向 iOS 應用新增 Flutter 螢幕
瞭解如何將單個 Flutter 螢幕新增到現有的 iOS 應用中。
本指南介紹瞭如何將單個 Flutter 螢幕新增到現有的 iOS 應用中。
啟動 FlutterEngine 和 FlutterViewController
#要從現有的 iOS 應用啟動 Flutter 螢幕，你需要啟動一個 FlutterEngine 和一個 FlutterViewController。
FlutterEngine 的生命週期可以與 FlutterViewController 相同，也可以比 FlutterViewController 更長。
關於預熱引擎的延遲和記憶體權衡的更多分析，請參閱載入順序與效能。
建立 FlutterEngine
#在哪裡建立 FlutterEngine 取決於你的宿主應用。
在此示例中，我們在一個名為 FlutterDependencies 的 SwiftUI Observable 物件內部建立了一個 FlutterEngine 物件。透過呼叫 run() 來預熱引擎，然後使用 environment() 檢視修飾符將此物件注入 ContentView。
MyApp.swift
swift
import SwiftUI
import Flutter
// The following library connects plugins with iOS platform code to this app.
import FlutterPluginRegistrant
@Observable
class FlutterDependencies {
let flutterEngine = FlutterEngine(name: "my flutter engine")
init() {
// Runs the default Dart entrypoint with a default Flutter route.
flutterEngine.run()
// Connects plugins with iOS platform code to this app.
GeneratedPluginRegistrant.register(with: self.flutterEngine);
}
}
@main
struct MyApp: App {
// flutterDependencies will be injected through the view environment.
@State var flutterDependencies = FlutterDependencies()
var body: some Scene {
WindowGroup {
ContentView()
.environment(flutterDependencies)
}
}
}
作為示例，我們演示瞭如何在應用啟動時的應用代理（app delegate）中建立一個作為屬性暴露的 FlutterEngine。
AppDelegate.swift
swift
import UIKit
import Flutter
// The following library connects plugins with iOS platform code to this app.
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();
// Connects plugins with iOS platform code to this app.
GeneratedPluginRegistrant.register(with: self.flutterEngine);
return super.application(application, didFinishLaunchingWithOptions: launchOptions);
}
}
以下示例演示瞭如何在應用啟動時的應用代理中建立一個作為屬性暴露的 FlutterEngine。
AppDelegate.h
objc
@import UIKit;
@import Flutter;
@interface AppDelegate : FlutterAppDelegate // More on the FlutterAppDelegate below.
@property (nonatomic,strong) FlutterEngine *flutterEngine;
@end
AppDelegate.m
objc
// The following library connects plugins with iOS platform code to this app.
#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];
// Connects plugins with iOS platform code to this app.
[GeneratedPluginRegistrant registerWithRegistry:self.flutterEngine];
return [super application:application didFinishLaunchingWithOptions:launchOptions];
}
@end
使用 FlutterEngine 展示 FlutterViewController
#以下示例展示了一個帶有 NavigationLink 並連線到 Flutter 螢幕的通用 ContentView。首先，建立一個 FlutterViewControllerRepresentable 來表示 FlutterViewController。FlutterViewController 建構函式將預熱後的 FlutterEngine 作為引數，該引數透過檢視環境進行注入。
ContentView.swift
swift
import SwiftUI
import Flutter
struct FlutterViewControllerRepresentable: UIViewControllerRepresentable {
// Flutter dependencies are passed in through the view environment.
@Environment(FlutterDependencies.self) var flutterDependencies
func makeUIViewController(context: Context) -> some UIViewController {
return FlutterViewController(
engine: flutterDependencies.flutterEngine,
nibName: nil,
bundle: nil)
}
func updateUIViewController(_ uiViewController: UIViewControllerType, context: Context) {}
}
struct ContentView: View {
var body: some View {
NavigationStack {
NavigationLink("My Flutter Feature") {
FlutterViewControllerRepresentable()
}
}
}
}
現在，你已將一個 Flutter 螢幕嵌入到你的 iOS 應用中。
以下示例展示了一個帶有 UIButton 並連線到展示 FlutterViewController 的通用 ViewController。FlutterViewController 使用了在 AppDelegate 中建立的 FlutterEngine 例項。
ViewController.swift
swift
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)
}
}
現在，你已將一個 Flutter 螢幕嵌入到你的 iOS 應用中。
以下示例展示了一個帶有 UIButton 並連線到展示 FlutterViewController 的通用 ViewController。FlutterViewController 使用了在 AppDelegate 中建立的 FlutterEngine 例項。
ViewController.m
objc
@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
現在，你已將一個 Flutter 螢幕嵌入到你的 iOS 應用中。
替代方案 - 使用隱式 FlutterEngine 建立 FlutterViewController
#作為前一個示例的替代方案，你可以讓 FlutterViewController 隱式建立其自身的 FlutterEngine，而無需提前預熱。
通常不建議這樣做，因為按需建立 FlutterEngine 可能會在展示 FlutterViewController 和渲染第一幀之間引入明顯的延遲。但是，如果 Flutter 螢幕很少顯示，或者沒有很好的啟發式方法來確定何時啟動 Dart 虛擬機器，且 Flutter 不需要跨檢視控制器持久化狀態時，這可能會很有用。
要讓 FlutterViewController 在沒有現有 FlutterEngine 的情況下呈現，請忽略 FlutterEngine 的構建，並在沒有引擎引用的情況下建立 FlutterViewController。
ContentView.swift
swift
import SwiftUI
import Flutter
struct FlutterViewControllerRepresentable: UIViewControllerRepresentable {
func makeUIViewController(context: Context) -> some UIViewController {
return FlutterViewController(
project: nil,
nibName: nil,
bundle: nil)
}
func updateUIViewController(_ uiViewController: UIViewControllerType, context: Context) {}
}
struct ContentView: View {
var body: some View {
NavigationStack {
NavigationLink("My Flutter Feature") {
FlutterViewControllerRepresentable()
}
}
}
}
ViewController.swift
swift
// Existing code omitted.
