iOS集成Flutter使用FlutterEngine来降低内存使用

要使用Flutter，就必须iOS项目加入Flutter。

然后iOS与Flutter相互通信，在跳转多次跳转Flutter之后，发现iOS使用内存每次升50～～60M内存，这样子经过多次跳转势必会造成iOS闪退，不利于开发。

下面我们看下由iOS与Flutter相互通信的交互视频，来看下每次跳转的内存上升。

neicun_up.gif

怎么能够降低这个内存使用呢？这里我们就使用FlutterEngine来保证跳转flutter的时候内存稳定在50～～60M。

首先，要先声明FlutterEngine对象：

//声明FlutterEngine对象
@property (nonatomic, strong) FlutterEngine *flutterEngin;

然后，实现FlutterEngine兑现的懒加载：

#pragma mark -- Lazy method
- (FlutterEngine *)flutterEngin {
    if (nil == _flutterEngin) {
        FlutterEngine *flutterEngin = [[FlutterEngine alloc] initWithName:@"flutter_native" project:nil];
        [flutterEngin runWithEntrypoint:nil];
        [GeneratedPluginRegistrant registerWithRegistry:flutterEngin];
        _flutterEngin = flutterEngin;
    }
    return _flutterEngin;
}

接下来，声明一个btn，通过这个btn使用FlutterEngine跳转进Flutter页面，只要使用了FlutterEngine来进行跳转，不管跳转多少次，内存都只会增长一次。

要使用FlutterEngine就需要在声明FlutterViewController的时候使用FlutterEngine，然后再声明FlutterMethodChannel和FlutterEventChannel来实现原生和flutter的双向通信，详细代码如下：

/**
 使用FlutterEngine跳转Flutter
 */
- (IBAction)use_flutter_engin_btn_click:(id)sender {
    FlutterViewController *flvc = [[FlutterViewController alloc] initWithEngine:self.flutterEngin nibName:nil bundle:nil];
    //单项通信管道，Flutter向原生发送消息
    FlutterMethodChannel *messageChannel = [FlutterMethodChannel methodChannelWithName:@"com.flutterToNative" binaryMessenger:flvc];
    __weak typeof(self) weakSelf = self;
    [messageChannel setMethodCallHandler:^(FlutterMethodCall * _Nonnull call, FlutterResult  _Nonnull result) {
        if ([@"backToNative" isEqualToString:call.method]) {
            [weakSelf dismissViewControllerAnimated:true completion:nil];
        }
    }];
    
    //单项通信管道，原生向Flutter发送消息
    FlutterEventChannel *eventChannel = [FlutterEventChannel eventChannelWithName:@"com.nativeToFlutter" binaryMessenger:flvc];
    [eventChannel setStreamHandler:self];
    
    [self presentViewController:flvc animated:true completion:nil];
}


#pragma mark -- FlutterStreamHandler代理
- (FlutterError* _Nullable)onListenWithArguments:(id _Nullable)arguments
                                       eventSink:(FlutterEventSink)events {
    if (events) {
        self.eventSink  = events;
        self.eventSink(@"从原生传递过来的消息。。。。。。。");
    }
    return nil;
}
// 不再需要向Flutter传递消息
- (FlutterError* _Nullable)onCancelWithArguments:(id _Nullable)arguments {
    return nil;
}

#pragma mark -- Lazy method
- (FlutterEngine *)flutterEngin {
    if (nil == _flutterEngin) {
        FlutterEngine *flutterEngin = [[FlutterEngine alloc] initWithName:@"flutter_native" project:nil];
        [flutterEngin runWithEntrypoint:nil];
        [GeneratedPluginRegistrant registerWithRegistry:flutterEngin];
        _flutterEngin = flutterEngin;
    }
    return _flutterEngin;
}

最后看一下运行起来的效果：

flutterEngin_demo.gif

从运行结果可以看出，运行内存在第一次跳转到flutter页面升高之后，后续就相对于稳定。

至于为什么在跳转flutter的时候内存会猛的增高，这是因为FlutterEngine对象在跳转完Flutter再回到iOS的时候，FlutterEngine没有释放掉，是google关于Flutter对iOS支持的一个bug，希望后续这个问题会在存在。

到这里就实现了单引擎使用FlutterEngine来稳定内存的实现，后续各位在实现的时候，可以把FlutterEngine声明在AppDelegate.h文件中，或者专门声明一个FlutterManager的单利来实现整个iOS系统内只有一份FlutterEngine。