Combobox SelectedValue not being set in binding XAML but works in C#

Question

I have a model in WPF which i am binding to a window.

pageData

holds all my data and includes one field:

pageData.orders.PrefContact

On tests on the page, this is being populated by the model (integer 1->4)

I ahve this XAML:

    <Label Content="Last Name" Grid.Column="2" Grid.Row="0" Margin="0,10,0,0" HorizontalAlignment="Right"/>
            <TextBox x:Name="txtLastName" Text="{Binding Path = order.LastName}" Grid.Column="3" Grid.Row="0" Margin="10,10,0,0" Width="200" HorizontalAlignment="Left" 
                 TabIndex="1" LostFocus="txtLastName_LostFocus" />

<Label Content="Contact Method" Grid.Column="2" Grid.Row="1" Margin="0,10,0,0" HorizontalAlignment="Right"/>
                <ComboBox x:Name="cmbPrefContact" SelectedValue="{Binding Path = order.PrefContact}" SelectionChanged="cmbPrefContact_SelectionChanged" Grid.Column="3"   
                          Width="200" Grid.Row="1" Margin="10,10,0,0" HorizontalAlignment="Left" 
                     TabIndex="3"  Height="37" VerticalAlignment="Top" />

In this case the textbox txtLastName is populated correctly, hopefully showing that the model is attached correctly to the XAML.

Within my C# I have a section to create the combobox:

private void bindCmbPref(int cmbpref)
        {
            var client = new RestClient("http://XXX.XXX.XXX:3000/comboData/contactPrefData");
            client.Timeout = -1;
            var request = new RestRequest(Method.GET);
            IRestResponse response = client.Execute(request);
            Console.WriteLine(response.Content);

            var JsonString = response.Content;
            var contactPrefData = JsonConvert.DeserializeObject<contactPrefData>(JsonString);

            foreach (var contactPrefs in contactPrefData.ContactPrefs)
            {
                
                cmbPrefContact.Items.Add(contactPrefs);
                cmbPrefContact.SelectedValuePath = "contactPrefID";
                cmbPrefContact.DisplayMemberPath = "ContactType";
            }
           
            //cmbPrefContact.SelectedValue = cmbpref;
            
        }

I have created it this way as to be honest...I don't understand the whole model/MVVM thing yet and after hours have given up on it. (for the moment). I was hoping to create the combo this way but then set the combo using the binding like my text boxes however it is not working.

If I allow the end code to work above in the c# code I can set the SelectedValue using the variable which is taken from pageData.orders.PrefContact.

What am I doing wrong here that the binding isnt working for the combobox?

EDIT: My model is below for the contactPrefs, which is a result JSON from the API I have made.

public partial class contactPrefData
    {
        public bool Result { get; set; }
        public List<contactPrefs> ContactPrefs { get; set; }

        public partial class contactPrefs
        {
            public int contactPrefID { get; set; }
            public string ContactType { get; set; }            
        }


    }

My pageData comes from this model:

public partial class OrderResponse
    {
        public bool Result { get; set; }
        public Order order { get; set; }

        public partial class Order
        {
            public long OrderId { get; set; }
            public string FirstName { get; set; }
            public string LastName { get; set; }
            public string Phone { get; set; }
            public string Email { get; set; }
            public int PrefContact { get; set; }
            public string ItemName { get; set; }
            public int ItemQuantity { get; set; }
            public string Plu { get; set; }
            public string ModelNumber { get; set; }
        }
}

C# where the order model is set to the page dataContext:

pageData = JsonConvert.DeserializeObject<OrderResponse>(JsonString);

            DataContext = pageData;

If order.PrefContact = 1:

HOWEVR if I change in DB and order.PrefContact = 2:

CURRENT WORKING SITUATION: C#:

cmbPrefContact.ItemsSource = contactPrefData.ContactPrefs;
cmbPrefContact.SelectedValuePath = "contactPrefID";
cmbPrefContact.DisplayMemberPath = "ContactType";

XAML:

<ComboBox x:Name="cmbPrefContact" 
                      
                      SelectedValue="{Binding Path = order.PrefContact}"
                      SelectedValuePath ="contactPrefID"  
                      DisplayMemberPath  ="contactType"
                      SelectionChanged="cmbPrefContact_SelectionChanged" Grid.Column="3"   
                      Width="200" Grid.Row="1" Margin="10,10,0,0" HorizontalAlignment="Left" 
                 TabIndex="3"  Height="37" VerticalAlignment="Top" />

So now I guess I'm not sure why I need to designate display member and value paths in the C# AND the XAML... but if i take one of them away on either side it stops working!

This is my contact prefs data being loaded into the combobox:

{
    "Result": true,
    "contactPrefs": [
        {
            "contactPrefID": 1,
            "ContactType": "SMS"
        },
        {
            "contactPrefID": 2,
            "ContactType": "Phone Call"
        },
        {
            "contactPrefID": 3,
            "ContactType": "Email"
        },
        {
            "contactPrefID": 4,
            "ContactType": "None"
        }
    ]
}

Final working code, worked out by mm8: XAML:

<ComboBox x:Name="cmbPrefContact" 
                      
                      SelectedValue="{Binding Path = order.PrefContact}"
                      SelectedValuePath ="contactPrefID"  
                      DisplayMemberPath  ="ContactType"
                      SelectionChanged="cmbPrefContact_SelectionChanged" Grid.Column="3"   
                      Width="200" Grid.Row="1" Margin="10,10,0,0" HorizontalAlignment="Left" 
                 TabIndex="3"  Height="37" VerticalAlignment="Top" />

C#:

var JsonString = response.Content;
            var contactPrefData = JsonConvert.DeserializeObject<contactPrefData>(JsonString);
                       
            cmbPrefContact.ItemsSource = contactPrefData.ContactPrefs;

Answer 1

You should bind the SelectedValue property to the int source property:

<ComboBox x:Name="cmbPrefContact" SelectedValue="{Binding order.PrefContact}" ... />

SelectedItem is supposed to be bound to a contactPrefs property.

You should also replace the foreach loop by setting the ItemsSource :

cmbPrefContact.ItemsSource = contactPrefData.ContactPrefs;

...and the SelectedValuePath and DisplayMemberPath in XAML:

<ComboBox x:Name="cmbPrefContact" ... SelectedValuePath = "contactPrefID" DisplayMemberPath = "ContactType" />