Swift里performSelector方法的替代

2019-11-14 20:17:46

字體：大中小

來源：轉載

供稿：網友

最近在回答StackOverflow的問題時，發現performSelector方法在Swift被去掉，Apple的注釋是這個方法被去掉是因為不安全：

NOTEThe performSelector: method and related selector-invoking methods are not imported in Swift because they are inherently unsafe.

如果在Swift調用這個方法會編譯出錯：

'performSelector' is unavailable: 'performSelector' methods are unavailable

方法一：

反復嘗試后，我發現可以使用 UIControl：

func sendAction(_ action: Selector, to target: AnyObject!, forEvent event: UIEvent!)

下面是一段演示代碼：

import UIKitclass ViewController: UIViewController {                                override func viewDidLoad() {        super.viewDidLoad()        // Do any additional setup after loading the view, typically from a nib.                var control:UIControl = UIControl()        control.sendAction(Selector("greetings"), to: self, forEvent: nil)    }        func greetings() {

Log打印出：

greetings world

如果是Swift調用Objective-C類的target和action，可以參考下面的例子，假設有TestClass是Objective-C類，并且有getBarButtonItem返回UIBarButtonItem：

#import "TestClass.h"@implementation TestClass- (UIBarButtonItem *)getBarButtonItem{    UIBarButtonItem *bar = [[UIBarButtonItem alloc] init];    bar.target = self;    bar.action = @selector(help);    return bar;}- (void)help{    NSLog(@"Help offered");}@end

那么在Swift里可以用下面的代碼執行help方法：

import UIKitclass ViewController: UIViewController {                                override func viewDidLoad() {        super.viewDidLoad()        // Do any additional setup after loading the view, typically from a nib.                var testClass = TestClass()        var button: UIButton = UIButton()        var barButtonItem = testClass.getBarButtonItem()        button.sendAction(barButtonItem.action, to: barButtonItem.target, forEvent: nil)    }    }

Log打印出：

2014-07-06 23:49:49.942 TestApp [53986:2552835] Help offered

方法二：

可以使用NSThread.detachNewThreadSelector，好處是可以使用延遲，并且可以附帶object，下面是掩飾代碼：

import UIKitclass ViewController: UIViewController {        override func viewDidLoad() {        super.viewDidLoad()        // Do any additional setup after loading the view, typically from a nib.                let delay = 2.0 * Double(NSEC_PER_SEC)        var time = dispatch_time(DISPATCH_TIME_NOW, Int64(delay))        dispatch_after(time, dispatch_get_main_queue(), {            NSThread.detachNewThreadSelector(Selector("greetings:"), toTarget:self, withObject: "sunshine")        })    }        func greetings(object: AnyObject?) {        println("greetings world")        println("attached object: /(object)")    }    }

方法三：

使用NSTimer:

class func scheduledTimerWithTimeInterval(_ seconds: NSTimeInterval,                                      target target: AnyObject!,                                 selector aSelector: Selector,                                  userInfo userInfo: AnyObject!,                                    repeats repeats: Bool) -> NSTimer!

Xcode 6 Beta2

另外請參考一篇不錯的文章：初探swift語言的學習筆記十一(performSelector)