在 iOS 应用中添加 Flutter 页面

本指南描述了怎样在既有 iOS 应用中添加单个 Flutter 页面。

启动 FlutterEngine 和 FlutterViewController

为了在既有 iOS 应用中展示 Flutter 页面,请启动 FlutterEngineFlutterViewController

FlutterEngine 的寿命可能与 FlutterViewController 相同,也可能超过 FlutterViewController

加载顺序和性能 里有更多关于预热 engine 的延迟和内存取舍的分析。

创建一个 FlutterEngine

创建 FlutterEngine 的合适位置取决于您的应用。作为示例,我们将在应用启动的 app delegate 中创建一个 FlutterEngine,并作为属性暴露给外界。

In AppDelegate.swift:

import UIKit
import Flutter
// Used to connect plugins (only if you have plugins with iOS platform code).
import FlutterPluginRegistrant

@UIApplicationMain
class AppDelegate: FlutterAppDelegate { // More on the FlutterAppDelegate.
  lazy var flutterEngine = FlutterEngine(name: "my flutter engine")

  override func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    // Runs the default Dart entrypoint with a default Flutter route.
    flutterEngine.run();
    // Used to connect plugins (only if you have plugins with iOS platform code).
    GeneratedPluginRegistrant.register(with: self.flutterEngine);
    return super.application(application, didFinishLaunchingWithOptions: launchOptions);
  }
}

AppDelegate.h:

@import UIKit;
@import Flutter;

@interface AppDelegate : FlutterAppDelegate // More on the FlutterAppDelegate below.
@property (nonatomic,strong) FlutterEngine *flutterEngine;
@end

AppDelegate.m:

// Used to connect plugins (only if you have plugins with iOS platform code).
#import <FlutterPluginRegistrant/GeneratedPluginRegistrant.h>

#import "AppDelegate.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application
    didFinishLaunchingWithOptions:(NSDictionary<UIApplicationLaunchOptionsKey, id> *)launchOptions {
  self.flutterEngine = [[FlutterEngine alloc] initWithName:@"my flutter engine"];
  // Runs the default Dart entrypoint with a default Flutter route.
  [self.flutterEngine run];
  // Used to connect plugins (only if you have plugins with iOS platform code).
  [GeneratedPluginRegistrant registerWithRegistry:self.flutterEngine];
  return [super application:application didFinishLaunchingWithOptions:launchOptions];
}

@end

使用 FlutterEngine 展示 FlutterViewController

下面的例子展示了一个普通的 ViewController,包含一个能跳转到 FlutterViewControllerUIButton,这个 FlutterViewController 使用在 AppDelegate 中创建的 Flutter 引擎 (FlutterEngine)。

import UIKit
import Flutter

class ViewController: UIViewController {
  override func viewDidLoad() {
    super.viewDidLoad()

    // Make a button to call the showFlutter function when pressed.
    let button = UIButton(type:UIButton.ButtonType.custom)
    button.addTarget(self, action: #selector(showFlutter), for: .touchUpInside)
    button.setTitle("Show Flutter!", for: UIControl.State.normal)
    button.frame = CGRect(x: 80.0, y: 210.0, width: 160.0, height: 40.0)
    button.backgroundColor = UIColor.blue
    self.view.addSubview(button)
  }

  @objc func showFlutter() {
    let flutterEngine = (UIApplication.shared.delegate as! AppDelegate).flutterEngine
    let flutterViewController =
        FlutterViewController(engine: flutterEngine, nibName: nil, bundle: nil)
    present(flutterViewController, animated: true, completion: nil)
  }
}
@import Flutter;
#import "AppDelegate.h"
#import "ViewController.h"

@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];

    // Make a button to call the showFlutter function when pressed.
    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
    [button addTarget:self
               action:@selector(showFlutter)
     forControlEvents:UIControlEventTouchUpInside];
    [button setTitle:@"Show Flutter!" forState:UIControlStateNormal];
    button.backgroundColor = UIColor.blueColor;
    button.frame = CGRectMake(80.0, 210.0, 160.0, 40.0);
    [self.view addSubview:button];
}

- (void)showFlutter {
    FlutterEngine *flutterEngine =
        ((AppDelegate *)UIApplication.sharedApplication.delegate).flutterEngine;
    FlutterViewController *flutterViewController =
        [[FlutterViewController alloc] initWithEngine:flutterEngine nibName:nil bundle:nil];
    [self presentViewController:flutterViewController animated:YES completion:nil];
}
@end

