SwiftKeyboardAvoiderHelper.swift

import UIKit

class SwiftKeyboardAvoiderHelper: NSObject, UITextFieldDelegate {
  private let durationTime: Double! = 0.2
  private var viewController: UIViewController!
  private var originalFrame: CGRect!
  private var necessaryShift: CGFloat! = 0

  var shift: CGFloat!
  var target: UIView!
  var fields: [(textField: UITextField, originalDelegate: UITextFieldDelegate?)]! = []
  
  init(viewController: UIViewController, shift: CGFloat = 10) {
    super.init()
    self.viewController = viewController
    self.shift = shift
  }
  
  // ---------------------------------------------------------------------------
  // MARK: UITextField delegates
  // ---------------------------------------------------------------------------
  func textFieldShouldReturn(textField: UITextField) -> Bool {
    if let delegate = originalDelegate(textField), textFieldShouldReturn = delegate.textFieldShouldReturn {
      textFieldShouldReturn(textField)
    }
    
    let textFields = fields.map { $0.textField }
    if let index = textFields.indexOf(textField) {
      let nextIndex = index.successor()
      if (nextIndex < textFields.count) {
        let nextField = textFields[nextIndex]
        nextField.becomeFirstResponder()
      } else {
        textField.resignFirstResponder()
      }
    }
    
    return true
  }
  
  func textFieldDidBeginEditing(textField: UITextField) {
    if let delegate = originalDelegate(textField), textFieldDidBeginEditing = delegate.textFieldDidBeginEditing {
      textFieldDidBeginEditing(textField)
    }
    self.target = textField
  }
  
  // ---------------------------------------------------------------------------
  // MARK: Keyboard observers
  // ---------------------------------------------------------------------------
  func register() {
    let textFields: [UITextField] = getTextFields(self.viewController.view)
    self.target = textFields.first
    self.fields = getDelegates(textFields)

    let keyboardDidShowSelector = #selector(KeyboardAvoider.keyboardDidShow(_:))
    let keyboardDidHideSelector = #selector(KeyboardAvoider.keyboardDidHide(_:))
    
    defaultCenter().addObserver(self, selector: keyboardDidShowSelector, name: UIKeyboardDidShowNotification, object: nil)
    defaultCenter().addObserver(self, selector: keyboardDidHideSelector, name: UIKeyboardDidHideNotification, object: nil)
  }
  
  func deregister() {
    defaultCenter().removeObserver(self)
  }
  
  @objc private func keyboardDidShow(notification: NSNotification) {
    self.returnViewToOriginalPosition()
    
    if let target = self.target {
      let info: NSDictionary! = notification.userInfo
      let keyboardDimension: CGSize! = info.objectForKey(UIKeyboardFrameBeginUserInfoKey)?.CGRectValue.size
      let screenDimension  = UIScreen.mainScreen().bounds
      let realPosition = target.convertRect(target.bounds, toView: nil)
      let endingViewFrameY = realPosition.origin.y + realPosition.size.height
      let beginingViewFrameY = screenDimension.size.height - keyboardDimension.height
      
      if endingViewFrameY + self.shift > beginingViewFrameY {
        self.necessaryShift = (endingViewFrameY - beginingViewFrameY + self.shift) * -1
      }
      
      if self.necessaryShift != 0 {
        UIView.animateWithDuration(self.durationTime, animations: {
          let frame = self.viewController.view.frame
          self.originalFrame = frame
          self.viewController.view.frame = CGRectMake(frame.origin.x, frame.origin.y + self.necessaryShift, frame.size.width, frame.size.height)
        })
      }
    }
  }
  
  @objc private func keyboardDidHide(notification: NSNotification) {
    self.returnViewToOriginalPosition()
  }
  
  // ---------------------------------------------------------------------------
  // MARK: Helpers
  // ---------------------------------------------------------------------------
  private func defaultCenter() -> NSNotificationCenter {
    return NSNotificationCenter.defaultCenter()
  }
  
  private func returnViewToOriginalPosition() {
    if self.necessaryShift != 0 {
      UIView.animateWithDuration(self.durationTime, animations: {
        let viewToAdjust: UIView! = self.viewController.view
        viewToAdjust?.frame = self.originalFrame
      })
    }
    self.necessaryShift = 0
  }
  
  private func originalDelegate(textField: UITextField) -> UITextFieldDelegate? {
    let t = fields.filter { t, d in return t == textField }
    return t.first?.originalDelegate
  }
  
  private func getTextFields(v: UIView) -> [UITextField] {
    var textFields = [UITextField]()
    
    for subview in v.subviews {
      textFields += getTextFields(subview)
      if subview is UITextField {
        textFields.append(subview as! UITextField)
      }
    }
    
    return textFields
  }
  
  private func getDelegates(textFields: [UITextField]) -> [(textField: UITextField, originalDelegate: UITextFieldDelegate?)] {
    var fields: [(textField: UITextField, originalDelegate: UITextFieldDelegate?)] = []
    for t in textFields {
      if let delegate = t.delegate {
        fields.append((textField: t, originalDelegate: delegate))
      }
      t.delegate = self
      t.returnKeyType = UIReturnKeyType.Continue
    }
    let lastTextField = textFields[textFields.count-1]
    lastTextField.returnKeyType = UIReturnKeyType.Done
    return fields
  }
}