Creating Your Own "TempBag" In ASP.NET MVC

Some time back during one of my training programs I was asked this question by a beginner in ASP.NET MVC - "Can we have TempBag wrapper for TempData just as we have ViewBag for ViewData?"

Whether such a wrapper is needed or not is a different question but if you wish you can create one using dynamic objects of C# language. Here I am going to show a quick way to wrap TempData into our own TempBag and then using it in the controller and view.

The main class that does the trick is this:

public class MyTempBag : DynamicObject
{
    TempDataDictionary tempData = null;

    public MyTempBag(TempDataDictionary tempdata)
    {
        this.tempData = tempdata;
    }

    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
        try
        {
            if (tempData.Keys.Where(k => k == binder.Name).Count() > 0)
            {
                result = tempData[binder.Name];
                return true;
            }
            else
            {
                result = "Invalid TempBag Property";
                return false;
            }
        }
        catch
        {
            result = "Invalid TempBag Property";
            return false;
        }
    }

    public override bool TrySetMember(SetMemberBinder binder, object value)
    {
        try
        {
            tempData[binder.Name] = value;
            return true;
        }
        catch
        {
            return false;
        }
    }
}

The System.Dynamic namespaces provides DynamicObject class that can be used to create your own custom dynamic object. In order to create your own dynamic object using DynamicObject class you need to inherit it from DynamicObject and override three methods, viz. TryGetMember, TrySetMember and TryInvokeMember. The first two methods allow you to get and set dynamic properties whereas the last method allows you to invoke method calls on the dynamic object. In our specific case we don't need to implement TryInvokeMember because all we need is an ability to set and get properties.

The MyTempBag inherits from DynamicObject base class and accepts TempDataDictionary as its constructor parameter. The TrySetMember() method sets a TempData property value by using tempData variable. On the same lines, TryGetMember() method retrieves a TempData property value using the tempData variable.

Once you create MyTempBag class you can use it in the controller as follows:

public class HomeController : Controller
{
    dynamic TempBag = null;

    public HomeController()
    {
        TempBag = new MyTempBag(TempData);
    }

    public ActionResult Index()
    {
        TempBag.Message = "This is a test message";
        return View();
    }
}

The above code declares a dynamic variable - TempBag - inside the HomeController class. In the constructor of the HomeController this variable is set to a new instance of MyTempBag. Notice that TempData property of the controller is passed to the constructor of MyTempBag class. Once created the TempBag can be used as shown in the Index() action method.

In order to read the TempBag property inside a view you would write:

@{
    Layout = null;
    dynamic TempBag = new MyTempBag(TempData);
}

...
<html>
...
<body>
    <h3>@TempBag.Message</h3>
</body>
</html>

The view also creates an instance of MyTempBag and then reads the TempData property using TempBag object.

Creating Your Own "TempBag" In ASP.NET MVC

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