html标签从.net framework转移到.net standard(.net core 2.2)时遇到的坑及填坑

在原来的.net framework mvc中html的标签可以使用下面的方法

 1 <select class="form-control" id="categoryinfoid" name="categoryinfoid">
 2                                     "0">选择
 3                                     "22" @(categoryinfoid == 22 ? "selected=selected" : "")>内双
 4                                     "23" @(categoryinfoid == 23 ? "selected=selected" : "")>内三
 5                                     "24" @(categoryinfoid == 24 ? "selected=selected" : "")>内四
 6                                     "32" @(categoryinfoid == 32 ? "selected=selected" : "")>海双
 7                                     "33" @(categoryinfoid == 33 ? "selected=selected" : "")>海三
 8                                     "34" @(categoryinfoid == 34 ? "selected=selected" : "")>海四
 9                                     "42" @(categoryinfoid == 42 ? "selected=selected" : "")>阳双
10                                     "43" @(categoryinfoid == 43 ? "selected=selected" : "")>阳三
11                                     "44" @(categoryinfoid == 44 ? "selected=selected" : "")>阳四
12                                     "52" @(categoryinfoid == 52 ? "selected=selected" : "")>套双
13                                     "53" @(categoryinfoid == 53 ? "selected=selected" : "")>套三
14                                     "54" @(categoryinfoid == 54 ? "selected=selected" : "")>套四
15                                 select>

此时html标签里面属性与值的对应要求不是很高，但是在.net core 2.2中，html标签里面属性与值的必须要对应要求，上面得这种情况会报错

The tag helper 'option' must not have C# in the element's attribute declaration area.

标记帮助器"选项"在元素的属性声明区域中不得包含 C# 语句。

编辑器会认为，@(“...”)不是一个属性。

解决办法很奇特，看代码：

 1 <select class="form-control" id="categoryinfoid" name="categoryinfoid">
 2                                     "0">选择
 3                                     "22" @(categoryinfoid==22 ? "selected=selected" : "" )>内双
 4                                     "23" @(categoryinfoid==23 ? "selected=selected" : "" )>内三
 5                                     "24" @(categoryinfoid==24 ? "selected=selected" : "" )>内四
 6                                     "32" @(categoryinfoid==32 ? "selected=selected" : "" )>海双
 7                                     "33" @(categoryinfoid==33 ? "selected=selected" : "" )>海三
 8                                     "34" @(categoryinfoid==34 ? "selected=selected" : "" )>海四
 9                                     "42" @(categoryinfoid==42 ? "selected=selected" : "" )>阳双
10                                     "43" @(categoryinfoid==43 ? "selected=selected" : "" )>阳三
11                                     "44" @(categoryinfoid==44 ? "selected=selected" : "" )>阳四
12                                     "52" @(categoryinfoid==52 ? "selected=selected" : "" )>套双
13                                     "53" @(categoryinfoid==53 ? "selected=selected" : "" )>套三
14                                     "54" @(categoryinfoid==54 ? "selected=selected" : "" )>套四
15                                 select>

每个要使用@(“...”)的标签前面加一个“!”号就OK了，不明觉厉