Type.FindMembers() Method in C# with Examples

Type.FindMembers(MemberTypes, BindingFlags, MemberFilter, Object) Method is used to return a filtered array of MemberInfo objects of the specified member type.
Syntax:

public virtual System.Reflection.MemberInfo[] FindMembers (System.Reflection.MemberTypes memberType, System.Reflection.BindingFlags bindingAttr, System.Reflection.MemberFilter filter, object filterCriteria); 

Parameters:

• memberType: It indicates that what type of member should be searched.
• bindingAttr: It used to specify how the search is conducted or Zero, to return null.
• filter: It does the comparisons, returning true if the member currently being inspected matches the filterCriteria and false otherwise.
• filterCriteria: The search criteria that determines whether a member is returned in the array of MemberInfo objects.

The following BindingFlags filter flags can be used to define which members to include in the search:  

• You must specify either BindingFlags.Instance or BindingFlags.Static in order to get a return.
• Specify BindingFlags.Instance to include instance members in the search.
• Specify BindingFlags.Static to include static members in the search.
• Specify BindingFlags.Public to include public members in the search.
• Specify BindingFlags.NonPublic to include non-public members (that is, private, internal, and protected members) in the search.

Return Value: This method returns A filtered array of MemberInfo objects of the specified member type. or An empty array of type MemberInfo,
Exception: This method throws ArgumentNullException if filter is null.
Example:

csharp

// C# program to demonstrate the
// Type.FindMembers(MemberTypes,
// BindingFlags, MemberFilter,
// Object) Method
using System;
using System.Globalization;
using System.Reflection;

class GFG {

    // Main Method
    public static void Main()
    {
        // Declaring and initializing object of Type
        Type objType = typeof(string);

        // Creating try-catch block for handling Exception
        try {

            // Declaring and initializing the object of MemberTypes
            // that indicates the type of member to search for.
            MemberTypes mt = MemberTypes.All;

            // Declaring and initializing the object of BindingFlags
            // that specify how the search is conducted.
            BindingFlags ba = BindingFlags.Public
                          | BindingFlags.Instance;

            // Declaring and initializing MemberFilter
            // which help the delegate that compares
            // the MemberInfo against filterCriteria.
            MemberFilter mf = new MemberFilter(Search);

            // Declaring and initializing object of filterCriteria
            // the search criteria that determines whether a member is
            // returned in the array of MemberInfo objects or not
            object filterCriteria = "Equals";

            // Getting filtered array of MemberInfo by
            // using FindMembers() Method
            MemberInfo[] info = objType.FindMembers(mt, ba, mf, filterCriteria);

            // Display the Result
            for (int index = 0; index < info.Length; index++)
                Console.WriteLine("Result of FindMembers -  {0}",
                                        info[index].ToString());
        }

        // catch ArgumentNullException here
        catch (ArgumentNullException e)
        {
            Console.Write("Exception Thrown: ");
            Console.Write("{0}", e.GetType(), e.Message);
        }
    }

    // Defining MyInterfaceFilter
    // which helps to fix the certain condition
    // on which filtration took place
    public static bool Search(MemberInfo info, Object obj)
    {

        // Compare the name of the member
        // function with the filter criteria.
        if (info.Name.ToString() == obj.ToString())
            return true;
        else
            return false;
    }
}

Output:

Result of FindMembers -  Boolean Equals(System.Object)
Result of FindMembers -  Boolean Equals(System.String)
Result of FindMembers -  Boolean Equals(System.String, System.StringComparison)

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.type.findmembers?view=netcore-3.0