View Injection in a WPF application

Question

As of 2015 is Prism the only choice for view injection? A lot of what i have been reading on prism has been dated by 5 years or so. Before I make the plunge into learning this framework i want to consider all my options. Is there anything comparable to Prism as far as view injection is concerned?

Answer 1

MVVM light is more... light, and easy to use. For dynamic injection, it's just a trigger on source (for load an object in modelview) and a raiseProperty on destinations controls.

                <DataGrid Grid.Column="0" Grid.Row="0" x:Name="dgMain" AutoGenerateColumns="False" SelectionUnit="FullRow" ItemsSource="{Binding Users.items}"
                CanUserReorderColumns="True" CanUserResizeColumns="True" CanUserResizeRows="False" CanUserSortColumns="True" CanUserAddRows="False"
                LoadingRow="dgMain_LoadingRow" AlternatingRowBackground="#FFEEEEEE" >
                <!--DataGrid.DataContext><Binding Source="{StaticResource tblUsers}"/></DataGrid.DataContext-->
                <i:Interaction.Triggers>
                    <i:EventTrigger EventName="SelectionChanged">
                        <mvvm:EventToCommand Command="{Binding SendUserCommand, Mode=OneWay}" CommandParameter="{Binding ElementName=dgMain, Path=SelectedItem}"></mvvm:EventToCommand>
                    </i:EventTrigger>
                </i:Interaction.Triggers>

in my case, i use a messenger

        void SendUserInfo(tblUser obj) {
        if (obj != null) {
            Messenger.Default.Send<MessageCommunicator>(new MessageCommunicator() { Emp = obj, LeMode=mode.Emp });
        }
    }
    void ReceiveInfo() {
        Messenger.Default.Register<MessageCommunicator>(this, (obj) => {
            if (obj.LeMode == mode.Emp) {
                this.UsrInfo = obj.Emp; // Stocke l'objet.
                CloneUser(); // Mémorise pour l'éventuel Undo.
            } else if (obj.LeMode == mode.Grp) { 
                this.GrpInfo = obj.Grp;
                CloneGrp();
            }
            leMode = Mode.Edit;
        });
    }

Answer 2

First of all, you don't need any framework to do view injection. prism is just one example of how it could be done. Personally, I like prism.mvvm, but I would avoid prism. It's good for learning pattern and practices, tought.

I will describe another approach called viewmodel first:

It's called viewmodel first because viewmodel is always created first and view is then selected based on naming convention or whatever logic.

Instead of injecting partial view into shell view, I inject partial viewmodel into shell viewmodel and partial view for the injected viewmodel is then created when needed.

Sample scenario:

Let's say I have main window with tabcontrol and I want to inject tabs.

In shell viewmodel I define Tabs collection (their viewmodels), that will contain injected tabs.

public class MainWindowViewModel 
{
    public MainWindowViewModel()
    {
        Tabs = new ObservableCollection<ITab>();
    }

    public ObservableCollection<ITab> Tabs { get; private set; }
}

public interface ITab
{
    string Header { get; }
}

In MainWindow.xaml I display them using converter that creates view from viewmodel

 <TabControl ItemsSource="{Binding Tabs}">
    <TabControl.ItemContainerStyle>
        <Style TargetType="TabItem">
            <Setter Property="Header" Value="{Binding Header}" />
        </Style>
    </TabControl.ItemContainerStyle>
    <TabControl.ItemTemplate>
        <DataTemplate>
            <ContentPresenter Content="{Binding Converter={StaticResource ViewModelToViewConverter}}"/>
        </DataTemplate>
    </TabControl.ItemTemplate>
</TabControl>

Example of ViewModelToViewConverter can be found here: https://stackoverflow.com/a/31721236/475727

Now the only thing you have to do is to inject tabs into Tabs collection. For example pass the collection to your modules and the module will inject the tabs.

As an alternative for injection, you can use discovery. You simply discovers all classes that implements ITab interface, instantiate them and add to the Tabs collection.

Advantages:

• You dont have to deals with strings like when using RegionManager from prism.
• You can easily test the viewmodels, including shellviewmodel
• You are not depended on any framework.