C# Delegates as Method Parameters

Let's say you have 2 methods that go through similar steps:

public string GetPrevItem()

 {

    if (IsValidPrevEntry())

    {

        string item = GetPrevString();

        SetProperties();

         return item;

    }

   else

       return null;

 }

public string GetNextItem()

{

    if (IsValidNextEntry())

     {

        string item = GetNextString();

        SetProperties();

        return item;

     }

     else

       return null;

 }

 

These 2 methods essentially do the same thing. First, they check for some condition, and if the condition evaluates to true, they call another method, set some properties, and return a string. We can use C# delegates to refactor these 2 methods into one. Here is how you do it:
Declare 2 delegates whose signature matches the methods we want to replace:

  delegate bool IsValid();

  delegate string GetItem();

Create a method that will use the delegates:

 private string GetMyItem(IsValid isValid, GetItem getItem)

 {

   if (isValid())

   {

        string item = getItem();

         SetEventProperties();

         return item;

   }

   else

       return null;

  }       

An alternative method signature is as follows:

 private string GetNavItem(Func<bool> isValid, Func<string> getItem)

This way we don't have to declare delegates separately.

Now, we can call the new method, passing the methods that we called before refactoring, as parameters:

string strPrev =   GetMyItem(IsValidPrevEntry, GetPrevString);

string strNext =   GetMyItem(IsValidNextEntry, GetNextString);

An interesting discussion of delegates can be found on the stackflow.