OC UITextField只允许输入两位小数

//只能输入两位小数
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    Boolean isHaveDian = YES;
    if ([textField.text rangeOfString:@"."].location==NSNotFound) {
        isHaveDian=NO;
    }
    if ([string length]>0)
    {
        unichar single=[string characterAtIndex:0];//当前输入的字符
        if ((single >='0' && single<='9') || single=='.')//数据格式正确
        {
            //首字母不能为0和小数点
            if([textField.text length]==0){
                if(single == '.'){
                    [textField.text stringByReplacingCharactersInRange:range withString:@""];
                    return NO;
                    
                }
                if (single == '0') {
                    
                    [textField.text stringByReplacingCharactersInRange:range withString:@""];
                    return NO;
                    
                }
            }
            if (single=='.')
            {
                if(!isHaveDian)//text中还没有小数点
                {
                    isHaveDian=YES;
                    return YES;
                }else
                {
                    [textField.text stringByReplacingCharactersInRange:range withString:@""];
                    return NO;
                }
            }
            else
            {
                if (isHaveDian)//存在小数点
                {
                    //判断小数点的位数
                    NSRange ran=[textField.text rangeOfString:@"."];
                    NSInteger tt=range.location-ran.location;
                    if (tt <= 2){
                        return YES;
                    }else{
                        return NO;
                    }
                }
                else
                {
                    return YES;
                }
            }
        }else{//输入的数据格式不正确
            
            [textField.text stringByReplacingCharactersInRange:range withString:@""];
            return NO;
        }
    }
    else
    {
        return YES;
    }
    
}