Question

我有SelectList：

ViewData["Agency"] = new SelectList(db.Agencies.AsNoTracking().OrderBy(_ => _.AgencyID), "AgencyId", "Name");

我需要选择默认值，我试试这个：

 ViewData["Agency"] = new SelectList(db.Agencies.AsNoTracking().OrderBy(_ => _.AgencyID), "AgencyId", "Name",999);

而且：

var valueSelected = db.Agencies.AsNoTracking().Where(_=>_.AgencyId == 999).First();

ViewData["Agency"] = new SelectList(db.Agencies.AsNoTracking().OrderBy(_ => _.AgencyID), "AgencyId", "Name",valueSelected );

Answer 1

默认情况下，您需要将AgentID传递给SelectList构造函数进行设置：

 var valueSelected = db.Agencies.AsNoTracking().Where(=>.AgencyId == 999).First();

现在在SelectList中：

ViewData["Agency"] = new SelectList(db.Agencies.AsNoTracking().OrderBy(_ => _.AgencyID), "AgencyId", "Name",valueSelected.AgencyId );

Answer 2

尝试使用FirstOrDefault()代替First()。

var valueSelected = db
    .Agencies.AsNoTracking()
    .Where(_=>_.AgencyId == 999)
    .FirstOrDefault();

ViewData["Agency"] = new SelectList(db.Agencies.AsNoTracking()
    .OrderBy(_ => _.AgencyID), "AgencyId", "Name",valueSelected );

在MVC C＃中的SelectList中设置默认值

2 个答案: