小记 iOS 视图控制器的内存申请与释放普遍规则

作者:不及格的程序员-八神

内存管理在iOS程序开发扮演非常重要角色,对这块处理不好的程序会在实际设备上发生Crash情况.
对于经常在视图控制器中用retain声名的输出口一定要注意,在dealloc中release它们.
Obj-C声明的属性,具有如下特性,将新对象赋值当前属性,并自动释放属性中的旧对象.

1. 在appDelegate.m中如果有一个window输出口,或者另外加了一个导航视图控制器或是其它什么视图控制器时,在 dealloc 方法中,执行这些输出口的release方法.而不必在applicationDidFinishLaunching中执行释放.
2. 在单独的自定义视图控制器中,如果在接到内存紧缺通知时,会执行didReceiveMemoryWarning方法,它会卸载当前视图窗体,并执行viewDidUnload方法,所以在该方法中将方视图中的定义的输出口置为nil. 同时在该视图的dealloc方法(当该视图控件器的release被调用时,该方法被执行)中执行相应的输出口release方法.  

   -(void)viewDidUnload
   {
       self.** = nil;
   }
   
   -(void)dealloc
   {
       [** release];
       [supper dealloc];
   }

3. 实例方法,静态方法,工厂方法返回的对象的释方规则,后两者都不必手动执行release方法,由系统的内存池自动维护.
4. 如果我在appDelegate.m文件中alloc并init一个视图控制器,然后把它通过导航控制器的initWithRootViewController方法加到其中时,那么加完之后要释放那个视图控制器.Example:　　
   

   myController = [[*** alloc] initWithNibName:"***" bundle:nil];
   UINavigationController *navi = [[UINavigationController alloc] initWithRootViewController:myController];
   [myController release];
   [tabController presentModalViewController:navi animated:YES];
   [navi release];

5. 在自定义视图控制器中声明了变量,但是没定义相应属性,这时对象释放规则同第1条相同.

   @interface *** : UIViewController
   {
       UIView *_view;
   }
   @end
   
   @implementation ***
   -(void)loadView
   {
       [supper loadView];
       _view = [[UIView alloc] initWithFrame:[self.view bounds]];
       [self.view addSubview:_view];
   }
   
   -(void)dealloc
   {    
       [_view release];
       [supper dealloc];
   }
   @end

6. 在iPhone3开发基础教程中的样例切换视图的代码问题,我觉得里面有一个顺序写错了,之后我在google查了一下,有不少人有同问.
   

   @implementation SwitchViewController
   @synthesize blueViewController;
   @synthesize yellowViewController;
   
   - (void)viewDidLoad
   {
       BlueViewController *blueController = [[BlueViewController alloc] initWithNibName:@"BlueView" bundle:nil];
       self.blueViewController = blueController;
       [self.view insertSubview:blueController.view atIndex:0];
       [blueController release];
   }
   
   - (IBAction)switchViews:(id)sender
   {
       [UIView beginAnimations:@"View Flip" context:nil];
       [UIView setAnimationDuration:1.25];
       [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
       
       if (self.yellowViewController.view.superview == nil)//这条语句是最有趣的,OBJ-C允许向nil发送消息.
       {
           if (self.yellowViewController == nil)
           {
               YellowViewController *yellowController = 
               [[YellowViewController alloc] initWithNibName:@"YellowView" 
                                                      bundle:nil];
               self.yellowViewController = yellowController;
               [yellowController release];
           }
           [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight forView:self.view cache:YES];
           [blueViewController viewWillAppear:YES];
           [yellowViewController viewWillDisappear:YES];
           [blueViewController.view removeFromSuperview];
           [self.view insertSubview:yellowViewController.view atIndex:0];
           [yellowViewController viewDidDisappear:YES];
           [blueViewController viewDidAppear:YES];
       }
       else
       {
           if (self.blueViewController == nil)
           {
               BlueViewController *blueController = 
               [[BlueViewController alloc] initWithNibName:@"BlueView" 
                                                    bundle:nil];
               self.blueViewController = blueController;
               [blueController release];
           }
           //[UIView setAnimationTransition:
           // UIViewAnimationTransitionFlipFromLeft
           //                       forView:self.view cache:YES];
           
           //[yellowViewController viewWillAppear:YES];
           //[blueViewController viewWillDisappear:YES];
           [yellowViewController.view removeFromSuperview];
           [self.view insertSubview:blueViewController.view atIndex:0];
           //[blueViewController viewDidDisappear:YES];
           //[yellowViewController viewDidAppear:YES];
       }
       //[UIView commitAnimations];
   }
   
   
   - (void)didReceiveMemoryWarning 
   {
       [super didReceiveMemoryWarning]; 
       if (self.blueViewController.view.superview == nil) 
           self.blueViewController = nil;
       else
           self.yellowViewController = nil;
   }
   
   
   - (void)dealloc 
   {
       [yellowViewController release];
       [blueViewController release];
       [super dealloc];
   }
   
   @end

7.   都在dealloc中执行.我看到在wordPress的iPhone客户端这样做的,不过好像它在特意兼容iOS3之前的版本,3.0之前的版本并不存在viewDidUnload方法,苹果的开发手册上有描述.    

   -(void)dealloc
   {
       [myView release], myView = nil;
   }

   
   附.
   python /Users/yangiori/Downloads/facebook-three20-309d34e/src/scripts/ttmodule.py -p /Users/yangiori/Documents/iPhoneLiaoBao/iPhoneLiaoBao.xcodeproj Three20 //区分大小写。。。