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。
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：
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。
