Question

I am new to objective c,so plz me help with this…
i have used three textfields in the interface builder
textfield1 inputs the first number
textfield2 inputs the second number

and i have created a button called sum which will calculate the sum
and textfield(ans) will display the result

.h file code

 {
      IBOutlet UITextfield txtfield1;
      IBOutlet UITextfield txtfield2;
      IBOutlet UITextfield ans;
 }
 -(IBAction)add;

.m file code

 -(IBAction)add
  {
      int result=[txtfield1.text intValue]+[txtfield2.text intValue];
      ans.text=[NSString StringWithFormat:@"%d",result];
  }

The program runs fine,but i want only integer values to be entered in the textfield,if i enter alphabets and click on the sum button i get 0 as the ans,what can i do so that user gets an error when he inputs alphabets..thanks..

Answer 1

-textField:shouldChangeCharactersInRange:replacementString: is a delegate method that let’s you allow only certain characters to be in the text field.

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string { 
    NSCharacterSet *nonNumberSet = [[NSCharacterSet decimalDigitCharacterSet] invertedSet];
    return ([string stringByTrimmingCharactersInSet:nonNumberSet].length > 0);
}

This returns YES and therefore allows only characters that are not in the decimalDigitCharacterSet character set.