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Swift里performSelector方法的替代

关键词:SwiftperformSelector  阅读(3559) 赞(16)

[摘要]本文是对Swift里performSelector方法的替代的讲解,对学习IOS苹果软件开发有所帮助,与大家分享。

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 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 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,好处是可以使用延迟,并且可以附带object,下面是掩饰代码:

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!


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