CODEWITHSUNDEEP
c#winformscomboboxdatasource
ca9163d9
ca9163d9

Reputation: 29159

Assign a list of object which has combined keys to the DataSource of a combobox, and set DisplayMember with an expression?

I have the following code, The model class X will be filled from a database table with a composite key. The service layer method returns a list of X.

I want the drop down list shows values of A + "-" + B + "-" + C. How to set the ValueMember and DisplayMember of the combo box? Do I need to transform List<X> to a list of new class with an added property shows A + "-" + B + "-" + C? Can object reference be used as value members?

class X // A, B, C are key in the database table
{ 
    string A { get; set; } 
    string B { get; set; } 
    string C { get; set; }
    .... 
}

List<X> GetListOfX() { ..... } // from service layer

var l = GetListOfX();
ComboBox1.DataSource = l; // Or convert it to bindsource?
ComboBox1.DisplayMember = "?"; // How to display A + "-" + B + "-" + C?
ComboBox1.ValueMember = "?"; // Should it not be set so it uses the object reference?

Upvotes: 0

Views: 105

Answers (1)

Dennis
Dennis

Reputation: 37770

Do I need to transform List

Option 1. Override object.ToString method.

class X // A, B, C are key in the database table
{ 
    string A { get; set; } 
    string B { get; set; } 
    string C { get; set; }
    .... 

    public override string ToString()
    {
        return string.Format("{0}-{1}-{2}", A, B, C);
    }
}

var l = GetListOfX();
ComboBox1.DataSource = l; // that's all, you don't need to set value member or display member

Option 2. Make a sort of "view model class" (that is, transform X instances into another type).

class X_ViewModel
{ 
    public X Model { get; private set; }

    public X_ViewModel(X model)
    {
        Model = model;
    }

    string DisplayName 
    {
        get { return string.Format("{0}-{1}-{2}", A, B, C); }
    }

    .... 

}

var l = GetListOfX().Select(x => new X_ViewModel(x)).ToList();
ComboBox1.DataSource = l;
ComboBox1.DisplayMember = "DisplayName";
ComboBox1.ValueMember = "Model";

Personally, I prefer option 2, but it really depends on complexity of X, and other use-cases, applicable for X instances.

Upvotes: 1

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