textField: shouldChangeCharactersInRange: for decimal keyboard

gistfile1.m

-(BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
	if (textField == self.amountInput) {
		if (string.length == 0) {
			return YES; // backspace
		}

		NSNumberFormatter* numberFormatter = [[NSNumberFormatter alloc] init];
		[numberFormatter setFormatterBehavior: NSNumberFormatterBehavior10_4];
		[numberFormatter setNumberStyle: NSNumberFormatterDecimalStyle];
		
		NSString* decimalSeparator = [[[numberFormatter stringFromNumber:@0.1] substringFromIndex:1] substringToIndex:1];
		NSString* allowedCharacters = [decimalSeparator stringByAppendingString:@"0123456789"];
		
		unichar decimalSeparatorChar = [decimalSeparator characterAtIndex:0];

		NSCharacterSet *myCharSet = [NSCharacterSet characterSetWithCharactersInString:allowedCharacters];
		for (int i = 0; i < [string length]; i++) {
			unichar c = [string characterAtIndex:i];
			if (textField.text.length == 0 || [textField.text containsString:decimalSeparator]) {
				if (c == decimalSeparatorChar) {
					return NO;
				}
			}

			if (textField.text.length > 0) {
				NSString* zeros = [@"" stringByPaddingToLength:textField.text.length withString: @"0" startingAtIndex:0];
				if (c == '0' && [textField.text isEqualToString:zeros]) {
					return NO;
				}
			}
			if ([myCharSet characterIsMember:c]) {
				return YES;
			}
		}
		
		return NO;
	}
	
	return YES;
}