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 and a keyboard with numbers and symbols.

Is there an easy way to use the latter and prevent any non-numeric input from being entered without having to regex the final result?

Thanks!

Answer 1

Depending on the specific application, providing a slider that the user can select a position from might be a better choice on the iphone. Then no digits need to be entered at all.

Answer 2

You may want to use a slider (as suggested by Martin v. Löwis) or a UIPickerView with a separate wheel for each of the digits.

Answer 3

I wanted to do exactly the same thing, except with currencies rather than straight decimal values.

I ended up creating a custom view which contains a UITextField and a UILabel. The label covers the text field, but the text field still receives touches. I use the UITextFieldTextDidChange notification to observe changes in the text field (and I used a NSNumberFormatter to turn the resulting number into a formatted currency value) to update the label.

To disable the loupe that allows the user to reposition the insertion point, you'll need to use a custom UITextField subclass and override touchesBegan:withEvent: and set it to do nothing.

My solution might be different from what you need because the decimal point is always fixed -- I use the system's currency setting to determine how many there digits ought to be after the decimal point. However, the numeric keypad doesn't have a decimal point on it. And you can't add any buttons to the keyboard (which is especially aggravating because there's a blank button in the lower-left corner of the keyboard that would be perfect for a decimal point!) So I don't have a solution for that, unfortunately.

Answer 4

A more elegant solution happens to also be the simplest.

You don't need a decimal separator key

Why? Because you can simply infer it from the user's input. For instance, in the US locale when you what to enter in $1.23, you start by entering the numbers 1-2-3 (in that order). In the system, as each character is entered, this would be recognized as:

• user enters 1: $0.01
• user enters 2: $0.12
• user enters 3: $1.23

Notice how we inferred the decimal separator based on the user's input. Now, if the user wants to enter in $1.00, they would simply enter the numbers 1-0-0.

In order for your code to handle currencies of a different locale, you need to get the maximum fraction digits of the currency. This can be done with the following code snippet:

NSNumberFormatter *currencyFormatter = [[NSNumberFormatter alloc] init];
[currencyFormatter setNumberStyle:NSNumberFormatterCurrencyStyle];
int currencyScale = [currencyFormatter maximumFractionDigits];

For example, the Japanese yen has a maximum fraction digit of 0. So, when dealing with yen input, there is no decimal separator and thus no need to even worry about fractional amounts.

This approach to the problem allows you to use the stock numeric input keypad provided by Apple without the headaches of custom keypads, regex validation, etc.

Answer 5

For my own app I implemented shek's suggestion (by subclassing UITextField) and now I need to tell my users about the change. How do I succintly describe this style of input?

cash-register style? I'm not sure if my users are old enough to remember such antiques.

Answer 6

noob here, trying to use the formatter which i can do if i'm just formatting, but now am trying to implement this into a uitextfield to accomplish the number pressed.

does it use the text changed in the uitextfielddelegate?

maybe i'm missing something simple, but just trying to get more on that.

thanks

Answer 7

Alex, can you give more details and simple example how you did that because I am lost.

Thank you!!!

Answer 8

int currencyScale = [currencyFormatter maximumFractionDigits];

That gets me info like "USA needs 2 decimal places"... but then what do I do???

How do I change 1234 into 12.34 as the user types?

And where would I place this code?

With a dozen different keyboards on the iPhone... no one thought "oh, enter digits and decimal point" might be needed for numerical input???

And avoid the "telephone alphabet" characters altogether.

Was there a REASON why Apple didn't provide a SIMPLE "0-9 and decimal point" keyboard? (No extra code needed for any of the 10000s of "number textfields" used out there.)

Answer 9

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];
    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];
    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.

Answer 10

I built a custom Number pad view controller with decimal point... check it out:

http://sites.google.com/site/psychopupnet/iphone-sdk/tenkeypadcustom10-keypadwithdecimal