C# 如何检查输入值是否为空

我有以下Ajax Begin表单：-

@using (Ajax.BeginForm("AssignUsers", "SecurityGroup", 


    new AjaxOptions
{
    HttpMethod = "POST",
    InsertionMode = InsertionMode.Replace,
    UpdateTargetId = "UsersAssignment"//,
   // LoadingElementId = "progress",
   // OnSuccess = "reenable"
}))
{
    @Html.HiddenFor(Model => Model.GroupID)
    @Html.AntiForgeryToken()
<p>Search  <input  placeholder="Search by name.." name="selectedUserNames" type="text" data-autocomplete-source= "@Url.Action("AutoComplete", "SecurityGroup")" /> </p>

<input type="submit" value="Search" />
}

存储库方法是：-

public void AssignUserGroup(int id, string[] selectedUsers, string[] currentusernames)
        {
            var usergroups = tms.UserGroups.Where(a=>a.GroupID == id);
            foreach (var ug in usergroups)
            {
                if (currentusernames != null)
                {for (int c = 0; c < currentusernames.Count(); c++)
                    {if (ug.UserName == currentusernames[c])
                        {tms.UserGroups.Remove(ug);
                        }}}}
                if( selectedUsers !=null){
               for (int i = 0; i < selectedUsers.Count(); i++)
               {UserGroup usergroup = new UserGroup();
                   usergroup.GroupID = id;
                   usergroup.UserName = selectedUsers[i];
                   tms.UserGroups.Add(usergroup);} } }

public void AssignUserGroup（int-id，string[]selectedUsers，string[]currentusernames）
{
var usergroups=tms.usergroups.Where（a=>a.GroupID==id）；
foreach（用户组中的变量ug）
{
if（currentusernames！=null）
{for（int c=0；c

您可以执行以下操作：

 if( string.IsNullOrWhiteSpace ( your string; for example : currentusernames[c] ) ) 
 {
    -- do something or throw an exception--
 }   

 else
 {
   -- do something else --
 }

---

您需要在某个时候验证您的输入。这通常通过模型完成，然后检查

ModelState

。但是，由于生成了复杂的属性，因此最好进一步验证程序中的输入

更新存储库方法以验证提供给它的参数

public void AssignUserGroup(int id, string[] selectedUsers, string[] currentusernames)
{
    if (id < 1) throw new ArgumentExpcetion("id");
    if (selectedUsers.Length == 0) throw new ArgumentException("selectedUsers");
    if (currentusernames.Length == 0) throw new ArgumentException("currentusernames");

    var usergroups = tms.UserGroups.Where(a=>a.GroupID == id);

    // May need to user .Count instead of .Length
    if (usergroups == null || usergroups.Length == 0) throw new ArgumentOutOfRangeException("id");

    foreach (var ug in usergroups)
    {
       if (currentusernames != null)
       {
          for (int c = 0; c < currentusernames.Count(); c++)
          {
              if (ug.UserName == currentusernames[c])
              {
                  tms.UserGroups.Remove(ug);
              }
          }
       }
    }

    if( selectedUsers !=null)
    {
       for (int i = 0; i < selectedUsers.Count(); i++)
       {
           UserGroup usergroup = new UserGroup();
           usergroup.GroupID = id;
           usergroup.UserName = selectedUsers[i];
               tms.UserGroups.Add(usergroup);
       }
    }
}

public void AssignUserGroup(int id, string[] selectedUsers, string[] currentusernames)
{
    if (id < 1) throw new ArgumentExpcetion("id");
    if (selectedUsers.Length == 0) throw new ArgumentException("selectedUsers");
    if (currentusernames.Length == 0) throw new ArgumentException("currentusernames");

    var usergroups = tms.UserGroups.Where(a=>a.GroupID == id);

    // May need to user .Count instead of .Length
    if (usergroups == null || usergroups.Length == 0) throw new ArgumentOutOfRangeException("id");

    foreach (var ug in usergroups)
    {
       if (currentusernames != null)
       {
          for (int c = 0; c < currentusernames.Count(); c++)
          {
              if (ug.UserName == currentusernames[c])
              {
                  tms.UserGroups.Remove(ug);
              }
          }
       }
    }

    if( selectedUsers !=null)
    {
       for (int i = 0; i < selectedUsers.Count(); i++)
       {
           UserGroup usergroup = new UserGroup();
           usergroup.GroupID = id;
           usergroup.UserName = selectedUsers[i];
               tms.UserGroups.Add(usergroup);
       }
    }
}

try
{
   repository.AssignUserGroup(GroupID, selectedUserNames, currentUserNames);
} catch (Exception e)
{
   if (e is ArgumentException || e is ArgumentOutOfRangeException)
   {
       return redirect("Error");// Show an error view or message etc
   }

   throw; // Allow other exceptions to bubble
}