有效果的

/** 
 * 語(yǔ)法: #define  宏名  (變量值)
 * 編譯器是使用完全替換的語(yǔ)法來解析
 */
#define hasLaunch  (@"hasLaunch")

@interface AppDelegate ()

@end

@implementation AppDelegate


- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    
    
    //判斷是否第一次打開
    NSUserDefaults *ud = [NSUserDefaults standardUserDefaults];
    BOOL flag = [ud objectForKey:hasLaunch];
    
    
    NSLog(@"%@",flag == YES ? @"YES" : @"NO");
    
    
    if (flag == YES) {
        //不是第一次打開
        NSLog(@"%@",flag == YES ? @"YES" : @"NO" );

        //顯示首頁(yè)
        ViewController *vCtrl = [[ViewController alloc] init];
        self.window.rootViewController = vCtrl;
        
    }else{
        //第一次打開
        
        //顯示引導(dǎo)頁(yè)
        GuideViewController *guideCtrl = [[GuideViewController alloc] init];
        self.window.rootViewController = guideCtrl;
        
        [ud setBool:YES forKey:hasLaunch];
        
    }
    
    return YES;
}

?
??
?

沒效果的

#define hasLaunch  (@"hasLaunch")

@interface AppDelegate ()

@end

@implementation AppDelegate


- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    
    
    //判斷是否第一次打開
    NSUserDefaults *ud = [NSUserDefaults standardUserDefaults];
    BOOL flag = [ud objectForKey:hasLaunch];
    if (flag == YES) {
        //不是第一次打開
        
        //顯示首頁(yè)
        ViewController *vCtrl = [[ViewController alloc] init];
        self.window.rootViewController = vCtrl;
        
    }else{
        //第一次打開
        
        //顯示引導(dǎo)頁(yè)
        GuideViewController *guideCtrl = [[GuideViewController alloc] init];
        self.window.rootViewController = guideCtrl;
        
    }
    
    return YES;
}