iOS 视图控制器的内存申请与释放普遍规则

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,获取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

.Example:　　

myController = [[*** alloc] initWithNibName:"***" bundle:nil];

UINavigationController *navi = [[UINavigationController alloc] initWithRootViewController:myController];

[myController release];

[tabController presentModalViewController:navi animated:YES];

[navi release];

-(void) dealloc

{

[myController release]

[tabController release];

[supper dealloc];

}

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;

}