一些基本的类介绍

1、UIScreen可以获取设备屏幕的大小。

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// 整个屏幕的大小 {{0, 0}, {320, 480}} CGRect bounds = [UIScreen mainScreen].bounds; NSLog(@"UIScreen bounds: %@", NSStringFromCGRect(bounds));   // 应用程序窗口大小 {{0, 20}, {320, 460}} CGRect applicationFrame = [UIScreen mainScreen].applicationFrame; NSLog(@"UIScreen applicationFrame: %@", NSStringFromCGRect(applicationFrame));

2、UIView对象定义了一个屏幕上的一个矩形区域，同时处理该区域的绘制和触屏事件。
可以在这个区域内绘制图形和文字，还可以接收用户的操作。一个UIView的实例可以包含和管理若干个子UIView。

ViewController.m

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- (void)viewDidAppear:(BOOL)animated {     [super viewDidAppear:animated];     UIView* myView = [[UIView alloc] initWithFrame:CGRectMake(10, 10, 100, 100)];     myView.backgroundColor=[UIColor redColor];     [self.view addSubview:myView]; }

3、UIWindow对象是所有UIView的根，管理和协调的应用程序的显示
UIWindow类是UIView的子类，可以看作是特殊的UIView。一般应用程序只有一个UIWindow对象，即使有多个UIWindow对象，也只有一个UIWindow可以接受到用户的触屏事件。

AppDelegate.m

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- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {     UIWindow *myWindow = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];     myWindow.backgroundColor=[UIColor whiteColor];     [myWindow makeKeyAndVisible];     _window = myWindow;     returnYES; }

 4、UIViewController对象负责管理所有UIView的层次结构，并响应设备的方向变化。

AppDelegate.m

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- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {     UIWindow *myWindow = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];     myWindow.backgroundColor=[UIColor whiteColor];     UIViewController *myViewController = [[UIViewController alloc] initWithNibName:nil bundle:nil];     myWindow.rootViewController = myViewController;     [myWindow makeKeyAndVisible];     _window = myWindow;     returnYES; }

三、完整的代码

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// ViewController.h #import <UIKit/UIKit.h> @interface ViewController : UIViewController @end   // ViewController.m #import "ViewController.h" @implementation ViewController - (void)viewDidAppear:(BOOL)animated {     [super viewDidAppear:animated];     UIView* myView = [[UIView alloc] initWithFrame:CGRectMake(10, 10, 100, 50)];     myView.backgroundColor=[UIColor redColor];     [self.view addSubview:myView]; } - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {     returnYES; } @end   // AppDelegate.h #import <UIKit/UIKit.h> @classViewController; @interface AppDelegate : UIResponder <UIApplicationDelegate> @property (strong, nonatomic) UIWindow *window; @property (strong, nonatomic) ViewController *viewController; @end   // AppDelegate.m #import "AppDelegate.h" #import "ViewController.h" @implementation AppDelegate @synthesize window = _window; @synthesize viewController = _viewController; - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {     self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];     self.viewController = [[ViewController alloc] initWithNibName:nil bundle:nil];     self.window.rootViewController = self.viewController;     [self.window makeKeyAndVisible];     returnYES; } @end   // main.m #import <UIKit/UIKit.h> #import "AppDelegate.h" intmain(intargc, char*argv[]) {     @autoreleasepool {         returnUIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));     } }