策略设计模式问题代表C＃

Question

I have trouble to use delegates and the Strategy pattern. There are two scholarships. I want to pick a random student that fulfill the scholarship criteria. It doesn't work. For the line if (pickup), it shows error "Cannot implicitly convert type 'StudentGroup.Pickup' to 'bool". How to solve it? Thank you. Is there any other error? Thanks.

public class Student
{
    public string name;
    public int year; //1 to 4
    public double gpa; //0-4.0
}

public class StudentGroup
{
    private List<Student> students = new List<Student>();
    private Random rnd = new Random();
    public delegate bool Pickup(Student x);
    public void AddStudent(string name, int year, double gpa)
    {
        Student s = new Student();
        s.name = name;
        s.year = year;
        s.gpa = gpa;
        students.Add(s);
    }

    public Student PickFor(Pickup pickup)
    {
        List<Student> candidates = new List<Student>();
        foreach (Student s in students)
        {
            if (pickup)
                candidates.Add(s);
        }

        if (candidates.Count > 0)
            return candidates[rnd.Next(candidates.Count)];
        else
            return null;
    }
}

public class Program
{
    public static void Main()
    {
        StudentGroup sg = new StudentGroup();
        sg.AddStudent("Peter", 2, 3.2);
        Student candidate1 = sg.PickFor(s => s.gpa >= 3.8);
        Student candidate2 = sg.PickFor(s => s.gpa >= 3.0 && s.year == 1);
    }
}

Answer 1

Your Pickup delegate requires an argument of type Student, so make sure to pass it one in your if statement, and also make sure you are doing something with your delegate.

if (pickup(s))
    candidates.Add(s);