Need checkbox to allow button to be pressed - IF not working

I made a button to open a date and time picker, but a CheckBox must be checked in order to activate my button. Without the checkbox, it works fine, with the chekbox checked or unchecked, it's not opening the date picker. Can you tell me why?

protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_new);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);

    pick_date = (Button) findViewById(R.id.pick_date);
    tv_result = (TextView) findViewById(R.id.tvdate_result);
    CheckBox fixed_date_flag = (CheckBox) findViewById(R.id.fixed_date);
    final boolean checked = (fixed_date_flag).isChecked();

    if(checked){
    pick_date.setOnClickListener(new View.OnClickListener()
    {
        @Override
        public void onClick(View view)
        {
            Calendar c = Calendar.getInstance();
            year = c.get(Calendar.YEAR);
            month = c.get(Calendar.MONTH);
            day = c.get(Calendar.DAY_OF_MONTH);

            DatePickerDialog datePickerDialog = new DatePickerDialog(NewActivity.this, NewActivity.this, year, month, day);
            datePickerDialog.show();
        }
    });}
}

@Override
public void onDateSet(DatePicker view, int year, int month, int dayOfMonth)
{
    yearFinal = year;
    monthFinal = month + 1;
    dayFinal = dayOfMonth;

    Calendar c = Calendar.getInstance();
    hour = c.get(Calendar.HOUR);
    minute = c.get(Calendar.MINUTE);

    TimePickerDialog timePickerDialog = new TimePickerDialog(NewActivity.this, NewActivity.this, hour, minute, DateFormat.is24HourFormat(this));
    timePickerDialog.show();

}

@Override
public void onTimeSet(TimePicker view, int hourOfDay, int minute)
{
    hourFinal = hourOfDay;
    minuteFinal = minute;
    tv_result.setText(
            "year: " + yearFinal + "\n" +
                    "month: " + monthFinal + "\n" +
                    "day: " + dayFinal +  "\n" +
                    "hour: " + hourFinal + "\n" +
                    "minute: " + minuteFinal);
}

}