iOS--输入银行卡号的时候，对数字格式化，每四个数后面加个“-”

/*
* 输入银行卡号，没四个数字后面加上“-”
*/
- (NSString *)bankCardFormat:(NSString *)string
{
NSString *result = nil;
NSString *space = @"-";
NSMutableString *mutableString = [[NSMutableString alloc] init];
[mutableString appendString:string];
int stringLength = [mutableString length];
if (stringLength >= 4) {
if (stringLength%5 == 0) {
[mutableString insertString:space atIndex:stringLength-1];
}
result = mutableString;
}else{
result = mutableString;
}
return result;
}

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
if ([string length] > 0) {
_textField.text = [self bankCardFormat:_textField.text];
}

return YES;
}