How to fix: Why is MyComboBox.Items.Count = 0, if I add as DataSource an List<MyClass> with 1 and more Elements?

Question

I need some help. I want to add an List as DataSource to a ComboBox. The List contains 1 and more elements from type "Zaehler".

I use 3 comboBoxes in my GUI. Two times it works. I create a List Element and Add Elements of T. After this I set this List as DataSource. If I check with the debugger it says that the comboBox.Items = List..Count = comboBox.DataSource.Count.

private void LadeZaehlerDaten()
{
    //NEUER ZÄHLER
    List<Zaehler> zaehlerArten = new List<Zaehler>();
    zaehlerArten.Add(new StromZaehler(1, "Stromzähler"));
    zaehlerArten.Add(new GasZaehler(2, "Gaszähler"));

    cb_ZaehlerArt.DataSource = zaehlerArten;
    cb_ZaehlerArt.DisplayMember = "Name";
    cb_ZaehlerArt.Sorted = true;
    cb_ZaehlerArt.DropDownStyle = ComboBoxStyle.DropDownList;

    Zaehler z = (Zaehler)cb_ZaehlerArt.SelectedItem;
    // ... more code

}

This code works correctly... I have zaehlerArten with 2 Elements and in the ComboBox I have 2 Items bzw. DataSource.Count = 2.

after this I create a new Zaehler and add this to List zaehlerList that will contains all correct Zaehler. This one goes wrong....

 private void LadeVertragsDaten()
 {
    //NEUER VERTRAG
    cb_VertragZaehler.DataSource = zaehlerList;
    cb_VertragZaehler.DisplayMember = "Name";       //Property in Zaehler
    cb_VertragZaehler.ValueMember = "ZaehlerNr";    //Property in Zaehler
    //cb_VertragZaehler.Sorted = true;
    cb_VertragZaehler.DropDownStyle = ComboBoxStyle.DropDownList;

    if (cb_VertragZaehler.Items.Count < 1)
    {
        return;
    }
    else
    {
        Zaehler auswahl = (Zaehler)cb_VertragZaehler.SelectedItem;
    }
 }

If I check with the debugger ... it says das cb_VertragZaehler.Items is 0 but DataSource and zaehlerList count 2.

In my opinion I didn't do anything different. It should work the same like it does with LadeZaehlerDaten()

Since the Items of the ComboBox be 0 I can't use the information of this "Zaehler".

I did say DisplayMember is Name ... even through I did hope to use something like ZaehlerNr and Name ... booth are Properties of the class Zaehler.

Could someone say why it works in LadeZaehlerDaten() but not in LadeVertragsDaten()?

Picture: DebuggerInformation

And I really do not know why..

Answer 1

The list you try to assing should be immutable. Try to create a copy of it with cb_VertragZaehler.DataSource = new List<Zaehler>(zaehlerList);