检查是否ViewBag有一个属性或没有，有条件的JavaScript注入 [英] Checking to see if ViewBag has a property or not, to conditionally inject JavaScript

问题描述

考虑这个简单的控制器：

Consider this simple controller:

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，在我的创建的看法，我想检查 ViewBag 对象，看它是否有错误财产与否。如果有错误的财产，我需要一些JavaScript注入到页面，显示错误消息，我的用户。

Now, in my Create view, I want to check ViewBag object, to see if it has Error property or not. If it has the error property, I need to inject some JavaScript into the page, to show the error message to my user.

我创建了一个扩展的方法来检查：

I created an extension method to check this:

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

然后，在创建的看法，我写了这行code的：

Then, in the Create view, I wrote this line of code:

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

不过，我得到这个错误：

However, I get this error:

无法对null引用执行运行时绑定

Cannot perform runtime binding on a null reference

任何想法？

推荐答案

您code不起作用，因为ViewBag是的 dyanmic对象不是一个'真正的'类型。

Your code doesnt work because ViewBag is a dyanmic object not a 'real' type.

以下code应该工作：

the following code should work:

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

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