检查 ViewBag 是否有属性，有条件地注入 JavaScript [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 Create 视图中，我想检查 ViewBag 对象，看看它是否具有 Error 属性.如果它有错误属性，我需要在页面中注入一些 JavaScript，以向我的用户显示错误消息.

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.

我创建了一个扩展方法来检查这个:

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Create视图中，我写了这行代码:

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

@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

Cannot perform runtime binding on a null reference

有什么想法吗?

推荐答案

您的代码不起作用，因为 ViewBag 是一个 动态对象 不是真实"类型.

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

以下代码应该可以工作:

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);
}

这篇关于检查 ViewBag 是否有属性，有条件地注入 JavaScript的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！