Android 如何从日期 Select 器计算年龄

我正在自学柯特林.我正在try 计算用户在输入他们的出生日期后的年龄，并将其显示在另一个活动中.

我试了很多不同的方法，但都不管用.我想我可能忽略了一些简单的东西.

我的代码是:

class MainActivity : AppCompatActivity() {
    var date1: EditText? = null
    var datePickerDialog: DatePickerDialog? = null
    lateinit var submitButton: Button
    lateinit var userInput: EditText
    lateinit var dob: EditText
    @SuppressLint("SetTextI18n", "MissingInflatedId", "CutPasteId")
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(layout.activity_main)
        date1 = findViewById<EditText>(id.date) as EditTe
        date1!!.setOnClickListener{ // calender class's instance and get current date , month and year from calender
            val c = Calendar.getInstance()
            val mYear = c[Calendar.YEAR] // current year
            val mMonth = c[Calendar.MONTH] // current month
            val mDay = c[Calendar.DAY_OF_MONTH] // current day
            datePickerDialog = DatePickerDialog(
                this@MainActivity,
                { view, year, monthOfYear, dayOfMonth -> // set day of month , month and year value in the edit text
                    date1!!.setText(
                        dayOfMonth.toString() + "/"
                                + (monthOfYear + 1) + "/" + year
                    )
                }, mYear, mMonth, mDay

            )
            datePickerDialog!!.show()

        }

        submitButton = findViewById(id.sub_btn)
        userInput = findViewById(id.username1)
        dob = findViewById(id.date)

        submitButton.setOnClickListener {
            val age= dob.text.toString()
            val name= userInput.text.toString()
            //val str = userInput.text.toString()
            intent = Intent(this, CardReturn::class.java)
            intent.putExtra("message_key","Name:$name")
            intent.putExtra("message_key1","DOB:$age")
            startActivity(intent)
        }


    }}