AppDelegate.m(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];// Override point for customization after application launch.self.window.backgroundColor = [UIColor whiteColor];[self.window makeKeyAndVisible];   RootViewController *rootVC = [[RootViewController alloc] init];self.window.rootViewController = rootVC;[rootVC release];  return YES;
}

RootViewController.m

- (void)loadView {
//    self.view = [[UIView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];self.view = [[LoginView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];NSLog(@"加载视图");
}

视图已经加载完成
- (void)viewDidLoad {NSLog(@"视图已经加载完成");[super viewDidLoad];
    self.view.backgroundColor = [UIColor cyanColor];UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];
    label.text = @"周一见!";label.tag = 100;[self.view addSubview:label];[label release];self.view.backgroundColor = [UIColor colorWithRed:0.952 green:1.000 blue:0.456 alpha:1.000];    LoginView *loginView = [[LoginView alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    loginView.backgroundColor = [UIColor colorWithRed:0.957 green:1.000 blue:0.420 alpha:1.000];
    [self.view addSubview:loginView];
    [loginView release];

}当应用的内存快不够用时, 就会发出警告, 系统会让当前显示的视图控制器执行didReceiveMemoryWarning
- (void)didReceiveMemoryWarning {[super didReceiveMemoryWarning];// Dispose of any resources that can be recreated.NSLog(@"收到内存警告");UILabel *label = (UILabel *)[self.view viewWithTag:100];从父视图移除某个子视图
    [label removeFromSuperview];
}

#import "HomeViewController.h"
#define kSize 100
@interface HomeViewController () {UILabel *label2;UILabel *label3;UILabel *label4;
}@end
@implementation HomeViewController
- (void)viewDidLoad {[super viewDidLoad];// Do any additional setup after loading the view.self.view.backgroundColor = [UIColor colorWithRed:0.998 green:0.704 blue:1.000 alpha:1.000];UILabel *label1 = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, kSize, kSize)];label1.backgroundColor = [UIColor yellowColor];label1.text = @"1";label1.font = [UIFont systemFontOfSize:80];label1.textAlignment = NSTextAlignmentCenter;[self.view addSubview:label1];[label1 release];   label2 = [[UILabel alloc] initWithFrame:CGRectMake(375 - kSize, 0, kSize, kSize)];label2.backgroundColor = [UIColor yellowColor];label2.text = @"2";label2.font = [UIFont systemFontOfSize:80];label2.textAlignment = NSTextAlignmentCenter;[self.view addSubview:label2];[label2 release];label3 = [[UILabel alloc] initWithFrame:CGRectMake(0, 667 - kSize, kSize, kSize)];label3.backgroundColor = [UIColor yellowColor];label3.text = @"3";label3.font = [UIFont systemFontOfSize:80];label3.textAlignment = NSTextAlignmentCenter;[self.view addSubview:label3];[label3 release];label4 = [[UILabel alloc] initWithFrame:CGRectMake(375 - kSize, 667 - kSize, kSize, kSize)];label4.backgroundColor = [UIColor yellowColor];label4.backgroundColor = [UIColor yellowColor];label4.text = @"4";label4.font = [UIFont systemFontOfSize:80];label4.textAlignment = NSTextAlignmentCenter;[self.view addSubview:label4];[label4 release];
}- (void)didReceiveMemoryWarning {[super didReceiveMemoryWarning];// Dispose of any resources that can be recreated.
}UIViewController控制旋转的方法
是否支持旋转, 默认YES
- (BOOL)shouldAutorotate {return YES;
}- (NSUInteger)supportedInterfaceOrientations {        UIInterfaceOrientationMaskPortrait: 肖像模式UIInterfaceOrientationMaskLandscapeRight: 风景模式右UIInterfaceOrientationMaskPortraitUpsideDown: 肖像模式倒置UIInterfaceOrientationMaskLandscape: 风景模式(左, 右)UIInterfaceOrientationMaskAll: 四个方向UIInterfaceOrientationMaskAllButUpsideDown: 除了肖像模式倒置的所有方向iPhone项目 默认:  UIInterfaceOrientationMaskAllButUpsideDowniPad项目 默认: UIInterfaceOrientationMaskAllreturn UIInterfaceOrientationMaskAll;
}视图将要旋转, 执行这个方法
- (void)viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator {size, 当前视图的大小NSLog(@"%@", NSStringFromCGSize(size));if (size.width > size.height) {NSLog(@"横屏");view的frame不允许单独修改, 必须整体修改//1
        label2.frame = CGRectMake(667 - kSize, 0, kSize, kSize);//2
        CGRect rect = label2.frame;
        rect.origin.x = size.width - kSize;
        label2.frame = rect;} else {NSLog(@"竖屏");
       label2.frame = CGRectMake(size.width - kSize, 0, kSize, kSize);
       }CGRect rect = label2.frame;rect.origin.x = size.width - kSize;label2.frame = rect;rect = label3.frame;rect.origin.y = size.height - kSize;label3.frame = rect;rect = label4.frame;rect.origin.y = size.height - kSize;rect.origin.x = size.width - kSize;label4.frame = rect;
}

