Question

我在第一个视图控制器中有函数调用（弹出视图），在应用程序中只需调用一次。从那时起，每当我返回1st View控制器时，就无需再次调用该函数。

func popView() {
        let popOverVC = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "popView") as! popView
        self.addChild(popOverVC)
        popOverVC.view.frame = self.view.frame
        self.view.addSubview(popOverVC.view)
        popOverVC.didMove(toParent: self)
    }

我在堆栈溢出中尝试了以下代码和之前的其他资源，但是没有用。.

 ///// Once Action in View Controller
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        if self.isBeingPresented || self.isMovingToParent {
         // Perform an action that will only be done once
             popView()
        }
    }

Answer 1

也许可行。在您的ViewController中，添加一个静态属性：

    static var shouldPop = true

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        if isBeingPresented || isMovingToParent {
         // Perform an action that will only be done once
             if (type(of: self).shouldPop) {
                 type(of: self).shouldPop = false
                 popView()
             }
        }
    }

当然，根据您的设置，如果您有多个此viewcontroller实例应保持自己的状态（是否应调用popView），则此方法将无效。

Answer 2

您应该在viewDidLoad方法中调用它。每个UIViewController生命周期调用一次。文档here。

就像这样：

override func viewDidLoad() {
    super.viewDidLoad()

    if self.isBeingPresented || self.isMovingToParent {
     // Perform an action that will only be done once
         popView()
    }
}

如果您曾经在视图控制器中使用过弹出视图，则可以这样做：

    /// bool that help indicate your visit 
    var isViewControllerVisited = false 

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)

        if isViewControllerVisited {
         // Perform an action that will only be done once
             popView()
        }

        //change it here
        isViewControllerVisited = true 
    }

希望有帮助！

Answer 3

根据视图控制器的生命周期，viewDidLoad方法仅被调用一次。所以您应该只在那儿调用您的方法。

或者您可以尝试以下代码：

var isScreenAppeared = false

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    if !isScreenAppeared {
         popView()
    }
    isScreenAppeared = true
}

Answer 4

在下面的代码中，尝试一下。

onUpdateNavBarColor

Answer 5

对我来说，我更喜欢使用延迟加载。这允许不编写任何逻辑，只需要使用Swift lazy var声明即可。像这样：

private lazy var viewDidAppearOnce: Bool = {
    popView()
}()

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

    _ = viewDidAppearOnce
}

Answer 6

如果您只想在您的App中调用该PopView函数一次，请尝试此操作，

在App委托中，设置bool值

int

然后，在第一个视图控制器中尝试一下，

public function submitd()
{
         $config['upload_path'] = './images';
         $config['allowed_types'] = 'gif|jpg|png|jpeg';
         $this->load->library('upload',$config);
         if($this->upload->do_upload('myfile'))
        {
           $filedata = $this->upload->data();
           $this->resize_image($filedata['full_path']);
        }
}
//you can create this function in helper or in same controller.
function resize_image($file_path) {
  $CI =& get_instance();
    // Set your config up
    $config['image_library']    = "gd2";      
    $config['source_image']     = $file_path;      
    $config['create_thumb']     = TRUE;      
    $config['maintain_ratio']   = TRUE;     
    $config['new_image'] = $file_path; 
    $config['width'] = "320";      
    $config['height'] = "240";  
    $config['thumb_marker']=FALSE;
    $CI->load->library('image_lib');

    $CI->image_lib->initialize($config);
    // Do your manipulation

    if(!$CI->image_lib->resize())
    {
       $CI->image_lib->display_errors();  
    } 
    $CI->image_lib->clear(); 

}

然后在viewdidload中这样调用，

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
     UserDefaults.standard.set(true, forKey: "showPop") // like so
     return true
}

PopView启动后在您的应用中仅出现一次，并且永远不会再次显示。

在UIViewController，iOS Swift4.2，Xcode10.1中仅调用一次函数

6 个答案: