Checking to see if ViewBag has a property or not, to conditionally inject JavaScript

Question

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); } 

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.

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; } 

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

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

However, I get this error:

Cannot perform runtime binding on a null reference

Any idea?

Answer 1

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

Answer 2

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

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); }