LTView.h
#import <UIKit/UIKit.h>
@interface LTView : UIView
@property (nonatomic, retain) UILabel *label;
@property (nonatomic, retain) UITextField *textField;
@end

LTView.m
#import "LTView.h"
@implementation LTView
- (void)dealloc {[_label release];[_textField release];[super dealloc];
}
- (instancetype)initWithFrame:(CGRect)frame
{self = [super initWithFrame:frame];if (self) {//label_label = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, frame.size.width / 3, frame.size.height)];
//        _label.backgroundColor = [UIColor colorWithRed:0.426 green:1.000 blue:0.956 alpha:1.000];_label.textAlignment = NSTextAlignmentCenter;[self addSubview:_label];[_label release];        //textField_textField = [[UITextField alloc] initWithFrame:CGRectMake(_label.frame.size.width, 0, frame.size.width - _label.frame.size.width, frame.size.height)];//frame.size.width / 3 * 2
//        _textField.backgroundColor = [UIColor whiteColor];
        [_textField setBorderStyle:(UITextBorderStyleRoundedRect)];[self addSubview:_textField];[_textField release];     }return self;
}
@end

LoginView.h
#import <UIKit/UIKit.h>
@class LTView;
@interface LoginView : UIView
@property (nonatomic, retain) LTView *userNameView, *passwordView;
@property (nonatomic, retain) UIButton *button;
@end

LoginView.m
#import "LoginView.h"
#import "LTView.h"
@implementation LoginView
- (void)dealloc {[_userNameView release];[_passwordView release];[_button release];[super dealloc];
}- (instancetype)initWithFrame:(CGRect)frame
{self = [super initWithFrame:frame];if (self) {//用户名self.userNameView = [[LTView alloc] initWithFrame:CGRectMake(50, 100, 275, 40)];_userNameView.label.text = @"用 户 名";_userNameView.textField.placeholder = @" 请输入用户名";[self addSubview:_userNameView];[_userNameView release];//密码self.passwordView = [[LTView alloc] initWithFrame:CGRectMake(50, 160, 275, 40)];_passwordView.label.text = @"密      码";_passwordView.textField.placeholder = @" 请输入密码";_passwordView.textField.secureTextEntry = YES;[self addSubview:_passwordView];[_passwordView release];//登录按钮self.button = [UIButton buttonWithType:UIButtonTypeSystem];_button.frame = CGRectMake(100, 220, 375 - 200, 40);
//        _button.backgroundColor = [UIColor greenColor];
//        _button.showsTouchWhenHighlighted = YES;[_button setTitle:@"登录" forState:UIControlStateNormal];_button.titleLabel.font = [UIFont systemFontOfSize:20];[self addSubview:_button];}return self;
}
@end