码：

UIDatePicker *datePicker = [[UIDatePicker alloc]init];
    [datePicker setDate:[NSDate date]];
    [datePicker setDatePickerMode:UIDatePickerModeDate];
    datePicker.maximumDate=[NSDate date];
    [datePicker addTarget:self action:@selector(updateBirthdateField:) forControlEvents:UIControlEventValueChanged];
    [birthdatField setInputView:datePicker];