func showFlutter() {
let flutterViewController = FlutterViewController(project: nil, nibName: nil, bundle: nil)
present(flutterViewController, animated: true, completion: nil)
}
ViewController.m
objc
// Existing code omitted.
- (void)showFlutter {
FlutterViewController *flutterViewController =
[[FlutterViewController alloc] initWithProject:nil nibName:nil bundle:nil];
[self presentViewController:flutterViewController animated:YES completion:nil];
}
@end
有關延遲和記憶體使用的更多探索，請參閱載入順序與效能。
使用 FlutterAppDelegate
#建議但不強制要求讓應用的 UIApplicationDelegate 繼承 FlutterAppDelegate。
FlutterAppDelegate 執行的功能包括：
- 將
openURL等應用回撥轉發給 local_auth 等外掛。 - 在除錯模式下，手機螢幕鎖定後保持 Flutter 連線處於開啟狀態。
建立 FlutterAppDelegate 子類
#在 UIKit 應用中建立 FlutterAppDelegate 的子類已在啟動 FlutterEngine 和 FlutterViewController 章節中展示。在 SwiftUI 應用中，你可以建立一個 FlutterAppDelegate 的子類，並使用 Observable() 宏進行註解，如下所示：
MyApp.swift
swift
import SwiftUI
import Flutter
import FlutterPluginRegistrant
@Observable
class AppDelegate: FlutterAppDelegate {
let 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 true;
}
}
@main
struct MyApp: App {
// Use this property wrapper to tell SwiftUI
// it should use the AppDelegate class for the application delegate
@UIApplicationDelegateAdaptor(AppDelegate.self) var appDelegate
var body: some Scene {
WindowGroup {
ContentView()
}
}
}
然後，在你的檢視中，可以透過檢視環境訪問 AppDelegate。
ContentView.swift
swift
import SwiftUI
import Flutter
struct FlutterViewControllerRepresentable: UIViewControllerRepresentable {
// Access the AppDelegate through the view environment.
@Environment(AppDelegate.self) var appDelegate
func makeUIViewController(context: Context) -> some UIViewController {
return FlutterViewController(
engine: appDelegate.flutterEngine,
nibName: nil,
bundle: nil)
}
func updateUIViewController(_ uiViewController: UIViewControllerType, context: Context) {}
}
struct ContentView: View {
var body: some View {
NavigationStack {
NavigationLink("My Flutter Feature") {
FlutterViewControllerRepresentable()
}
}
}
}
如果無法直接繼承 FlutterAppDelegate
#如果你的應用代理無法直接繼承 FlutterAppDelegate，請讓你的應用代理實現 FlutterAppLifeCycleProvider 協議，以確保你的外掛接收到必要的回撥。否則，依賴這些事件的外掛可能會出現未定義的行為。
例如：
AppDelegate.swift
swift
import Foundation
import Flutter
@Observable
class AppDelegate: UIResponder, UIApplicationDelegate, FlutterAppLifeCycleProvider {
private let lifecycleDelegate = FlutterPluginAppLifeCycleDelegate()
let flutterEngine = FlutterEngine(name: "my flutter engine")
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
flutterEngine.run()
return lifecycleDelegate.application(application, didFinishLaunchingWithOptions: launchOptions ?? [:])
}
func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {
lifecycleDelegate.application(application, didRegisterForRemoteNotificationsWithDeviceToken: deviceToken)
}
func application(_ application: UIApplication, didFailToRegisterForRemoteNotificationsWithError error: Error) {
lifecycleDelegate.application(application, didFailToRegisterForRemoteNotificationsWithError: error)
}
func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any], fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
lifecycleDelegate.application(application, didReceiveRemoteNotification: userInfo, fetchCompletionHandler: completionHandler)
}
func application(_ app: UIApplication, open url: URL, options: [UIApplication.OpenURLOptionsKey : Any] = [:]) -> Bool {
return lifecycleDelegate.application(app, open: url, options: options)
}
func application(_ application: UIApplication, handleOpen url: URL) -> Bool {
return lifecycleDelegate.application(application, handleOpen: url)
}
func application(_ application: UIApplication, open url: URL, sourceApplication: String?, annotation: Any) -> Bool {
return lifecycleDelegate.application(application, open: url, sourceApplication: sourceApplication ?? "", annotation: annotation)
}
