I'm new to .Net Maui but have completed James Montemagno's 4 hour Workshop. Included in the Workshop was:

1. Creating a Page with a CollectionView
2. Creating a ViewModel
3. Creating an async method which calls a data service to retrieve data
4. Configuring the async method as a ICommand
5. Binding the data model list to the CollectionView
6. Binding the Command to a Button

Clicking the button works and populates the CollectionView. How would I go about removing the button and performing this action when the page opens? Note I tried modifying the method by removing the "[ICommand]" which did not work. Also, should this action be done in the Code Behind or in the ViewModel?

Thanks in advance for assistance!

(ModelView)

public partial class FieldAssignedWbsViewModel : BaseViewModel

{
FieldAssignedWbsService fieldAssignedWbsService;
public ObservableCollection<FieldAssignedWbs> WbsList { get; set; } = new();

public FieldAssignedWbsViewModel(FieldAssignedWbsService fieldAssignedWbsService)
{
    Title = "Wbs Assigned";
    this.fieldAssignedWbsService = fieldAssignedWbsService;
}

[ICommand]
async Task GetFieldAssignedWbsListAsync()
{
    if (IsBusy)
        return;
    try
    {
        IsBusy = true;

        var wbsList = await fieldAssignedWbsService.GetFieldAssignedWbsList();

        if (WbsList.Count != 0)
            WbsList.Clear();

        foreach (var wbs in wbsList)
            WbsList.Add(wbs);
    }
    catch (Exception ex)
    {
        Debug.WriteLine(ex);
        await Shell.Current.DisplayAlert("Error!",
            $"Undable to get monkeys: {ex.Message}", "OK");
    }
    finally
    {
        IsBusy = false;
    }
}

}

(CollectionView Binding)

<CollectionView BackgroundColor="Transparent"
                    ItemsSource="{Binding WbsList}"
                    SelectionMode="None">

(Code behind page with incorrect call to Command Method)

public partial class FieldAssignedWbsPage : ContentPage
{
public FieldAssignedWbsPage(FieldAssignedWbsViewModel viewModel)
{
    InitializeComponent();
    BindingContext = viewModel;
    //The following call does not work 
    //Hover message: Non-invocable member... cannot be called like a method
    await viewModel.GetFieldAssignedWbsListCommand();  
}
}

CodePudding user response：

use OnAppearing. You may also need to make the GetFieldAssignedWbsList public

protected override async void OnAppearing()
{
  await viewModel.GetFieldAssignedWbsListCommand.Execute(null);  
}