WPF MVVM Lights - Same user control with different parameter

Question

I have a WPF application using MVVM Light.
One MainView (+ MainViewModel) and One User Control (+ UCViewModel).

The application will have a Tab control with 2 Tab Items.
Each tab will have a user control (same user control).

User Control job: Load the contents of the file, display the contents (and allow user to export it out to other format).

When application launch, I will read a config file and will pass the file location (from config file) to each user control (Eg: File1Path, File2Path).
I can use MVVM Light Messenger.Default.Send to do this job (From MainViewModel to UCViewModel).

My issue is: How can I differentiate which User Control will get which file path?

I use SimpleIoc.Default.Register in ViewModelLocator to register my MainViewModel and UCViewModel.
At the time of registration, I do not have the data from Config file yet so I cannot pass it to UCViewModel.

Any comment/solution for my issue?

Answer 1

Method 1 (by using mm8's way)

As per @mm8 suggested, I ends up declaring DataContext for each UserControl usage in my MainViewModel class as Properties.

Example (in MainView xaml):

<v:UC Grid.Row="0" HorizontalAlignment="Stretch" Margin="10" DataContext="{Binding UC2DC}" />

However, in order for me to support my design time XAML intelliense supports, I still use default MVVM Light way of DataContext binding.

Example: In ViewModelLocator,

static ViewModelLocator()
{
    ....
    SimpleIoc.Default.Register<MainViewModel>();
    SimpleIoc.Default.Register<UCViewModel>();
    ....
}

public UCViewModel CM
{
    get
    {
        return ServiceLocator.Current.GetInstance<UCViewModel>();
    }
}

And in MainViewModel,

private UCViewModel _uC2DC;

public UCViewModel UC2DC
{
    get { return _uC2DC; }
    set { Set(ref _uC2DC, value); }
}

private UCViewModel _uC1DC;

public UCViewModel UC1DC
{
    get { return _uC1DC; }
    set { Set(ref _uC1DC, value); }
}

And somewhere in my MainViewModel, I need to create new instances and put into these properties.

When I finish everything, I will delete/comment out User Control default MVVM Light DataContext binding, ViewModelLocator's SimpleIoc Register and GetInstance property,etc and it will change to my MainView databinding.

I am not so sure does it Ok with MVVM way but as of now, it solves my issue.

Method 2 (by using Marco's way)

After Marco sample code, I came to know that we can register multiple instances of ViewModel with a key to differentiate them and when calling in property, use that key to pull the correct one.
Below is the code...

For ViewModelLocator

static ViewModelLocator()
{
    ...
    SimpleIoc.Default.Register<MainViewModel>();
    SimpleIoc.Default.Register(() => new UCViewModel(), "1");
    SimpleIoc.Default.Register(() => new UCViewModel(), "2");
    ...
}

public UCViewModel UCVM1
{
    get
    {
        return ServiceLocator.Current.GetInstance<UCViewModel>("1");
    }
}

public UCViewModel UCVM2
{
    get
    {
        return ServiceLocator.Current.GetInstance<UCViewModel>("2");
    }
}

And in my MainView XAML

<TabControl>
    <TabItem Header="Test 1">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="1*"/>
                <RowDefinition Height="70"/>
                <RowDefinition Height="70"/>
            </Grid.RowDefinitions>
            <v:UC Grid.Row="0" HorizontalAlignment="Stretch" Margin="10" 
                DataContext="{Binding UCVM1,Source={StaticResource Locator}}" />
            ...
            ...
        </Grid>
    </TabItem>
    <TabItem Header="Test 2">
        <Grid Background="AliceBlue">
            <Grid.RowDefinitions>
                <RowDefinition Height="1*"/>
                <RowDefinition Height="70"/>
                <RowDefinition Height="70"/>
            </Grid.RowDefinitions>
            <v:UC Grid.Row="0" HorizontalAlignment="Stretch" Margin="10" 
                DataContext="{Binding UCVM2,Source={StaticResource Locator}}" />
            ...
            ...
        </Grid>
    </TabItem>
</TabControl>

For this approach, it still the same, for design time, we cannot bind to one default DataContext. May be this is give and take for such cases.