现在,你的 iOS 应用中集成了一个 Flutter 页面。

或者 —— 使用隐式 FlutterEngine 创建 FlutterViewController

上一个示例还有另一个选择,你可以让 FlutterViewController 隐式创建它自己的 FlutterEngine,而不用提前预热 engine。

不过不建议这样做,因为按需创建FlutterEngine 的话,在 FlutterViewController 被 present 出来之后,第一帧图像渲染完之前,将会引入明显的延迟。但是当 Flutter 页面很少被展示时,当对决定何时启动 Dart VM 没有好的启发时,当 Flutter 无需在页面(view controller)之间保持状态时,此方式可能会有用。

为了不使用已经存在的 FlutterEngine 来展现 FlutterViewController,省略 FlutterEngine 的创建步骤,并且在创建 FlutterViewController 时,去掉 engine 的引用。

// Existing code omitted.
func showFlutter() {
  let flutterViewController = FlutterViewController(project: nil, nibName: nil, bundle: nil)
  present(flutterViewController, animated: true, completion: nil)
}
// Existing code omitted.
// 省略已经存在的代码
- (void)showFlutter {
  FlutterViewController *flutterViewController =
      [[FlutterViewController alloc] initWithProject:nil nibName:nil bundle:nil];
  [self presentViewController:flutterViewController animated:YES completion:nil];
}
@end

查看 加载顺序和性能 了解更多关于延迟和内存使用的探索。

使用 FlutterAppDelegate

推荐让你应用的 UIApplicationDelegate 继承 FlutterAppDelegate,但不是必须的。

FlutterAppDelegate 有这些功能:

  • 传递应用的回调,例如 openURL 到 Flutter 的插件 —— local_auth

  • 传递状态栏点击(这只能在 AppDelegate 中检测)到 Flutter 的点击置顶行为。

如果你的 app delegate 不能直接继承 FlutterAppDelegate,让你的 app delegate 实现 FlutterAppLifeCycleProvider 协议,来确保 Flutter plugins 接收到必要的回调。否则,依赖这些事件的 plugins 将会有无法预估的行为。

例如:

@import Flutter;
@import UIKit;
@import FlutterPluginRegistrant;

@interface AppDelegate : UIResponder <UIApplicationDelegate, FlutterAppLifeCycleProvider>
@property (strong, nonatomic) UIWindow *window;
@property (nonatomic,strong) FlutterEngine *flutterEngine;
@end

在具体实现中,应该最大化地委托给 FlutterPluginAppLifeCycleDelegate

@interface AppDelegate ()
@property (nonatomic, strong) FlutterPluginAppLifeCycleDelegate* lifeCycleDelegate;
@end

@implementation AppDelegate

- (instancetype)init {
    if (self = [super init]) {
        _lifeCycleDelegate = [[FlutterPluginAppLifeCycleDelegate alloc] init];
    }
    return self;
}

- (BOOL)application:(UIApplication*)application
didFinishLaunchingWithOptions:(NSDictionary<UIApplicationLaunchOptionsKey, id>*))launchOptions {
    self.flutterEngine = [[FlutterEngine alloc] initWithName:@"io.flutter" project:nil];
    [self.flutterEngine runWithEntrypoint:nil];
    [GeneratedPluginRegistrant registerWithRegistry:self.flutterEngine];
    return [_lifeCycleDelegate application:application didFinishLaunchingWithOptions:launchOptions];
}

// Returns the key window's rootViewController, if it's a FlutterViewController.
// Otherwise, returns nil.
- (FlutterViewController*)rootFlutterViewController {
    UIViewController* viewController = [UIApplication sharedApplication].keyWindow.rootViewController;
    if ([viewController isKindOfClass:[FlutterViewController class]]) {
        return (FlutterViewController*)viewController;
    }
    return nil;
}

- (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
    [super touchesBegan:touches withEvent:event];

    // Pass status bar taps to key window Flutter rootViewController.
    if (self.rootFlutterViewController != nil) {
        [self.rootFlutterViewController handleStatusBarTouches:event];
    }
}

- (void)application:(UIApplication*)application
didRegisterUserNotificationSettings:(UIUserNotificationSettings*)notificationSettings {
    [_lifeCycleDelegate application:application
didRegisterUserNotificationSettings:notificationSettings];
}

- (void)application:(UIApplication*)application
didRegisterForRemoteNotificationsWithDeviceToken:(NSData*)deviceToken {
    [_lifeCycleDelegate application:application
didRegisterForRemoteNotificationsWithDeviceToken:deviceToken];
}

