WPF Combobox databinding

babongita

I have a combobox which loads and displays exactly how I want it to, it is in a view and I am able to retrieve the pieces from this view without any problem. The problem I have is when I throw the object back at the view the combobox(which is bound to a collection of objects) the combobox doesn't show the information. What am I missing? Here is the combobox XAML:

ABitSmart

Did you try with Two-way binding ? Or else refer to this[^], Eslam has provided a sample with INotifyPropertyChanged.

User 4032528

I think that you are missing the ElementName in the ItemsSource Binding. In this case the ElementName is the x:Name of your window or UserControl. IsSynchronizedWithCurrentItem="True" TabIndex="10" Grid.Column="1" Grid.ColumnSpan="4" ItemsSource="{Binding Path=ParameterNameCollection, ElementName=UserControl, Mode=Default}" SelectedValue="{Binding SelectedParameter.Name}" Style="{DynamicResource BaseComboBox}">

ABitSmart

No, he is using DataContext of the parent implicitly.

babongita

I have tried TwoWay, but that didn't fix the problem, any other ideas?

babongita

on a side note this happens with all of the comboboxes, but I have them all coded the same so I have the same issue.

ABitSmart

Well, did you try the INotifyPropertyChanged suggestion from Eslam that I shared? Or this[^]

babongita

Yes the all of my base classes implement INotifyProperyChanged

ABitSmart

Can you share how you are updating the object in code ? Try calling the property change notification explicitly using SendPropertyChanged("ParameterNameCollection").

babongita

There are four different view models since there is are parent child relationships in this scenario. Here is an attempt to explain TabParameterViewModel has a DP of ParameterCollection (which is of Type ObservableCollection) has a DP of Parameter (bound to the selected item in a ListView) ParameterViewModel has a DP of Parameter which is set to a clone of TabParameterViewModel.Parameter has a DP of ParameterDefaultCollection (again an ObservableCollection) this.Parameter.Defaults ParameterDefaultsViewModel has a DP of ParameterDefaultCollection bound to a ListView has a DP of ParameterDefault bound to the selectedItem in the ListView ParameterDefaultViewModel has a DP of ParameterDefault which is set to a clone of ParameterDefaultsViewModel.ParameterDefault The Parameter Model has a Name property which is a class of ParameterName, which contains other attributes that are needed for the ParameterName. It also has a string property called ParameterLabel which I have bound to a textbox, when I change the SelectedItem in the listbox int TabParameterView the corresponding attributes change in the ParameterView, but any item bound to an object (in this case a Combobox) that attribute is not populated.

ABitSmart

Your orignal post had the ComboBox bound to "ParameterNameCollection" which doesn't appear in your description. What collection is it ?

babongita

The ParameterViewModel has an ObservableCollection ParameterNameCollection which is a collection of possible names that it could be, with attributes associated to that name, so the Collection is what fills the combobox, but I want the SelectedItem to be the ParameterName of the Parameter object. If I was to post the complete class for the ParameterViewModel it would look like this: ParameterViewModel has a ControlModeCollection (ObservableCollection) has a ControlTypeCollection (ObservableCollection) has a DataTypeCollection (ObservableCollection) has a ParameterMethodCollection (ObservableCollection) has a ParameterNameCollection (ObservableCollection) has a DP of SelectedParameter (of Type Parameter) has a DP of SelectedParameterDefaults (I think this is redundant since it is an ObservableCollection) Then the Parameter class looks like the following has a Name (of Type ParameterName) has a DataType (of Type DataType) has a ScreenLabel (of Type String) etc. etc. the TextBox XAML works as expected, the ComboBox doesn't

ABitSmart

babongita wrote:

but any item bound to an object (in this case a Combobox) that attribute is not populated

The above statement confuses me. It says any item bound to the object is not populated. You mean never or again just when you do something from code ?

ABitSmart

babongita wrote:

SelectedValue="{Binding SelectedParameter.Name, Mode=TwoWay}"

and

babongita wrote:

<TextBlock Text="{Binding ParameterDisplayName}"/>

I guess both of these are bound to the Parameter object. Was just curious to know if these are two different properties or a typo ? Cause your textbox is bound to a property names "ScreenLabel", which I think is the display label.

babongita wrote:

Then the Parameter class looks like the following has a Name (of Type ParameterName)

In your description, you say, Name is of type "ParameterName". So then, I suspect this,

SelectedValue="{Binding SelectedParameter.Name, Mode=TwoWay}"

Here you are binding to SelectedParameter.Name where Name is of type ParamterName. The binding will fail since it is not binding to a string type. If you open your output window in the solution explorer (assuming you are using VS) you would be able to see binding failure messages logged.

babongita

OK, There is a listbox below, which is bound to Collection of Parameters(this is a class, not what you would typically think of when you think parameters), then there is a "view" above it which shows the "detail" (attributes) of the SelectedItem in the listbox. All of the TextBoxes or the CheckBoxes show the "detail" (attributes) correctly. But when the "detail" (attribute) is an item in a Combobox the item doesn't show in the Combobox even though it is bound to that "detail"(attribute). The combobox is populated with all of the possible selections, but the SelectedItem, isn't shown in that combobox.

babongita

First of all you are correct they are bound to different properties of the Parameter object. My question is though, that I am binding the ComboBox to a Collection of Classes, and the Parameter object as a property which is a the same class, so I would think that the SelectedValue should be able to bind directly to that Value, since they are of the same type. It is just instead of it being a string object, is of another type. I tried using: SelectedValue="{Binding SelectedParameter.Name.ParameterDisplayName, Mode=TwoWay}" but then the actual property doesn't get set correctly. How can I set that combobox to be the correct item then?

ABitSmart

Give this a try,

Note: Added SelectedValuePath and changed the DataTemplate (fingers crossed ,X,, )

babongita

I have been playing with using the SelectedIndex. And it seems to work, at least for now, the problem that I foresee is that I will have to go through the Combobox source to get the index each time, in the event that the Index would change, either by addition or substraction of Metadata. What are your thoughts on that?

babongita

BTW, I tried your suggestion and the first problem was that the combobox wasn't showing what was loaded, the second problem was that the parameter.name wasn't being set either

ABitSmart

babongita wrote:

combobox wasn't showing what was loaded

What did it show then ? Was there any value in the SelectedParameter, since that is what is driving the SelectedItem.

babongita wrote:

parameter.name wasn't being set either

Why is this a combobox problem ?? Combobox is reading this value, someone has to be setting it ?? Did you check your output window? It would be logging DataBinding errors.