由于flutter一直存在内存泄漏的问题，导致很多开发者不胜困扰，博主在0.9.4就开始对其代码内部内存问题在engine层面修改代码，得到解决，但是对于每个版本都需要跟随官方打包,对于开发者并不是很友好。
然而喜出望外的是，在后来的几个版本中，官方内置开发了手动释放内存的方式:smile_cat:
/** * Destroy running context for an engine. * * This method can be used to force the FlutterEngine object to release all resources. * After sending this message,the object will be in an unusable state until it is deallocated. * Accessing properties or sending messages to it will result in undefined behavior or runtime * errors. */ - (void)destroyContext;
翻译如下：
销毁引擎的运行上下文。 此方法可用于强制FlutterEngine对象释放所有资源。 发送此消息后，对象将处于不可用状态，直到解除分配为止。 访问属性或向其发送消息将导致未定义的行为或运行时错误。
但是,但是,但是 ，(重要的事说三遍) 在Flutter engine开发群里面，有群友反馈还有很多问题
- 无法完全释放内存
- 偶现崩溃
偶现崩溃的是什么鬼，暂时没有遇到，不好说。 之前博主遇到的崩溃是自己使用方式的问题，在fluttervc关闭之后还有任务在执行methodchannel，即还在调用plugin，这个可以在开发上避免。 值得注意的是，flutter中使用c++实现，自己对于内存管理并不是很好
内存问题自测如下
确实存在问题，还有将近30M没有被释放，查看一下当前内存对象，如下图
一个一个看还有那些没有被释放吧
android:LruCache
Least Recently Used 近期最少使用算法。 内存管理的一种页面置换算法，对于在内存中但又不用的数据块（内存块）叫做LRU，flutter engine 会根据哪些数据属于LRU而将其移出内存而腾出空间来加载另外的数据。
dart::BackgroundComplier 对isolate编译优化的类
BackgroundCompiler 在后台线程中运行优化编译的类。 实现：每个隔离一个任务，它与拥有isolate一起消失，后台编译器中没有OSR编译。
dart::bin::socket
vm和开发平台通信的机制，比如jit即时编译的dill文件，通过socket传递给dart vm，vm通过rpc加载文件，重置线程，从而实现hotreload热重载
dart::BoolPrameter
- dart::EnumParameter
- dart::IdParameter
- dart::IdParameter
- dart::xxxPrameter
定义在dart vm，service.cc中，都继承自MethodParameter，做对应参数校验，参数解析用。编译dart文件用的
dart::OSThread
在dart 运行时负责操作系统线程，创建线程，移除线程，线程查找与管理。 如下图
FlutterEngineRegistrar 注册使用key注册plugin的地方，所有plugin调用dart底层的方法都会通过 handlemethodcall 回调给使用者， 其初始化的地方是引起内存泄漏的地方
- (instancetype)initWithPlugin:(NSString*)pluginKey flutterEngine:(FlutterEngine*)flutterEngine {
self = [super init];
NSAssert(self,@"Super init cannot be nil");
_pluginKey = pluginKey;// [pluginKey retain];
_flutterEngine = flutterEngine;// [flutterEngine retain];
return self;
}
FlutterStandardMethodCodec 标准方法编解码
FlutterStringCodec string编解码 FlutterJsonMessageCodec json编解码
不看不知道，一看吓一跳，也竟然是个单例，当然不会被释放了，也能理解，在flutter中用到jsonmssage的地方很多，用不着每次都初始化
代码实现的地方
@implementation FlutterJSONMessageCodec
+ (instancetype)sharedInstance {
static id _sharedInstance = nil;
if (!_sharedInstance) {
_sharedInstance = [FlutterJSONMessageCodec new];
}
return _sharedInstance;
}
std:share_ptrxxx 共享指针
指针获取 flutter isolate service dartvm symbolmapping
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完整测试代码如下
#import "FlutterTesterViewController.h"
#import <Flutter/Flutter.h>
#import "GeneratedPluginRegistrant.h"
@interface FlutterTesterViewController ()
@property (nonatomic,weak) FlutterViewController * ctr;
@property (nonatomic,weak) FlutterEngine * engine;
@end
@implementation FlutterTesterViewController
- (void)viewDidLoad {
[super viewDidLoad];
float Y = 210;
[self createButton:@"加载boundle资源" frame:CGRectMake(80.0,Y,160.0,40.0) action:@selector(handleBoundleResource )];
Y += 40.0 + 10;
[self createButton:@"autorelease" frame:CGRectMake(80.0,40.0) action:@selector(handleAutoRelase)];
NSArray * paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask,YES);
NSString * path = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"flutter_assets"] ;
NSLog(@"path: %@",path);
}
-(void)handleNetWorkResource:(UIButton *)button{
}
/**
* 加载boundle资源
*/
- (void)handleBoundleResource {
FlutterDartProject * dart = [[FlutterDartProject alloc] init];
FlutterEngine * engine = [[FlutterEngine alloc] initWithName:@"ios.dart.flutter"
project:dart];
[engine runWithEntrypoint:nil];
FlutterViewController* flutterViewController = [[FlutterViewController alloc] initWithEngine:engine nibName:nil bundle:nil];
[GeneratedPluginRegistrant registerWithRegistry:flutterViewController];
[self addBackButton:flutterViewController];
[flutterViewController setInitialRoute:@"route1"];
[self presentViewController:flutterViewController animated:YES completion:nil];
self.engine = engine;
}
-(void)handleAutoRelase{
FlutterBasicMessageChannel* channel;
FlutterEngine * engine;
@autoreleasepool {
FlutterViewController* flutterViewController =
[[FlutterViewController alloc] init];
channel = flutterViewController.engine.systemChannel;
engine = flutterViewController.engine;
NSLog(@"engine111:%@",engine);
}
NSLog(@"engine222:%@",engine);
[channel sendMessage:@"Hello!"];
[channel setMessageHandler:^(id _Nullable message,FlutterReply _Nonnull callback) { }];
}
-(void)addBackButton:(UIViewController *)flutterViewController{
dispatch_after(dispatch_time(DISPATCH_TIME_NOW,(int64_t)(2 * NSEC_PER_SEC)),dispatch_get_main_queue(),^{
UIButton * btn = [UIButton buttonWithType:UIButtonTypeSystem];
[btn setTitle:@"关闭" forState:UIControlStateNormal];
btn.frame = CGRectMake(10,100,50,30);
[btn addTarget:self action:@selector(buttonTap:) forControlEvents:UIControlEventTouchUpInside];
[flutterViewController.view addSubview:btn];
self.ctr = flutterViewController;
});
}
-(void)buttonTap:(id)sender{
// [self.navigationController popViewControllerAnimated:YES];
__weak __typeof(self)weakSelf = self;
[self.ctr dismissViewControllerAnimated:YES completion:^{
[weakSelf.engine destroyContext];
}];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
-(UIButton *)createButton:(NSString *)title frame:(CGRect)frame action:(SEL)selector{
UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
[button addTarget:self
action:selector
forControlEvents:UIControlEventTouchUpInside];
[button setTitle:title forState:UIControlStateNormal];
UIColor * bgcolor = [UIColor colorWithRed:arc4random()%256/255. green:arc4random()%256/255. blue:arc4random()%256/255. alpha:1];
[button setBackgroundColor:bgcolor];
button.frame = frame;
[self.view addSubview:button];
return button;
}
@end