- (void)application:(UIApplication*)application
didReceiveRemoteNotification:(NSDictionary*)userInfo
fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler {
    [_lifeCycleDelegate application:application
       didReceiveRemoteNotification:userInfo
             fetchCompletionHandler:completionHandler];
}

- (BOOL)application:(UIApplication*)application
            openURL:(NSURL*)url
            options:(NSDictionary<UIApplicationOpenURLOptionsKey, id>*)options {
    return [_lifeCycleDelegate application:application openURL:url options:options];
}

- (BOOL)application:(UIApplication*)application handleOpenURL:(NSURL*)url {
    return [_lifeCycleDelegate application:application handleOpenURL:url];
}

- (BOOL)application:(UIApplication*)application
            openURL:(NSURL*)url
  sourceApplication:(NSString*)sourceApplication
         annotation:(id)annotation {
    return [_lifeCycleDelegate application:application
                                   openURL:url
                         sourceApplication:sourceApplication
                                annotation:annotation];
}

- (void)application:(UIApplication*)application
performActionForShortcutItem:(UIApplicationShortcutItem*)shortcutItem
  completionHandler:(void (^)(BOOL succeeded))completionHandler {
    [_lifeCycleDelegate application:application
       performActionForShortcutItem:shortcutItem
                  completionHandler:completionHandler];
}

- (void)application:(UIApplication*)application
handleEventsForBackgroundURLSession:(nonnull NSString*)identifier
  completionHandler:(nonnull void (^)(void))completionHandler {
    [_lifeCycleDelegate application:application
handleEventsForBackgroundURLSession:identifier
                  completionHandler:completionHandler];
}

- (void)application:(UIApplication*)application
performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult result))completionHandler {
    [_lifeCycleDelegate application:application performFetchWithCompletionHandler:completionHandler];
}

- (void)addApplicationLifeCycleDelegate:(NSObject<FlutterPlugin>*)delegate {
    [_lifeCycleDelegate addDelegate:delegate];
}
@end

启动选项

例子中展示了使用默认启动选项运行 Flutter。

为了定制化你的 Flutter 运行时,你也可以置顶 Dart 入口、库和路由。

Dart 入口

FlutterEngine 上调用 run,默认将会调用你的 lib/main.dart 文件里的 main() 函数。

你也可以使用另一个入口方法 runWithEntrypoint,并使用 NSString 字符串指定一个不同的 Dart 入口。

Dart 库

另外,在指定 Dart 函数时,你可以指定特定文件的特定函数。

下面的例子使用 lib/other_file.dart 文件的 myOtherEntrypoint() 函数取代 lib/main.dartmain() 函数:

flutterEngine.run(withEntrypoint: "myOtherEntrypoint", libraryURI: "other_file.dart")
[flutterEngine runWithEntrypoint:@"myOtherEntrypoint" libraryURI:@"other_file.dart"];

路由

当构建 engine 时,可以为你的 Flutter WidgetsApp 设置一个初始路由。

let flutterEngine = FlutterEngine(name: "my flutter engine")
flutterEngine.navigationChannel.invokeMethod("setInitialRoute", arguments:"/onboarding")
flutterEngine.run()
FlutterEngine *flutterEngine = [[FlutterEngine alloc] init];
// FlutterDefaultDartEntrypoint is the same as nil, which will run main().
[flutterEngine runWithEntrypoint:FlutterDefaultDartEntrypoint
                    initialRoute:@"/onboarding"];

这段代码使用 "/onboarding" 取代 "/",作为你的 dart:uiwindow.defaultRouteName

let flutterViewController = FlutterViewController(
      project: nil, initialRoute: "/onboarding", nibName: nil, bundle: nil)
FlutterViewController* flutterViewController =
      [[FlutterViewController alloc] initWithProject:nil
                                        initialRoute:@"/onboarding"
                                             nibName:nil
                                              bundle:nil];

查看文档:路由和导航 了解更多 Flutter 路由的内容。

其它

之前的例子仅仅展示了怎样定制 Flutter 实例初始化的几种方式,通过 撰写双端平台代码,你可以在 FlutterViewController 展示 Flutter UI 之前,自由地选择你喜欢的,推入数据和准备 Flutter 环境的方式。 The previous example only illustrates a few ways to customize how a Flutter instance is initiated. Using platform channels, you’re free to push data or prepare your Flutter environment in any way you’d like, before presenting the Flutter UI using a FlutterViewController.