`if` statement using decimal string returns false when it should be true

Question

When inspecting a text field by overriding the method below in swift:

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool

the line below returns false when I type in a 1 into the text field

var hasLeadingOne = length > 0 && decimalString.characterAtIndex(0) == (1 as unichar)

hasLeadingOne returns false but it should be true when I enter 1 into the text field. Moreover, the value of decimalString.characterAtIndex(0) seems to be 49 instead of 1 even when casted as unichar. What am I missing?

And unichar is just a typealias for UInt16. The name unichar makes it sound like it is a character of some kind, but it is just a number. — Aaron Rasmussen
– Aaron Rasmussen, Commented Dec 10, 2015 at 16:33
@Kenney More correctly, 49 is the Unicode value for the character 1. characterAtIndex: works in Unicode, not ASCII. Of course the first 127 ASCII is the same as the first 127 Unicode. — rmaddy
– rmaddy, Commented Dec 10, 2015 at 16:34
decimalString.characterAtIndex(0) == (49 as unichar) should be true, since 49 is the ASCII character code for 1, as @Kenney pointed out. — Aaron Rasmussen
– Aaron Rasmussen, Commented Dec 10, 2015 at 16:37

Aaron Rasmussen · Accepted Answer · 2015-12-10 16:52:40Z

4

A suggestion... instead of using the complex boolean test that you've constructed, Swift offers an easy way to check if a String begins with a certain sequence of characters: hasPrefix. You can simplify your code like this:

var hasLeadingOne = decimalString.hasPrefix("1")

If you want to use the boolean test that you wrote, I believe that this will work:

var hasLeadingOne = length > 0 && decimalString.characterAtIndex(0) == (49 as unichar)

edited Dec 10, 2015 at 16:52

answered Dec 10, 2015 at 16:41

Aaron Rasmussen

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