Add a button on right view of UItextfield in such way that, text should not overlap the button

use the rightView property of the UITextField. Basically, there are two properties (this one and leftView accordingly) that allow you to place custom views/controls inside the UITextField. You can control whether those views are shown or not by means of rightViewMode/leftViewMode properties:

textField.rightView = btnColor
textField.rightViewMode = .unlessEditing

for e.g

let button = UIButton(type: .custom)
button.setImage(UIImage(named: "send.png"), for: .normal)
button.imageEdgeInsets = UIEdgeInsetsMake(0, -16, 0, 0)
button.frame = CGRect(x: CGFloat(txt.frame.size.width - 25), y: CGFloat(5), width: CGFloat(25), height: CGFloat(25))
button.addTarget(self, action: #selector(self.refresh), for: .touchUpInside)
textField.rightView = button
textField.rightViewMode = .always

and call the action as

@IBAction func refresh(_ sender: Any) {
}

Create UITextField extension and add below method in it and you can change UIButton code as per your requirement.

func setRightViewIcon(icon: UIImage) {
    let btnView = UIButton(frame: CGRect(x: 0, y: 0, width: ((self.frame.height) * 0.70), height: ((self.frame.height) * 0.70)))
    btnView.setImage(icon, for: .normal)
    btnView.imageEdgeInsets = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 3)
    self.rightViewMode = .always
    self.rightView = btnView
}

Correct answer Swift3+

If you just override the methods, the text may overlap the right view. This code completely solves this problem.

You UITextField subclass:

//...

private func setInsets(forBounds bounds: CGRect) -> CGRect {

    var totalInsets = insets //property in you subClass

    if let leftView = leftView  { totalInsets.left += leftView.frame.origin.x }
    if let rightView = rightView { totalInsets.right += rightView.bounds.size.width }

    return UIEdgeInsetsInsetRect(bounds, totalInsets)
}

override func textRect(forBounds bounds: CGRect) -> CGRect {
    return setInsets(forBounds: bounds)
}

override func placeholderRect(forBounds bounds: CGRect) -> CGRect {
    return setInsets(forBounds: bounds)
}

override func editingRect(forBounds bounds: CGRect) -> CGRect {
    return setInsets(forBounds: bounds)
}

override func rightViewRect(forBounds bounds: CGRect) -> CGRect {

    var rect = super.rightViewRect(forBounds: bounds)
    rect.origin.x -= insets.right

    return rect
}

override func leftViewRect(forBounds bounds: CGRect) -> CGRect {

    var rect = super.leftViewRect(forBounds: bounds)
    rect.origin.x += insets.left

    return rect
}