iPad开发--UItextfield中输入类似于数学计算上的数字的方法

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
   
        NSCharacterSet*cs;
        
        cs = [[NSCharacterSet characterSetWithCharactersInString:NUMBERS] invertedSet];
        
        NSString*filtered = [[string componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];
        BOOL  basicTest = [string isEqualToString:filtered];
        // 只能输入数字小数点
        if(!basicTest) { // 不相等
            return NO;
        }
        
        if ([textField.text rangeOfString:@"."].location==NSNotFound) {
            isHaveDian=NO;
        }
        
        // 第一位必须为数字不能为小数点
        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=='.')
                    {
                        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:@"."];
                            int 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;
            }
        }
}