Thread 1:EXC_BAD_INSTRUCTION(code=EXC_I386_INVOP,subcode=0x0)

Swift语言开发中，用模拟器运行的时候总是出现![Thread 1:EXC_BAD_INSTRUCTION(code=EXC_I386_INVOP,subcode=0x0)][1]这个错误，怎么解决？求助！

源程序：
import UIKit

class ViewController: UIViewController {

@IBOutlet var wv:UIWebView

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    wv.loadRequest(NSURLRequest(URL:NSURL(string:"http://jikexueyuan.com")))
}

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

}

我出现这个错误是因为设置了代理对象，但是没签订协议，也没实现代理方法，不知道你是不是也犯了我这个低级错误