［已解决］swift中makeKeyAndVisible的作用

看到别人教程中，常常出现：

makeKeyAndVisible

比如：

Swift Tutorial 1: Starting with a Single View Application -> Hello World | Swift for IOS

但是自己试了试：

加上或不加上makeKeyAndVisible：

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        // Override point for customization after application launch.
 。。。
        self.window!.makeKeyAndVisible()

        return true
    }

好像没区别。

所以要去搞清楚：

swift makeKeyAndVisible

参考：

UIWindow Class Reference

makeKeyAndVisible()
Makes the receiver the key window and visible.
Declaration
SWIFT
func makeKeyAndVisible()
Discussion
This is a convenience method to make the receiver the main window and displays it in front of other windows at the same window level or lower. You can also hide and reveal a window using the inherited hidden property of UIView.

好像就只是：

［总结］

makeKeyAndVisible的作用：

让此window作为主窗口

－》当然app一直只有一个window

－》所以此处调用或不调用makeKeyAndVisible，都不影响当前window是主窗口

注：同一时刻，只有一个主窗口

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［已解决］swift中makeKeyAndVisible的作用

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