ASP.NET MVC 输出ModelState中的所有错误信息：

StringBuilder sb = new StringBuilder ();
var Keys = ModelState.Keys.ToList();
foreach (var key in Keys)
{
    var errors = ModelState[key].Errors.ToList();
    //将错误描述添加到sb中
    foreach (var error in errors)
    {
        sb.AppendLine(error.ErrorMessage);
    }

}

ViewBag.err = sb.ToString();