func application(_ application: UIApplication, performActionFor shortcutItem: UIApplicationShortcutItem, completionHandler: @escaping (Bool) -> Void) {
lifecycleDelegate.application(application, performActionFor: shortcutItem, completionHandler: completionHandler)
}
func application(_ application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: @escaping () -> Void) {
lifecycleDelegate.application(application, handleEventsForBackgroundURLSession: identifier, completionHandler: completionHandler)
}
func application(_ application: UIApplication, performFetchWithCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
lifecycleDelegate.application(application, performFetchWithCompletionHandler: completionHandler)
}
func add(_ delegate: FlutterApplicationLifeCycleDelegate) {
lifecycleDelegate.add(delegate)
}
}
AppDelegate.h
objc
@import Flutter;
@import UIKit;
@import FlutterPluginRegistrant;
@interface AppDelegate : UIResponder <UIApplicationDelegate, FlutterAppLifeCycleProvider>
@property (strong, nonatomic) UIWindow *window;
@property (nonatomic,strong) FlutterEngine *flutterEngine;
@end
實現應主要委託給 FlutterPluginAppLifeCycleDelegate
AppDelegate.m
objc
@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)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
啟動選項
#以上示例演示了使用預設啟動設定執行 Flutter。
為了自定義 Flutter 執行時，你還可以指定 Dart 入口點、庫和路由。
Dart 入口點
#預設情況下，對 FlutterEngine 呼叫 run 會執行 lib/main.dart 檔案中的 main() Dart 函式。
你也可以使用 runWithEntrypoint 並配合指定不同 Dart 函式的 NSString 來執行不同的入口點函式。
Dart 庫
#除了指定 Dart 函式外，你還可以指定特定檔案中的入口點函式。
例如，以下程式碼執行 lib/other_file.dart 中的 myOtherEntrypoint()，而不是 lib/main.dart 中的 main()。
swift
flutterEngine.run(withEntrypoint: "myOtherEntrypoint", libraryURI: "other_file.dart")
objc
[flutterEngine runWithEntrypoint:@"myOtherEntrypoint" libraryURI:@"other_file.dart"];
Route
#從 Flutter 1.22 版本開始，可以在構建 FlutterEngine 或 FlutterViewController 時為 Flutter WidgetsApp 設定初始路由。
swift
let flutterEngine = FlutterEngine()
// FlutterDefaultDartEntrypoint is the same as nil, which will run main().
engine.run(
withEntrypoint: "main", initialRoute: "/onboarding")
objc
FlutterEngine *flutterEngine = [[FlutterEngine alloc] init];
// FlutterDefaultDartEntrypoint is the same as nil, which will run main().
[flutterEngine runWithEntrypoint:FlutterDefaultDartEntrypoint
initialRoute:@"/onboarding"];
此程式碼將 dart:ui 的 PlatformDispatcher.defaultRouteName 設定為 "/onboarding"，而不是 "/"。
或者，直接構建 FlutterViewController 而無需預熱 FlutterEngine：
swift
let flutterViewController = FlutterViewController(
project: nil, initialRoute: "/onboarding", nibName: nil, bundle: nil)
objc
FlutterViewController* flutterViewController =
[[FlutterViewController alloc] initWithProject:nil
initialRoute:@"/onboarding"
nibName:nil
bundle:nil];
有關 Flutter 路由的更多資訊，請參閱導航與路由。
其他
#前面的示例僅展示了啟動 Flutter 例項的幾種方法。使用平臺通道，你可以在使用 FlutterViewController 展示 Flutter UI 之前，以任何你喜歡的方式推送資料或準備 Flutter 環境。
內容自適應檢視
#在 iOS 上，你還可以將嵌入的 FlutterView 設定為根據其內容自動調整大小。
swift
let flutterViewController = FlutterViewController(engine: engine, nibName: nil, bundle: nil)
flutterViewController.isAutoResizable = true
objc
_flutterViewController = [[FlutterViewController alloc] initWithEngine:engine nibName:nil bundle:nil];
_flutterViewController.autoResizable = YES;
限制
#要使用此功能，你的根小部件必須支援無邊界約束。避免在樹的頂部使用需要有邊界約束的小部件（如 ListView 或 LayoutBuilder），因為它們可能會與動態調整大小邏輯衝突。
實際上，這意味著許多常見的小部件是不支援的，例如 ScaffoldBuilder、CupertinoTimerPicker 或任何內部依賴 LayoutBuilder 的小部件。如果有疑問，你可以使用 UnconstrainedBox 來測試小部件對於內容自適應檢視的可用性，如下例所示：
dart
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context)
=> MaterialApp(home: MyPage());
}
class MyPage extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
body: UnconstrainedBox(
// TODO: Edit this line to check if a widget
// can cause problems with content-sized views.
child: Text('This works!'),
// child: Column(children: [Column(children: [Expanded(child: Text('This blows up!'))])]),
// child: ListView(children: [Text('This blows up!')]),
)
);
}
}
有關可執行的示例，請參閱此示例專案。