What is the best way to enter numeric values with decimal points?

Question

In my app users need to be able to enter numeric values with decimal places. The iPhone doesn\'t provides a keyboard that\'s specific for this purpose - only a number pad an

Answer 1

Here is an example for the solution suggested in the accepted answer. This doesn't handle other currencies or anything - in my case I only needed support for dollars, no matter what the locale/currency so this was OK for me:

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range
    replacementString:(NSString *)string {

    double currentValue = [textField.text doubleValue];
    //Replace line above with this
    //double currentValue = [[textField text] substringFromIndex:1] doubleValue];
    double cents = round(currentValue * 100.0f);

    if ([string length]) {
        for (size_t i = 0; i < [string length]; i++) {
            unichar c = [string characterAtIndex:i];
            if (isnumber(c)) {
                cents *= 10;
                cents += c - '0'; 
            }            
        }
    } else {
        // back Space
        cents = floor(cents / 10);
    }

    textField.text = [NSString stringWithFormat:@"%.2f", cents / 100.0f];
    //Add this line
    //[textField setText:[NSString stringWithFormat:@"$%@",[textField text]]];
    return NO;
}

The rounds and floors are important a) because of the floating-point representation sometimes losing .00001 or whatever and b) the format string rounding up any precision we deleted in the backspace part.