#import "ViewController.h"

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

#import "ViewController.h"

#define HELLO_EN @"Hello World"
#define HELLO_ZH @"你好世界"

@interface ViewController ()

@property (strong, nonatomic) UILabel *label;
@property (strong, nonatomic) UIButton *button;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    self.label = [[UILabel alloc] initWithFrame:CGRectMake(10, 50, 120, 20)];
    self.label.text = HELLO_EN;
    [self.view addSubview:self.label];
    
    self.button = [[UIButton alloc] initWithFrame:CGRectMake(10, 80, 120, 30)];
    [self.button setTitle:@"点我" forState:UIControlStateNormal];
    [self.button setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
    [self.button addTarget:self action:@selector(tapButton) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:self.button];
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)tapButton {
    self.label.text = ([self.label.text isEqualToString:HELLO_EN])?HELLO_ZH:HELLO_EN;
}

@end

#import <UIKit/UIKit.h>
#import "AppDelegate.h"

int main(int argc, char * argv[]) {
    @autoreleasepool {
        return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
    }
}

The name of the class from which the application delegate is instantiated. If principalClassName designates a subclass of UIApplication, you may designate the subclass as the delegate; the subclass instance receives the application-delegate messages. Specify nil if you load the delegate object from your application’s main nib file.

#import <UIKit/UIKit.h>

@interface AppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

@end

The UIApplicationDelegate protocol defines methods that are called by the singleton UIApplication object in response to important events in the lifetime of your app.

The app delegate works alongside the app object to ensure your app interacts properly with the system and with other apps. Specifically, the methods of the app delegate give you a chance to respond to important changes. For example, you use the methods of the app delegate to respond to state transitions, such as when your app moves from foreground to background execution, and to respond to incoming notifications. In many cases, the methods of the app delegate are the only way to receive these important notifications.

#import "AppDelegate.h"
#import "ViewController.h"
@interface AppDelegate ()

@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application willFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
//这个方法是我自己加的，默认创建的时候没有
    return YES;
}
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    self.window.rootViewController = [[ViewController alloc] init];
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application {
    // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
    // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}

- (void)applicationDidEnterBackground:(UIApplication *)application {
    // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
    // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
}

- (void)applicationWillEnterForeground:(UIApplication *)application {
    // Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
}

- (void)applicationDidBecomeActive:(UIApplication *)application {
    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}

- (void)applicationWillTerminate:(UIApplication *)application {
    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    // Saves changes in the application‘s managed object context before the application terminates.
   
}
@end

Providing a Window for Storyboarding
window
 Required Property
The window to use when presenting a storyboard.

Declaration
SWIFT
optional var window: UIWindow? { get set }
OBJECTIVE-C
@property(nonatomic, strong, nullable) UIWindow *window
Discussion
This property contains the window used to present the app’s visual content on the device’s main screen.

The UIWindow class defines an object known as a window that manages and coordinates the views an app displays on a device screen. Unless an app can display content on an external device screen, an app has only one window.

rootViewController
 Property
The root view controller for the window.

Declaration
SWIFT
var rootViewController: UIViewController?
OBJECTIVE-C
@property(nonatomic, strong, nullable) UIViewController *rootViewController
Discussion
The root view controller provides the content view of the window. Assigning a view controller to this property (either programmatically or using Interface Builder) installs the view controller’s view as the content view of the window. If the window has an existing view hierarchy, the old views are removed before the new ones are installed.