Чистый способ - избавиться от логики в View и сохранить ее во ViewModel.
в xaml
<ComboBox ItemsSource="{Binding AgentTypes}" SelectedItem="{Binding SelectedAgentType,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}"/>
<TextBox Text="{Binding SearchText,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}" />
в ViewModel
private void SubmitAndNewCommandCallback(IEnumerable<ValidationResult> errors)
{
if (errors != null && errors.Any())
{
Errors = errors.Select(x => x.ErrorMessage).ToList();
}
else
{
if (IsNew)
{
_events.GetEvent<BidAgentCreated>().Publish(this.BidAgent);
}
SearchText="";
SelectedAgentType = AgentTypes.First(); //selects first agenttype, or set to null to select nothing in the combobox
}
}