textFieldConstraints.swift

func textFieldConstraints() {
    // Center Text Field Relative to Page View
    NSLayoutConstraint(
      item: textField,
      attribute: .CenterX,
      relatedBy: .Equal,
      toItem: view,
      attribute: .CenterX,
      multiplier: 1.0,
      constant: 0.0)
      .active = true
    
    // Set Text Field Width to be 80% of the Width of the Page View  
    NSLayoutConstraint(
      item: textField,
      attribute: .Width,
      relatedBy: .Equal,
      toItem: view,
      attribute: .Width,
      multiplier: 0.8,
      constant: 0.0)
      .active = true
    
    // Set Text Field Y Position 10% Down From the Top of the Page View    
    NSLayoutConstraint(
      item: textField,
      attribute: .Top,
      relatedBy: .Equal,
      toItem: view,
      attribute: .Bottom,
      multiplier: 0.1,
      constant: 0.0)
      .active = true
}