在WPF C＃MVVM中将现有对象绑定到组合框

Question

I am attempting to use a ComboBox to bind to a list of CostCodes . A record named SelectedRecord is passed in to be edited and I want two things to happen. Firstly, I want the ComboBox to select the CostCode that has already been applied to the SelectedRecord . I then want the user to be able to edit the CostCode so that they can assign the SelectedRecord to a different one.

I have successfully bound my ComboBox to an ObservableCollection<CostCode> , however when the user loads the Window the CostCode that is already assigned to the SelectedRecord is not selected automatically in the ComboBox . Here is the XAML:

<TextBox Grid.Row="3" Grid.Column="1" Text="{Binding SelectedRecord.Provider}"/>
<TextBox Grid.Row="4" Grid.Column="1" Text="{Binding SelectedRecord.Number}"/>
<ComboBox Grid.Row="5" Grid.Column="1" 
            ItemsSource="{Binding AllCostCodes}"
            DisplayMemberPath="Text">
</ComboBox>

I've tried using SelectedValue and SelectedValuePath but no luck. Although the user is able to edit and the CostCodes are displayed correctly when the user clicks on the ComboBox , the CostCode already assigned to the SelectedRecord is not displayed. I Included a couple of TextBoxes to show how I am binding to those, I effectively want to do exactly the same with their Text properties but with the ComboBox instead.

EDIT: CostCode.cs

public partial class CostCode
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
    public CostCode()
    {
        this.PhoneRecords = new HashSet<PhoneRecord>();
    }

    public int Id { get; set; }
    public string Text { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<PhoneRecord> PhoneRecords { get; set; }
}

PhoneRecord.cs

public partial class PhoneRecord
{
    public int Id { get; set; }
    public Nullable<System.DateTime> DateGiven { get; set; }
    public string PersonName { get; set; }
    public Nullable<int> PhoneModelId { get; set; }
    public Nullable<bool> NMU { get; set; }
    public string IMEI { get; set; }
    public string Number { get; set; }
    public Nullable<int> CostCodeId { get; set; }
    public Nullable<System.DateTime> DateReturned { get; set; }
    public string WhyReturned { get; set; }
    public string Solution { get; set; }
    public string Internet { get; set; }
    public string Provider { get; set; }
    public string SpeedDial { get; set; }
    public string OnDatabases { get; set; }
    public string Notes { get; set; }

    public virtual CostCode CostCode { get; set; }
    public virtual PhoneModel PhoneModel { get; set; }
}

SelectedRecord is chosen in a DataGrid of PhoneRecords then passed to an EditWindow where I want to set the applicable CostCode .

Answer 1

I think you need to use SelectedItem .
Something like this:

<ComboBox Grid.Row="5" Grid.Column="1" 
            ItemsSource="{Binding AllCostCodes}"
            DisplayMemberPath="Text"
            SelectedItem="{Binding SelectedRecord.CostCode}">
</ComboBox>

Edit: Just as Spongebrot and Ed Plunkett says in the comments: If it is not the same instance of the CodeCode-object then you need to override the Equals method the the CostCode object.
(In this edit I also chaned the binding from "SelectedRecord" to "SelectedRecord.CostCode" based on comments in your question.)

Edit 2: You can read about overriding Equals at MSDN .
In your case I think it should be like this:

class CostCode
{
    //... property definition of Id and Text


    public override bool Equals(System.Object obj)
    {
        // If parameter is null return false.
        if (obj as  == null)
        {
            return false;
        }

        // If parameter cannot be cast to CostCode return false.
        CostCode cc = obj as CostCode;
        if (cc == null)
        {
            return false;
        }

        // Return true if the Id fields match:
        return Id == cc.Id;
    }

    public override int GetHashCode()
    {
        return Id; // If Id is int...
    }
}