检查ViewBag是否具有属性,以有条件地注入JavaScript

Question

考虑这个简单的控制器

Porduct product = new Product(){
  // Creating a product object;
};
try
{
   productManager.SaveProduct(product);
   return RedirectToAction("List");
}
catch (Exception ex)
{
   ViewBag.ErrorMessage = ex.Message;
   return View("Create", product);
}

现在,在我Create看来,我想检查ViewBag对象,看它是否有Error属性.如果它有error属性,我需要在页面中注入一些JavaScript,以向我的用户显示错误消息.

我创建了一个扩展方法来检查:

public static bool Has (this object obj, string propertyName) 
{
    Type type = obj.GetType();
    return type.GetProperty(propertyName) != null;
}

然后,在Create视图中,我写了这行代码:

@if (ViewBag.Has("Error"))
{
    // Injecting JavaScript here
}

但是,我收到此错误:

无法对空引用执行运行时绑定

任何的想法？

Answer 1

@if (ViewBag.Error!=null)
{
    // Injecting JavaScript here
}

Answer 2

您的代码不起作用,因为ViewBag是一个动态对象而不是"真实"类型.

以下代码应该工作:

public static bool Has (this object obj, string propertyName) 
{
    var dynamic = obj as DynamicObject;
    if(dynamic == null) return false;
    return dynamic.GetDynamicMemberNames().Contains(propertyName);
}