问题制作方法在应用程序启动时运行

Question

我正在开发一个将相机用于各种不同目的的应用。现在，当我启动应用程序时，我正在努力让一些代码运行：

UIImagePickerController *imageView = [[UIImagePickerController alloc]init];
imageView.delegate = self;
imageView.sourceType = UIImagePickerControllerSourceTypeCamera;
imageView.showsCameraControls = NO;

[self presentViewController:imageView animated:YES completion:NULL];

我需要在启动时对imageView UIView 对象执行此操作，因此当应用程序打开时，它会直接转到UIImagePickerController。这是我的应用程序的所有代码：

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

}

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

- (void)applicationDidBecomeActive
{

    UIImagePickerController *imageView = [[UIImagePickerController alloc]init];
    imageView.delegate = self;
    imageView.sourceType = UIImagePickerControllerSourceTypeCamera;
    imageView.showsCameraControls = NO;

    [self presentViewController:imageView animated:YES completion:NULL];


}

@end

Answer 1

如果你想在任何控制器中得到通知，你应该监听UIApplicationDidBecomeActiveNotification 或similar notifications。

- (void)viewDidLoad
{
    [super viewDidLoad];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(applicationDidBecomeActive)
                                                 name:UIApplicationDidBecomeActiveNotification 
                                               object:nil];
}

要注销，做

[[NSNotificationCenter defaultCenter] removeObserver:self 
                                                name:UIApplicationDidBecomeActiveNotification
                                              object:nil];

在dealloc 或您不想再收到通知时。

---

如果你使用故事板，你的应用代理应该是这样的

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Override point for customization after application launch.
    return YES;
}

//…

@end 

如果您不使用情节提要，您的应用委托可能是

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{    
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    [self.window makeKeyAndVisible];
    self.window.rootViewController = [[ViewController alloc] init];
    return YES;
}

//…

@end 

和你的视图控制器

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(applicationDidBecomeActive)
                                                 name:UIApplicationDidBecomeActiveNotification
                                               object:nil];
}

-(void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self
                                                    name:UIApplicationDidBecomeActiveNotification
                                                  object:nil];
}

- (void)applicationDidBecomeActive
{

    UIImagePickerController *imageViewPickerController = [[UIImagePickerController alloc] init];
    imageViewPickerController.sourceType = UIImagePickerControllerSourceTypeCamera;
    [self presentViewController:imageViewPickerController
                       animated:NO
                     completion:NULL];
}

@end

Answer 2

如果您希望在启动应用程序时运行代码，您应该将其放入：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

如果您希望 UIImagePickerController 成为第一个显示的 viewController，您应该将其设置为窗口的 rootViewController，如下所示：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // Set up imageView here

    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    [self.window makeKeyAndVisible];
    self.window.rootViewController = imageView;
    return YES;
}

如果/当您想从另一个已经在屏幕上的 viewController 呈现它时，请使用 presentViewController。