Injecting services in user controls

[rbasniak]

Hi,

I tried your example, and it works great until I needed to add an user control to the project.

If I inject something in the user control, the application doesn't start. I registered the usercontrol as a singleton in the app.xaml.cs together with the MainWindow.

Do you know if this is possible?

[maythamfahmi]

I am not sure what you want to reach. As far as I know, you can not just inject UserControl as singleton, the way you do. But you have several options, one easy way is that we need to understand the life cycle of WPF and the class hierarchy, that said I might find time to come with other solutions, but for now only this one. When you start the application the first method is in MainWindow InitializeComponent() called. This method will initialize UserControl class first. so what can we do with that. Here is my suggestion:

in main windows

public readonly ILogBase LogBase;

public static MainWindow AppWindow;

public MainWindow(ILogBase logBase)
{
    AppWindow = this;
    LogBase = logBase;

    InitializeComponent();
}

And in your user control

private readonly ILogBase _logBase;

public UserControlExample()
{
    InitializeComponent();

    if(MainWindow.AppWindow?.LogBase != null)
        _logBase = MainWindow.AppWindow.LogBase;

    TestMethod();
}

I have updated the repo with this example.

[rbasniak]

Thanks for the reply. This works very well.

[pekspro]

@maythamfahmi, I suggest to instead having the ServiceProvider globally accessible. Like as a static in the App class:

 public partial class App : Application
 {
    public static IServiceProvider ServiceProvider;

Then you could use this in the user control to get the services you want:

public partial class UserControlExample: UserControl
{
    public UserControlExample()
    {
        InitializeComponent();

        DataContext = App.ServiceProvider.GetRequiredService<ILogBase>();
    }

This way the user control is not dependent on the main view.

[maythamfahmi]

@pekspro sorry for being late. I do not think it is a good idea to use static for dependency injection. If you find it solving your approach and ensure you do not get side effect. Honestly I have not tried that way.