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Strongly Typing TempData in your MVC Application with Extension Methods

As I’ve stated before, and for those that know me, when working with C# I try to use the compiler as often as I can and keep things strongly typed.  When I started working in MVC, I didn’t like the fact that TempData was defined like this:

  public class TempDataDictionary : IDictionary<string, object>, ICollection<KeyValuePair<string, object>>, IEnumerable<KeyValuePair<string, object>>, IEnumerable

While TempData and ViewData being potentially valuable things, <string, object>, really?

Here is how I get around that and use the compiler to my advantage with some simple extension methods:

public static class TempDataExtensions
{
    public static T Get<T>(this TempDataDictionary tempData, string key)
    {
        if (tempData[key] is T)
        {
            var tempDataItem = (T)tempData[key];
            return tempDataItem;
        }
        throw new InvalidCastException(string.Format("Temp Data does not contain type {0} for key {1}", typeof(T), key));
    }

    public static void Set<T>(this TempDataDictionary tempData, string key, T value)
    {
        tempData[key] = value;
    }
}

So, in your controller, you can Set to TempData and Get from TempData like this:

public ActionResult Index()
{
    TempData.Set("SomeObjectKey", new SomeObject());
    TempData.Set("SomeBoolKey", true);
    TempData.Set("SomeStringKey", "test");
    
    TempData.Get<SomeObject>("SomeObjectKey"); // returns SomeObject
    TempData.Get<bool>("SomeBoolKey"); // returns a boolean true
    TempData.Get<string>("SomeStringKey"); // returns the string "test"

    return View();
}

You can also do the same with ViewData:

public static class ViewDataExtensions
{
    public static T Get<T>(this ViewDataDictionary viewData, string key)
    {
        if (viewData[key] is T)
        {
            var viewDataItem = (T)viewData[key];
            return viewDataItem;
        }
        throw new InvalidCastException(string.Format("View Data does not contain type {0} for key {1}", typeof(T), key));
    }

    public static void Set<T>(this ViewDataDictionary viewData, string key, T value)
    {
        viewData[key] = value;
    }
}

 

I know what you are thinking, this doesn’t stop you from setting TempData the <string, object> way, and you are correct.  To get and set using strong types, you have to have the discipline to use these extension methods.  But, with these you can give yourself a fighting chance.

Don’t litter your code with stringly typed settings, mkay?

h9cnk

When using C#, I am kinda a strongly typed bigot and like to use the compiler as much as I can. Since practically every application I have ever worked on has had some sort of setting access from a config file, I felt that there had to be a better way.

So, given this config file:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="StringSetting" value="filepath"/>
    <add key="BoolSetting" value="true"/>
    <add key="StringListDelimitedSetting" value="one;two;three"/>
  </appSettings>
</configuration>

 

I don’t want to litter my code with this everywhere:

//BAD
string value = System.Configuration.ConfigurationManager.AppSettings["StringSetting"];
if (value == "SOMETHING")
{
    //do something
}
 
//WORSE?
string boolValue = System.Configuration.ConfigurationManager.AppSettings["BoolSetting"];
if (boolValue == "YES")
{
    //do something
}
 
//PRODUCES STRONG TYPE BUT EVEN MORE CODE
string someOtherBoolValue = System.Configuration.ConfigurationManager.AppSettings["SomeOtherBoolSetting"];
bool strongBoolValue;
if (Boolean.TryParse(someOtherBoolValue, out strongBoolValue))
{
    if (strongBoolValue)
    {
        //do something
    }
}

 

So, this is what I do to keep my “stringly” typed settings in one place, strongly typed and make them easily accessible in my code:

public static class AppSettingsExtensions
{
    public static string StringSetting(this NameValueCollection settings)
    {
        string setting = settings["StringSetting"];
        if (setting != null && !string.IsNullOrWhiteSpace(setting))
        {
            return setting;
        }
 
        return string.Empty;
    }
 
    public static bool BoolSetting(this NameValueCollection settings)
    {
        string setting = settings["BoolSetting"];
        if (setting != null && !string.IsNullOrWhiteSpace(setting))
        {
            bool test;
            if (Boolean.TryParse(setting, out test))
            {
                return test;
            }
        }
 
        return false;
    }
 
    public static IEnumerable<string> StringListDelimitedSetting(this NameValueCollection settings)
    {
        string setting = settings["StringListDelimitedSetting"];
        if (setting != null && !string.IsNullOrWhiteSpace(setting))
        {
            return setting.Split(Convert.ToChar(";"), Convert.ToChar(",")).ToList();
        }
 
        return Enumerable.Empty<string>();
    }
}

 

Accessing settings in code now is simple and gives you a strong type:

//GOOD
string stringSetting = ConfigurationManager.AppSettings.StringSetting();
if (stringSetting == "SOMETHING")
{
    //do something
}

//OR
bool boolSetting = ConfigurationManager.AppSettings.BoolSetting();
if (boolSetting)
{
    //do something
}

//OR
IEnumerable<string> listSettings = ConfigurationManager.AppSettings.StringListDelimitedSetting();
foreach (string setting in listSettings)
{
    //do something
}

 

And yes, this works for connections strings as well, just change the type of the extension:

public static class ConnectionStringExtensions
{
    public static string SomeConnectionString(this ConnectionStringSettingsCollection settings)
    {
        ConnectionStringSettings setting = settings["SomeConnectionString"];
        if (setting != null)
        {
            string connectionString = setting.ConnectionString;
            if (!string.IsNullOrWhiteSpace(connectionString))
            {
                return connectionString;
            }
        }

        return string.Empty;
    }
}

 

Accessed like:

string connectionString = ConfigurationManager.ConnectionStrings.SomeConnectionString();

 

And there you have it, that is a tool I like to keep in my toolbox when working with configuration files.