Question

I am retrieving whole data from database in list?Now i have four class like:

Student class:

public class StudentTable
{
    public string StudentID { get; set; }
    public string StudentName { get; set; }

    public StudentTable()
    {
    }

    public StudentTable(string aStudentID, string aStudentName)
    {
        StudentID = aStudentID;
        StudentName = aStudentName;
    }
}

Course class

public class CourseTable
{
    public string CourseID { get; set; }
    public string CourseName { get; set; }
    public int Credits { get; set; }

    public CourseTable()
    {
    }

    public CourseTable(string aCourseID, string aCourseName, int aCredits)
    {
        CourseID = aCourseID;
        CourseName = aCourseName;
        Credits = aCredits;
    }
}

Enrollment class

public class Enrollment
{
    public StudentTable StudentData { get; set; }
    public CourseTable CourseData { get; set; }
    public DateTime DOE { get; set; }

    public Enrollment()
    {
    }

    public Enrollment(StudentTable aStudentData, CourseTable aCourseData, DateTime aDOE)
    {
        StudentData = aStudentData;
        CourseData = aCourseData;
        DOE = aDOE;
    }
}

StudentScore class:

public class StudentScore
{

    public Enrollment EnrollmentData { get; set; }
    public int Score { get; set; }

    public StudentScore()
    {
    }

    public StudentScore(Enrollment aEnrollmentData, int aScore)
    {
        EnrollmentData = aEnrollmentData;
        Score = aScore;
    }
}

and i retrieve the data from database through query now i want to display the StudentID from list but in the StudentScore Class i have EnorllmentData not StudentID.

try
{
    var aStudentScore = EnrollmentDB.GetAllScore();
    comboBox3.DataSource = aStudentScore;

    comboBox3.DisplayMember = "StudentID";
    comboBox3.ValueMember = "CourseID";
    //comboBox3.ValueMember = "Score";
}
catch (Exception ex)
{
    MessageBox.Show(ex.Message, ex.GetType().ToString());
}

It show me a DisplayMember error can you please help me to fix it, becaouse in StudentScore class have no StudentID variable so How can i display the StudentID from StudentScore Class?

Answer 1

So, first you had the Cannot bind to new display member error which Jon solved by showing you how to use dot-notation.

After that you are now getting the Unable to cast error. Without seeing that GetAllScore method I can’t say exactly why. However, you can do the heavy lifting yourself in code, and make the binding simple, by adding read-only properties to StudentScore to return what you want to use as the Display and Value Members. (I have to say that using StudentID as a DisplayMember and CourseID as a ValueMember doesn’t make any sense to me.)

Add something like this to your StudentScore:

public String UseAsDisplayMember
{
    get 
    {
        return EnrollmentData.StudentData.StudentID; 
    }
}
public string UseAsValueMember
{
    get 
    {
        return EnrollmentData.CourseData.CourseID; 
    }
}

Then set the data binding as:

comboBox3.DisplayMember = "UseAsDisplayMember";
comboBox3.ValueMember = "UseAsValueMember";

This should get you working, but it feels more like a band-aid than a real fix.