[摘要]本文是對Swift裡performSelector方法的替代的講解，對學習IOS蘋果軟件開發有所幫助,與大家分享。

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：

NOTE
The 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：

反復嘗試後，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 UIKit

class 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() {
        println("greetings world")
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}

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，並且有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

那麼在Swift裡可以用下面的代碼執行help方法：

import UIKit

class 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，並且可以附帶object，下面是掩飾代碼：

import UIKit

class 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!