterizer // rasterzier creation
);
}
if (_shell != nullptr) {
[self setupChannels];
if (!_platformViewsController) {
_platformViewsController.reset(new flutter::FlutterPlatformViewsController());
}
_publisher.reset([[FlutterObservatoryPublisher alloc] init]);
[self maybeSetupPlatformViewChannels];
}
return _shell != nullptr;
}
這裏能夠看到會啓動四個 TaskRunner，分別爲 platform,gpu, ui,io，但實際上並不必定對應四個線程。
launchEngine 實際上仍是在 shell 上進行的操做
- (void)launchEngine:(NSString*)entrypoint libraryURI:(NSString*)libraryOrNil {
// Launch the Dart application with the inferred run configuration.
self.shell.RunEngine([_dartProject.get() runConfigurationForEntrypoint:entrypoint
libraryOrNil:libraryOrNil]);
}
void Shell::RunEngine(RunConfiguration run_configuration) {
RunEngine(std::move(run_configuration), nullptr);
}
void Shell::RunEngine(RunConfiguration run_configuration,
std::function<void(Engine::RunStatus)> result_callback) {
auto result = [platform_runner = task_runners_.GetPlatformTaskRunner(),
result_callback](Engine::RunStatus run_result) {
if (!result_callback) {
return;
}
platform_runner->PostTask(
[result_callback, run_result]() { result_callback(run_result); });
};
FML_DCHECK(is_setup_);
FML_DCHECK(task_runners_.GetPlatformTaskRunner()->RunsTasksOnCurrentThread());
if (!weak_engine_) {
result(Engine::RunStatus::Failure);
}
fml::TaskRunner::RunNowOrPostTask(
task_runners_.GetUITaskRunner(),
fml::MakeCopyable(
[run_configuration = std::move(run_configuration),
weak_engine = weak_engine_, result]() mutable {
if (!weak_engine) {
FML_LOG(ERROR)
<< "Could not launch engine with configuration - no engine.";
result(Engine::RunStatus::Failure);
return;
}
auto run_result = weak_engine->Run(std::move(run_configuration));
if (run_result == flutter::Engine::RunStatus::Failure) {
FML_LOG(ERROR) << "Could not launch engine with configuration.";
}
result(run_result);
}));
}
再跟下去，最終會到[shell > common > engine.cc] 裏面的 run 函數，最核心的是這行代碼 PrepareAndLaunchIsolate，最終整個流程跑下來就是爲了啓動 Isolate
Engine::RunStatus Engine::Run(RunConfiguration configuration) {
if (!configuration.IsValid()) {
FML_LOG(ERROR) << "Engine run configuration was invalid.";
return RunStatus::Failure;
}
auto isolate_launch_status =
PrepareAndLaunchIsolate(std::move(configuration));
if (isolate_launch_status == Engine::RunStatus::Failure) {
FML_LOG(ERROR) << "Engine not prepare and launch isolate.";
return isolate_launch_status;
} else if (isolate_launch_status ==
Engine::RunStatus::FailureAlreadyRunning) {
return isolate_launch_status;
}
std::shared_ptr<DartIsolate> isolate =
runtime_controller_->GetRootIsolate().lock();
bool isolate_running =
isolate && isolate->GetPhase() == DartIsolate::Phase::Running;
if (isolate_running) {
tonic::DartState::Scope scope(isolate.get());
if (settings_.root_isolate_create_callback) {
settings_.root_isolate_create_callback();
}
if (settings_.root_isolate_shutdown_callback) {
isolate->AddIsolateShutdownCallback(
settings_.root_isolate_shutdown_callback);
}
std::string service_id = isolate->GetServiceId();
fml::RefPtr<PlatformMessage> service_id_message =
fml::MakeRefCounted<flutter::PlatformMessage>(
kIsolateChannel,
std::vector<uint8_t>(service_id.begin(), service_id.end()),
nullptr);
HandlePlatformMessage(service_id_message);
}
return isolate_running ? Engine::RunStatus::Success
: Engine::RunStatus::Failure;
}
對 PrepareAndLaunchIsolate 函數作下精簡，剩下兩個點
Engine::RunStatus Engine::PrepareAndLaunchIsolate(RunConfiguration configuration) {
// ……
if (!isolate_configuration->PrepareIsolate(*isolate)) {
return RunStatus::Failure;
}
if (!isolate->RunFromLibrary(configuration.GetEntrypointLibrary(),
configuration.GetEntrypoint(),
settings_.dart_entrypoint_args)) {
return RunStatus::Failure;
}
return RunStatus::Success;
}
主要看看 RunFromLibrary 作了什麼
InvokeMainEntrypointbool DartIsolate::RunFromLibrary(const std::string& library_name,
const std::string& entrypoint_name,
const std::vector<std::string>& args,
fml::closure on_run) {
tonic::DartState::Scope scope(this);
auto user_entrypoint_function =
Dart_GetField(Dart_LookupLibrary(tonic::ToDart(library_name.c_str())),
tonic::ToDart(entrypoint_name.c_str()));
auto entrypoint_args = tonic::ToDart(args);
if (!InvokeMainEntrypoint(user_entrypoint_function, entrypoint_args)) {
return false;
}
phase_ = Phase::Running;
if (on_run) {
on_run();
}
return true;
}
再看看 InvokeMainEntrypoint 作了什麼，源碼作了精簡，主要就這兩步，咱們能夠在 dart 端找到對應的函數
_getStartMainIsolateFunction_runMainZonedstatic bool InvokeMainEntrypoint(Dart_Handle user_entrypoint_function,
Dart_Handle args) {
Dart_Handle start_main_isolate_function =
tonic::DartInvokeField(Dart_LookupLibrary(tonic::ToDart("dart:isolate")),
"_getStartMainIsolateFunction", {});
if (tonic::LogIfError(tonic::DartInvokeField(
Dart_LookupLibrary(tonic::ToDart("dart:ui")), "_runMainZoned",
{start_main_isolate_function, user_entrypoint_function, args}))) {
FML_LOG(ERROR) << "Could not invoke the main entrypoint.";
return false;
}
return true;
}
再往下就是 tonic 庫，這是 fuchsia 下的庫，谷歌並未開源到 github 上，但能夠在這裏看到 googlesource，後面可能會在其它文章中對 tonic 庫進行梳理。
Flutter 運行於 iOS 之上，從源碼層面看，有如下幾點收穫：
drawLayer 時會調用 takeScreenshot 來獲取 Flutter 界面的光柵圖TaskRunner，Platform TaskRunner 不必定是獨立的線程native 關鍵字調用 C/C++ 的函數，獲取基本類型的數據返回值，性能比 channel 要好FlutterViewController 將全部的手勢交互相關的都轉發給 FlutterEngine對整個 Flutter 運行的流程能夠大體總結以下，主要是側重在引擎側，dart 那邊的流程不展開，僅供參考：
FlutterEngine，傳入 DartLibrary 和 EntrypointFlutterViewController，FlutterViewFlutterEngine 的 viewController