Question

我如何“检查”ViewController是否具有指定var？

@objc protocol InsetBlurModalSequeProtocol {
    func getBackgroundImage() -> UIImage
}



@objc(InsetBlurModalSeque) class InsetBlurModalSeque: UIStoryboardSegue {

    override func perform() {
        var sourceViewController = self.sourceViewController as UIViewController
        let destinationViewController = self.destinationViewController as UIViewController

        // Make sure the background is ransparent
        destinationViewController.view.backgroundColor = UIColor.clearColor()

        var image:UIImage?
        if sourceViewController is InsetBlurModalSequeProtocol {
            // Use secial background plate
            image = InsetBlurModalSequeProtocol(sourceViewController).getBackgroundImage() // Error  'InsetBlurModalSequeProtocol' is not constructible with '@lvalue UIViewController'
        }
        else {
            // Take screenshot from source VC
            UIGraphicsBeginImageContext(sourceViewController.view.bounds.size)
            sourceViewController.view.drawViewHierarchyInRect(sourceViewController.view.frame, afterScreenUpdates:true)
            image = UIGraphicsGetImageFromCurrentImageContext()
            UIGraphicsEndImageContext()
        }

Answer 1

您无法检查对象是否具有某个成员变量，只有它可以转换为某种类型。一旦你知道它可以被转换为某种类型，你就可以确定它是否有一个成员变量。

你可以这样做一个可选的演员：

if let specialVc = vc as? SpecialViewController {
    // use specialVc.specialVar
}
else {
    // the view controller could not be cast so it does not have specialVar
}

如果您更喜欢使用协议，也可以使用协议。

检查UIViewController是否有某个var

1 个答案: