所选项目未显示在WPF组合框中

Question

I'm creating a part of my window in code. For a combobox I do this:

ObservableCollection<ParamClassOption> options = new ObservableCollection<ParamClassOption>(
context.ParamClassOptions.Where(x => x.IDParamClass == val.CompTypeParam.IDParamClass));

ComboBox combobox = new ComboBox();
combobox.Name = "combobox" + val.CompTypeParam.ParameterName.Replace(" ", "");
combobox.ItemsSource = options;
combobox.SelectedValuePath = "IDParamClass";
combobox.DisplayMemberPath = "OptionName";
if (val.ParamClassOption != null)
{ 
  combobox.SelectedValue = val.ParamClassOption.IDParamClassOption; 
}
layoutitem.Content = combobox;

I'm able to select an item from the list and save it to the database. The problem that I have is to show the saved value again upon retrieving the values back from the database. Any idea why it's not showing? val.ParamClassOption.IDParamClassOption in the second to last line above has the correct value when the record is retrieved to be displayed.

Answer 1

i think you forgot to bind your selected value

var binding = new Binding {Path = new PropertyPath("IDParamClassOption"), Mode = BindingMode.TwoWay, Source = val.ParamClassOption};
combobox.SetBinding(ComboBox.SelectedValueProperty, binding);

hope this helps

Answer 2

Thanks for the help. I ended up using a completely different approach by adding the items to the combo-box one by one. I then set the selected item to previously added value (using the Text property). Here is what my code looks like now:

            if (controlType == "Combobox")
            {
                ComboBox combobox = new ComboBox();
                combobox.Name = "combobox" + val.CompTypeParam.ParameterName.Replace(" ", "");

                ObservableCollection<ParamClassOption> options = new ObservableCollection<ParamClassOption>(
                    context.ParamClassOptions.Where(x => x.IDParamClass == val.CompTypeParam.IDParamClass));
                combobox.Items.Clear(); 
                foreach (ParamClassOption option in options)
                {
                    ComboBoxItem item = new ComboBoxItem();
                    item.Content = option.OptionName;
                    combobox.Items.Add(item);
                }
                combobox.Text = val.ParamClassOption.OptionName;

                layoutitem.Content = combobox;
            }

Later when reading the value from the combobox to save to the database I did this:

ObservableCollection<ParamClassOption> option = new ObservableCollection<ParamClassOption>(
    context.ParamClassOptions.Where(o => o.IDParamClass == value.CompTypeParam.IDParamClass).Where(o => o.OptionName == combobox.Text));
value.IDParamClassOption = option[0].IDParamClassOption;