C# | Predicate Delegate

04 Apr, 2019
A Predicate delegate is an in-built generic type delegate. This delegate is defined under System namespace. It works with those methods which contain some set of criteria and determine whether the passed parameter fulfill the given criteria or not. This delegate takes only one input and returns the value in the form of true or false. Now, first of all, we see how custom delegates work in this situation. As shown in the below example.
Syntax:
public delegate bool Predicate <in P>(P obj);
Here, P is the type of the object and obj is the object which is going to compare against the criteria defined within the method represented by Predicate delegate.
Example:
// C# program to illustrate delegatesusing System;  class GFG {      // Declaring the delegate    public delegate bool my_delegate(string mystring);      // Method    public static bool myfun(string mystring)    {        if (mystring.Length < 7)         {            return true;        }          else        {            return false;        }    }      // Main method    static public void Main()    {          // Creating object of my_delegate        my_delegate obj = myfun;        Console.WriteLine(obj("Hello"));    }}
True

Now, we use the same above program with Predicate delegate as shown below.
Example: In the below example, we use a predicate delegate instead of a custom delegate. It reduces the size of the code and makes the program more readable. Here, the Predicate delegate contains a single input parameter and return output in boolean type. And here, we directly assign a myfun method to the Predicate delegate.
// C# program to illustrate Predicate delegatesusing System;  class GFG {      // Method    public static bool myfun(string mystring)    {        if (mystring.Length < 7)        {            return true;        }        else         {            return false;        }    }      // Main method    static public void Main()    {          // Using predicate delegate        // here, this delegate takes        // only one parameter        Predicate<string> val = myfun;        Console.WriteLine(val("GeeksforGeeks"));    }}
False

Important Points:
You can also use a Predicate delegate with an anonymous method as shown in the below example:Example:Predicate<string> val = delegate(string str){    if (mystring.Length < 7)    {        return true;    }    else     {        return false;    };    val("Geeks");
Example:
Predicate<string> val = delegate(string str){    if (mystring.Length < 7)    {        return true;    }    else     {        return false;    };    val("Geeks");
You can also use a Predicate delegate with the lambda expressions as shown in the below example:Example:Predicate<string> val = str = > str.Equals(str.ToLower());val("Geeks");
Example:
Predicate<string> val = str = > str.Equals(str.ToLower());val("Geeks");
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