Best way to handle specifying this string?

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Hey everyone,

I'm wrecking my brain in how to best handle getting this string through a MVVM pattern, which I'm quite new at. C# also isn't my strong point so it could be a very easy solution, I have no idea. English also isn't my first langue, but I'm trying my best.

What I'm trying to do is to get a string attached to a listbox selected item via my class, without ever specifying it in a element in my xaml.

I, for example, have several labels that show the details of a selected listbox item, like so :

Content="{Binding SelectedItem.UploadDate, ElementName=LBController}"

This works amazing and I'm happy with the result.
There's also another value stored inside the connected table with a string property. This property is used for functions within my application.

Ideally I would store this string inside the application outside of an element. There's really no need to let the user see it inside a label or textbox. I'd much rather that my viewmodel immediately picks up the selected listbox value, without ever storing it inside a label or such

I already have it defined inside my viewmodel, like so.

public string CurrentXMLListboxValue { get; set; }

But how do I get the value from my listbox? I dont want to store it(CurrentXMLListboxValue) inside of a label or textbox, I want it to immediately give the value without relying on such an item. Preferably through the listbox. Is this possible following MVVM structure?

What I have tried:

I honestly have no idea if what I want to do is possible. Storing the value inside a label or textbox only to have the viewmodel read that is not my preffered method of going about it, as I do not want the value to be visible. (Neither is an invisible label or textbox, for speed reasons).

My listbox does have a binding for a selected ID, but I'm not sure if that would be of any help.

<ListBox x:Name="LBController" Grid.Column="1" HorizontalAlignment="Left" Grid.RowSpan="6" Grid.Row="1"
         ItemsSource ="{Binding AllControllers, UpdateSourceTrigger=PropertyChanged}" SelectedValue="{Binding SelectedControllerID}"
         SelectedValuePath="Id" DisplayMemberPath="Name" >
</ListBox>

Posted 19-Jun-21 10:00am

Member 15183001

Updated 21-Jun-21 3:12am

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Comments

[no name] 20-Jun-21 11:52am

With code-behind (oh horrors of horrors), you wouldn't have to "wreck your brain". And a "hidden" control is no big deal; particularly because it's the "rendering" that takes time (when doing "hundreds or thousands").

Kenneth Haugland 20-Jun-21 18:50pm

Did you implement INotifyPropertyChanged on the properties in your ViewModel? How did you link up your ViewModel to the Window?

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Richard Deeming · Answer 1 · 2021-06-21T03:12:00

Don't try to bind to the list's SelectedItem. Instead, bind to properties on your viewmodel.

C#

public IReadOnlyList<YourControllerClass> AllControllers { get; }

private int _selectedControllerId;

public int SelectedControllerId
{
    get { return _selectedControllerId; }
    set 
    { 
        if (_selectedControllerId == value) return;
        
        _selectedControllerId = value;
        OnPropertyChanged(nameof(SelectedController));
        OnPropertyChanged(nameof(UploadDate));
    }
}

public DateTime? UploadDate
{
    get
    {
        YourControllerClass selectedController = AllControllers.FirstOrDefault(c => c.Id == _selectedControllerId);
        if (selectedController == null) return null;
        return selectedController.UploadDate;
    }
}

XAML

<ListBox 
    x:Name="LBController" 
    ItemsSource="{Binding AllControllers, UpdateSourceTrigger=PropertyChanged}" 
    SelectedValue="{Binding SelectedControllerID}"
    SelectedValuePath="Id" DisplayMemberPath="Name" 
/>
<TextBlock
    Content="{Binding UploadDate}"
/>

Best way to handle specifying this string?

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Best way to handle specifying this string?

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