根据textfield的内容显示不同button的图像
import UIKit
class ViewController：UIViewController,UITextFieldDelegate {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view,typically from a nib.
let rect = CGRect(x：10, y：80, width：300, height：40)
let textField = UITextField(frame：rect)
textField.placeholder = “Bank card no”
textField.autocorrectionType =UITextAutocorrectionType.no
textField.returnKeyType = UIReturnKeyType.done
textField.clearButtonMode =UITextFieldViewMode.whileEditing
textField.keyboardType = UIKeyboardType.numberPad
textField.keyboardAppearance =UIKeyboardAppearance.dark
textField.delegate = self
textField.borderStyle = UITextBorderStyle.line
// textField.clearButtonMode = .whileEditing
let btnLeft：UIButton = UIButton(type：UIButtonType.custom)
btnLeft.frame = CGRect(x：0,y：0,width：30,height：30)
btnLeft.setBackgroundImage(UIImage(named：”银行信息”), for：UIControlState())
textField.leftView = btnLeft
textField.leftViewMode = .unlessEditing
let btnRight：UIButton = UIButton(type：UIButtonType.custom)
btnRight.frame = CGRect(x：0,y：0,width：30,height：30)
textField.rightViewMode = .always
btnRight.addTarget(self, action：#selector(touchupInsideBtnAction(：)), for：
UIControlEvents.touchUpInside)
btnRight.setBackgroundImage(UIImage(named：”相机”), for：UIControlState())
textField.rightView = btnRight
self.view.addSubview(textField)
}
func textFieldShouldReturn( textField：UITextField)-> Bool {
textField.resignFirstResponder()
return true
}
func touchupInsideBtnAction(_ btn：UIButton)
{
let message = “模拟拍照扫描银行卡.”
let alert = UIAlertController(title：“Information”,message：message, preferredStyle：UIAlertControllerStyle.alert)
let OKAction = UIAlertAction(title：“OK”, style：UIAlertActionStyle.default, handler：nil)
alert.addAction(OKAction)
self.present(alert, animated：true, completion：nil)
}
}