Load combobox C# from another in Load()

Question

It’s been so long since I’ve worked with Winforms, I’m missing something. In my Form Load I call this method below:

private void CarregarEstados()
{
    cboEstado.DataSource = Listas.ListaEstados();
    cboEstado.DisplayMember = "UF";
}

public static DataTable ListaEstados()
{
    DataTable _table = null;

    try
    {
        var _connector = GetSQLInstance.getInstance();
        _table = _connector.GetTable(CommandType.StoredProcedure, "SPL_CREDENCIADOS_UF_PESQUISA");
    }
    catch (Exception Error)
    {
        LastErrorCode = MazeFire.ErrorManager.GetErrorCode(Error);
        LastErrorObject = Error;
        LastError = Error.Message;
    }

    return _table;
}

The called method returns a Datatable with a column called UF. He carries the combo smoothly.

However, I was asked to automatically upload the Cities and Neighborhoods that are available in the BD. So, I do this in the event below:

private void cboEstado_SelectedIndexChanged(object sender, EventArgs e)
{
    // Assim o Combo sempre retorna vazio
    CarregarCidades(cboEstado.SelectedText);
}

private void CarregarCidades(string estado)
{
    cboCidade.DataSource = Listas.ListaCidades(estado);
    cboCidade.DisplayMember = "Cidade";
}

My problem occurs when calling the Loadings, because I can’t get the set value in the state (in the SP case). There in the example is as cboEstado.SelectedText which passes "" to the method, but I’ve tried cboEstado.SelectedValue.ToString() and cboEstado.SelectedItem.ToString() and both pass by System.Data.DataRowView as a parameter.

Could you explain to me what I’m missing?

Thank you.

Answer 1

Good morning, Daniel Afonso. I believe your problem lies in the fact that working with the event Combobox.SelectedIndexChanged(sender, e), the property ComboBox.SelectedText() always comes as an empty string. It’s right to work with ComboBox.SelectedItem().

Combobox is a component that works with a dictionary of entries that are displayed in the drop-down list, and each entry has a related object.

When we fill the Combobox with native types of value (string, int, bool, etc), the list is filled with entries 1 to 1, where the contents of the drop-down list are (objeto_referido).ToString(). Now, when filling Combobox with reference types (objects), ai has to determine which property of the object will be its entry in the drop-down list. When a particular list item is selected, the property ComboBox.SelectedItem() will return the reference to that object, not the list entry.

mas já tentei cboEstado.SelectedValue.ToString() e cboEstado.SelectedItem.ToString() e ambos passam System.Data.DataRowView

This is because you are trying to get an explicit conversion to a string of a type (Data.Datarowview) that does not have an implementation of this function. When this happens, dotnet simply returns the "full path" of the object type.

Solution in your code

There would be a million possible approximations to get around this, but I think the easiest would be to get in function call CarregarCidades(string), exchange the parameter cboEstado.SelectedText() for (cboEstado.SelectedItem).Row.Item["UF"].ToString().

Sources

https://docs.microsoft.com/pt-br/dotnet/api/system.windows.forms.combobox.selectedtext?view=netframework-4.7.2

https://docs.microsoft.com/pt-br/dotnet/api/system.data.datarowview?redirectedfrom=MSDN&view=netframework-4.7.2

https://docs.microsoft.com/pt-br/dotnet/api/system.data.datarowview.row?view=netframework-4.7.2#System_Data_DataRowView_Row