.NET MAUI Folder Picker: a class library implementation

Question

I'm trying to develop a .NET MAUI class library for folder picking. Following the instructions in Folder Picker .NET MAUI

• firstly, I develop an interface:

public interface IAskDirectory
{
   Task<string> AskDirectory();
}

• secondly, I created the file DirectoryAsker.cs and saved in Platform\Windows which contains

public class DirectoryAsker : IAskDirectory
{
        public async Task<string> AskDirectory()
        {
            var folderPicker = new FolderPicker();
            // Might be needed to make it work on Windows 10
            folderPicker.FileTypeFilter.Add("*");

            // Get the current window's HWND by passing in the Window object
            var hwnd = ((MauiWinUIWindow)App.Current.Windows[0].Handler.PlatformView).WindowHandle;

            // Associate the HWND with the file picker
            WinRT.Interop.InitializeWithWindow.Initialize(folderPicker, hwnd);

            var result = await folderPicker.PickSingleFolderAsync();

            return result?.Path;
        }
}

The first question is about the second step: how can I get the current Window handle? The "App" object (see line var hwnd = ...) is not recognized in a class library.

The second question is related to third step: interface registration with a generic host builder in the MauiProgram.cs. Is there a way to do this step in the class library or I have to do it every time in my main project, after having added the .dll to the references?

Answer 1

If it isn't available, then caller must provide it. A straightforward way to do so, is to pass App.Current in as a parameter to the method:

public interface IAskDirectory
{
   Task<string> AskDirectory(Application app);
}

...
public async Task<string> AskDirectory(Application app)
{
  ... app.Windows[0].Handler.PlatformView).WindowHandle;