Swift里performSelector方法的替代

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最近在回答StackOverflow的问题时，发现performSelector方法在Swift被去掉，Apple的注释是这个方法被去掉是因为不安全：

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

如果在Swift调用这个方法会编译出错：

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

方法一：

反复尝试后，我发现可以使用 UIControl：

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

下面是一段演示代码：

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() {
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调用Objective-C类的target和action，可以参考下面的例子，假设有TestClass是Objective-C类，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里可以用下面的代码执行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，好处是可以使用延迟，并且可以附带object，下面是掩饰代码：

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

另外请参考一篇不错的文章：初探swift语言的学习笔记十一(performSelector)