CODEWITHSUNDEEP
c#wpfxamlmvvmcombobox
pgee70
pgee70

Reputation: 3974

Populating a combobox with c# using MVVM paradigm

I want to display 'user groups' in a combobox, and bind the selected usergroup key to a variable in my view model. I am using the MVVM paradigm, and I know it is very close to working but i just can't see where the issue is. usergroups is is populated dynamically after a login via a web call. I know the binding is working because if i remove the DisplayMemberPath attribute in the xaml, i see the groups.

my class UserGroup

public class UserGroup
{

    public long ugp_id;
    public String groupName;
    public float ugp_credits;
    public String logo;

    public UserGroup()
    {
    }
}

i have a xaml

 ....
 <ComboBox  Grid.Row="0" Grid.Column="2" Height="30" VerticalAlignment="Top" Margin="0,4,0,0"
        ItemsSource="{Binding userGroupCollection, Mode=OneWay}"
        DisplayMemberPath="groupName"
        SelectedValue="{Binding SelectedUgpId}"
        SelectedValuePath="ugp_id" >

in my ViewModel Class i set up an observable collection :

  public ObservableCollection<UserGroup> _userGroupCollection;
  public ObservableCollection<UserGroup> userGroupCollection
    {
        get
        {
            return _userGroupCollection;
        }
        set
        {
            if (_userGroupCollection != value)
            {
                this._userGroupCollection = value;
                DynamicOnPropertyChanged();
            }
        }
    }

after the web call this data looks as I expect it to...

but when I look at the output window when the page is viewed i see the combobox entries are blank (but the correct number are shown) and this error:

'i3SoftClient.vshost.exe' (CLR v4.0.30319: i3SoftClient.vshost.exe): Loaded 'C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\PresentationFramework-SystemCore\v4.0_4.0.0.0__b77a5c561934e089\PresentationFramework-SystemCore.dll'. Skipped loading symbols. Module is optimized and the debugger option 'Just My Code' is enabled.
System.Windows.Data Error: 40 : BindingExpression path error: 'ugp_id' property not found on 'object' ''UserGroup' (HashCode=29245900)'. BindingExpression:Path=ugp_id; DataItem='UserGroup' (HashCode=29245900); target element is 'ComboBox' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Error: 40 : BindingExpression path error: 'groupName' property not found on 'object' ''UserGroup' (HashCode=29245900)'. BindingExpression:Path=groupName; DataItem='UserGroup' (HashCode=29245900); target element is 'ComboBox' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Error: 40 : BindingExpression path error: 'ugp_id' property not found on 'object' ''UserGroup' (HashCode=29245900)'. BindingExpression:Path=ugp_id; DataItem='UserGroup' (HashCode=29245900); target element is 'ComboBox' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Error: 40 : BindingExpression path error: 'ugp_id' property not found on 'object' ''UserGroup' (HashCode=29245900)'. BindingExpression:Path=ugp_id; DataItem='UserGroup' (HashCode=29245900); target element is 'ComboBox' (Name=''); target property is 'NoTarget' (type 'Object')
System.Windows.Data Error: 40 : BindingExpression path error: 'ugp_id' property not found on 'object' ''UserGroup' (HashCode=6695955)'. BindingExpression:Path=ugp_id; DataItem='UserGroup' (HashCode=6695955); target element is 'ComboBox' (Name=''); target property is 'NoTarget' (type 'Object')

I have looked around, but I just can't seem to understand the error message.

Upvotes: 1

Views: 94

Answers (2)

hcp
hcp

Reputation: 3439

You can't use public fields for a binding. You must use properties

public class UserGroup
{

    public long ugp_id { get; set; };
    public String groupName { get; set; };
    public float ugp_credits { get; set; };
    public String logo { get; set; };

    public UserGroup()
    {
    }
}

Upvotes: 1

fahimalizain
fahimalizain

Reputation: 844

You have to do it like this :

public long ugp_id { get; set; }
public String groupName { get; set; }

Try again now :)

What the error was that those wernt properties, those were mere variables :) For Binding to work on any member, you should declare as above :)

Upvotes: 3

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