UITextfield限定只能输入数字和小数点，且不能超过8位数

适合记录支出、收入、结余的输入框

直接上代码吧，遵循UITextfield的代理，直接copy下面的代理方法就OK了

{
    BOOL isHaveDian;
}

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
    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 == '.'){
                    [[UIViewController currentViewController] showMessage:@"亲，第一个数字不能为小数点" afterDelay:1.0];
                    [textField.text stringByReplacingCharactersInRange:range withString:@""];
                    return NO;
                }
                if (single == '0') {
                    [[UIViewController currentViewController] showMessage:@"亲，第一个数字不能为0" afterDelay:1.0];
                    [textField.text stringByReplacingCharactersInRange:range withString:@""];
                    return NO;
                }
            }
            if (single=='.')
            {
                if(!isHaveDian)//text中还没有小数点
                {
                    isHaveDian=YES;
                    return YES;
                }else
                {
                    [[UIViewController currentViewController] showMessage:@"亲，您已经输入过小数点了" afterDelay:1.0];
                    [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{
                        [[UIViewController currentViewController] showMessage:@"亲，您最多输入两位小数" afterDelay:1.0];
                        return NO;
                    }
                }
                else
                {
                    if ([textField.text length] > 7) {
                        [[UIViewController currentViewController] showMessage:@"支出费用不能超过8位数" afterDelay:1.0];
                        return NO;
                    }
                    return YES;
                }
            }
        }else{//输入的数据格式不正确
            [[UIViewController currentViewController] showMessage:@"亲，您输入的格式不正确" afterDelay:1.0];
            
            [textField.text stringByReplacingCharactersInRange:range withString:@""];
            return NO;
        }
    }
    else
    {
        return YES;
    }
}