How do I bind ComboBox with WPF and get SelectedItem? - wpf

Question

I am sorry I am asking question on stack over flow first time so might be some thing i done wrong.
I have started learning WPF MVVM and I'm stuck.
I have one parameter master table in a database, and it has the columns parameterid, parametername, parametertype. It is populated with master data, e.g., country master has parametertype "country", city has "city" parametertype, but parameterid will be unique.
Now I have a customer page, where in the customerviewmodel object I have countryId and CityId parameters to be saved inside the customer object.
How can I bind this parameterId directly with customer.CountryId from XAML? Or is that not possible?
Currently I have achieved it as follows: defined one CountrySelectedItem Property and bound it with combobox SelectedItem. When its property changes, when anyone changes its value then in viewmodel I set the Customer's CountryId in CountrySelectedItem set property.
How do I validate the Customer's countryID property? In the combo box, I have bound the Parameter Master's object so can't write data Annotation's Required attribute to the Parameter Master Entity.
Here are the complete Scenario
public class Customer
{
public int CustomerId { get; set; }
[Required]
public string CustomerName { get; set; }
[Required]
public int CountryId { get; set; }
}
<telerik:RadComboBox x:Name="cmCountryId" Grid.Row="3" Grid.Column="1" HorizontalAlignment="Left"
ItemsSource="{Binding LstCountry}"
HorizontalContentAlignment="Left" VerticalAlignment="Center"
DisplayMemberPath="ParameterName"
SelectedItem="{Binding SelectedCountry,Mode=TwoWay}" Height="25" Width="200" >
</telerik:RadComboBox>
/* To Fill DropDown Country DropDown From ParameterMaster*/
public List<ParameterEntity> LstCountry { get; set; }
LstContainerType = new List<ParameterEntity>(parameterService.GetParamterTypeDetail("COUNTRY").ToList());
/*
Parameter Master has ParameterId,ParameterName,ParameterType -- All Master Data Stored Inside It with Different ParameterType.
*/
/* When User Select CountrId then I Set It's ParameterID As CountryID In My CustomerEntity */
public ParameterEntity SelectedCountry
{
get
{
return _selectedCountry;
}
set
{
_selectedCountry = value;
RaisePropertyChanged("SelectedCountry");
SelectedCustomerEntity.CountryId = _selectedCountry != null ? _selectedCountry.ParameterId : 0;
}
}
So Here Is my question for above Scneraio.
1) To Bind Customer Object's CountryId Property From CountryDropDown is that any other option available then this one.
SelectedCustomerEntity.CountryId = _selectedCountry != null ? _selectedCountry.ParameterId : 0;
// please have a look SelectedCountry property.
Something like , I do not need to write Selected Property and i Can Directly Set ParameterId To CountryId Of CustomerEntity From XAML
Or this one is right scneario.
2) Another Question Is How To do Validation On CountryId ComboBox.
i mean As Mention in CustomerEntity has Required CountryId But In XAMl Design of SelectedItem="{Binding SelectedCountry,Mode=TwoWay}"
What should i write to display if user has not select any country from dropdown. Should I write a logic on Save Button manully ?

Answer 1

I'll start by making an assumption that your creating a form that will have a submit button on it that will save the selected data in some manor.
For the combobox, you can use the SelectedValuePath to select a field from the type you are binding as your selections.
<ComboBox SelectedValue="{Binding SelectedCountry}"
ItemsSource="{Binding Countries}"
SelectedValuePath="ParameterId" />
Then your SelectedCountry property in your view model will be set to the ParameterId.
For the second question of validation as well as how to bind to the Customer.CountryIdin your submit function on your model you would first check if SelectedCountry is null or empty then error out showing the validation error message. Otherwise set the Customer.CountryId = SelectedCountry and save the customer.