Flutter iOS之间通信
1.Flutter架构
flutter架构.png
Flutter框架包括：Framework和Engine，他们运行在各自的Platform上。
Framework是Dart语言开发的，包括Material Design风格的Widgets和Cupertino(iOS-style)风格的Widgets，以及文本、图片、按钮等基础Widgets；还包括渲染、动画、绘制、手势等基础能力。
Engine是C++实现的，包括Skia（二维图形库）；Dart VM（Dart Runtime）；Text（文本渲染）等。
实际上，Flutter的上层能力都是Engine提供的。Flutter正是通过Engine将各个Platform的差异化抹平。而我们今天要讲的Flutter 与 Native之间的通信，正是通过Engine提供的Platform Channel实现的。
2. Platform Channel
2.1 Flutter App调用Native APIs：
flutter调用Native API.png
通过上图，我们看到Flutter App是通过Platform Channel调用的Native APIs。
2.2Platform Channel 架构图：
Platform Channel 架构图.png
Platform Channel：
- Flutter App (Client)，通过MethodChannel类向Platform发送调用消息；
- iOS Platform (Host)，通过FlutterMethodChannel类接收调用消息。
PS：消息编解码器，是JSON格式的二进制序列化，所以调用方法的参数类型必须是可JSON序列化的
PS：方法调用，也可以反向发送调用消息。
3.Flutter部分
3.1MethodChannel：Flutter App调用Native APIs
/**
* （1）MethodChannel：Flutter App调用Native APIs
*/
static const MethodChannel _methodChannel = const MethodChannel('samples.flutter.io/battery');
//
Future<String> getBatteryLevel() async {
String batteryLevel;
try {
final int result = await _methodChannel.invokeMethod('getBatteryLevel',{'paramName':'paramVale'});
batteryLevel = 'Battery level: $result%.';
} catch(e) {
batteryLevel = 'Failed to get battery level.';
}
return batteryLevel;
}
首先，我们实例_methodChannel(Channel名称必须唯一)，然后调用invokeMethod()方法。invokeMethod()有2个参数：
（1）方法名，不能为空；
（2）调用方法的参数，该参数必须可JSON序列化，可以为空。
3.2EventChannel：Native调用Flutter App
/**
* （2）EventChannel：Native调用Flutter App
*/
static const EventChannel _eventChannel = const EventChannel('samples.flutter.io/charging');
void listenNativeEvent() {
_eventChannel.receiveBroadcastStream().listen(_onEvent, onError:_onError);
}
void _onEvent(dynamic event) {
print("Battery status: ${event == 'charging' ? '' : 'dis'}charging.");
}
void _onError(Object error) {
print('Battery status: unknown.');
}
4.iOS端实现
/**
* Channel名称：必须与Flutter App的Channel名称一致
*/
#define METHOD_CHANNEL "samples.flutter.io/battery";
#define EVENT_CHANNEL "samples.flutter.io/charging";
@implementation AppDelegate
- (BOOL)application:(UIApplication*)application didFinishLaunchingWithOptions:(NSDictionary*)launchOptions {
/**
* FlutterViewController
*/
FlutterViewController* controller = (FlutterViewController*)self.window.rootViewController;
/**
* FlutterMethodChannel & Handler
*/
FlutterMethodChannel* batteryChannel = [FlutterMethodChannel methodChannelWithName:METHOD_CHANNEL binaryMessenger:controller];
[batteryChannel setMethodCallHandler:^(FlutterMethodCall* call, FlutterResult result) {
if ([@"getBatteryLevel" isEqualToString:call.method]) {
int batteryLevel = [self getBatteryLevel];
result(@(batteryLevel));
} else {
result(FlutterMethodNotImplemented);
}
}];
/**
* FlutterEventChannel & Handler
*/
FlutterEventChannel* chargingChannel = [FlutterEventChannel eventChannelWithName:EVENT_CHANNEL binaryMessenger:controller];
[chargingChannel setStreamHandler:self];
return [super application:application didFinishLaunchingWithOptions:launchOptions];
}
@end
（1）Channel名称：必须与Flutter App的Channel名称一致；
（2）FlutterMethodChannel和FlutterEventChannel初始化的时候都需要传递binaryMessenger，即FlutterViewController；
（3）设置FlutterMethodChannel的Handler；
（4）设置FlutterEventChannel的Handler；
3.4.2 FlutterStreamHandler：
@interface AppDelegate () <FlutterStreamHandler>
@property (nonatomic, copy) FlutterEventSink eventSink;
@end
- (FlutterError*)onListenWithArguments:(id)arguments eventSink:(FlutterEventSink)eventSink {
self.eventSink = eventSink;
// 监听电池状态
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(onBatteryStateDidChange:)
name:UIDeviceBatteryStateDidChangeNotification
object:nil];
return nil;
}
- (FlutterError*)onCancelWithArguments:(id)arguments {
[[NSNotificationCenter defaultCenter] removeObserver:self];
self.eventSink = nil;
return nil;
}
- (void)onBatteryStateDidChange:(NSNotification*)notification {
if (self.eventSink == nil) return;
UIDeviceBatteryState state = [[UIDevice currentDevice] batteryState];
switch (state) {
case UIDeviceBatteryStateFull:
case UIDeviceBatteryStateCharging:
self.eventSink(@"charging");
break;
case UIDeviceBatteryStateUnplugged:
self.eventSink(@"discharging");
break;
default:
self.eventSink([FlutterError errorWithCode:@"UNAVAILABLE"
message:@"Charging status unavailable"
details:nil]);
break;
}
}
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