键盘出现约束时快速向上移动

Question

I am using the following code from "Programming iOS 8". I have a subview with constraints that contains a simple textfield. This view has top and bottom to superview constraints, which I have outlets for. I have an outlet for the subview as well. The goal here is that when the keyboard appears, it pushes this subview up. I get an error on the line "let f = self.fr!.frame" Thread 1: EXC_BAD_INSTRUCTION. Does it have to do with needing to unwrap the optional? Could it be an issue with my constraints? Any help would be much appreciated. Thanks.

import UIKit

class ViewController: UIViewController {

@IBOutlet var topSpace: NSLayoutConstraint!
@IBOutlet var bottomSpace: NSLayoutConstraint!
@IBOutlet var slidingView: UIView!
var fr: UIView?

override func viewDidLoad() {
    NSNotificationCenter.defaultCenter().addObserver(
        self, selector: "keyboardShow:",
        name: UIKeyboardWillShowNotification, object: nil)
    NSNotificationCenter.defaultCenter().addObserver(
        self, selector: "keyboardHide:",
        name: UIKeyboardWillHideNotification, object: nil)




    super.viewDidLoad()   

}


func textFieldDidBeginEditing(tf: UITextField) {
    self.fr = tf // keep track of the first responder
}

func textFieldShouldReturn(tf: UITextField) -> Bool {

    tf.resignFirstResponder()
    self.fr = nil
    return true

}

func keyboardShow(n:NSNotification) {
    let d = n.userInfo!
    var r = (d[UIKeyboardFrameEndUserInfoKey] as NSValue).CGRectValue()
    r = self.slidingView.convertRect(r, fromView:nil)
    let f = self.fr!.frame
    let y : CGFloat =
    f.maxY + r.size.height - self.slidingView.bounds.height + 5
    if r.origin.y < f.maxY {
        self.topSpace.constant = -y
        self.bottomSpace.constant = y
        self.view.layoutIfNeeded()
    }
}

func keyboardHide(n:NSNotification){
    self.topSpace.constant = 0
    self.bottomSpace.constant = 0
    self.view.layoutIfNeeded()
}



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


}

Answer 1

If I'm not mistaken, the keyboard shows before you start editing, so your self.fr is still nil when your keyboard is shown. Check to see if it's nil. It shouldn't have to do anything with the optional unwrapping. It only fails when you unwrap a null.