XAML, Binding, Source and Path

Question

I am learning to understand, how the binding mechanism works in XAML for .NET MAUI. I am assuming this is the same for all XAML projects, WPF, MAUI etc.

At the end is the whole XAML.

This XAML works fine:

<Button WidthRequest="150" Text="Add Activity" 
                Command="{Binding AddActivityEntityCommand}"
                IsEnabled="{Binding IsNotBusy}"
                Grid.Row="2"
                Margin="8"/>

• Is the reason why this works because the Button is part of the ContentPage, which has it's x:DataType set to MainPageViewModel, which is where the command lives?

• The Binding is set to AddActivityEntityCommand, while the actual method signature is
  async Task AddActivityEntityAsync(). How is this resolved? Since it obviously doesn't match the name, but it works. And what are the method signature requirements for this to work/being recognized?

This on the other hand, doesn't just work as easy out of the box:

<Label HorizontalOptions="End" TextColor="Red" Padding="0,0,10,0" Text="🗑" 
       IsVisible="{Binding IsSynchronized}">
            <Label.GestureRecognizers>
                 <TapGestureRecognizer 
                       Command="{Binding Source={x:Type viewmodel:MainPageViewModel},
                                            Path=DeleteActivityCommand}" />
            </Label.GestureRecognizers>
 </Label>

• In this context, adding Command="{Binding DeleteActivityCommand} doesn't work, because it derives its Path from <DataTemplate x:DataType="model:ActivityEntity">, I am assuming, which is the data object and not the ViewModel, where the command actually is.
• The problem here is, that as soon as I enter this XAML Command="{Binding Source={x:Type viewmodel:MainPageViewModel}, Path=DeleteActivityCommand}", the CollectionView shows empty and there is an unhandled exception thrown when the view is loaded:

System.Reflection.TargetException: Object does not match target type.

• The method signature for this command is this async Task DeleteActivityAsync()

What am I missing?

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage
    x:Class="OnesieMobile.View.MainPage"
    xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:model="clr-namespace:OnesieMobile.Model"
    xmlns:viewmodel="clr-namespace:OnesieMobile.ViewModel"
    x:DataType="viewmodel:MainPageViewModel"
    Title="{Binding Title}">
    <Grid
        ColumnDefinitions="*"
        RowDefinitions="20,50,50,*"
        RowSpacing="0">
        <Label HorizontalOptions="End" Margin="10,0,10,0"  Text="{Binding CurrentDateTime}" Grid.Row="0"/>
        <Entry Margin="10,0,10,0" 
            Grid.Row="1"  x:Name="entryNewActivity" 
            Placeholder="New Activityssss" HeightRequest="30" Text="{Binding NewActivityTitle}" />

        <Button WidthRequest="150" Text="Add Activity" 
                    Command="{Binding AddActivityEntityCommand}"
                    IsEnabled="{Binding IsNotBusy}"
                    Grid.Row="2"
                    Margin="8"/>

        <CollectionView
            Grid.Row="3"
                ItemsSource="{Binding ActivityEntities}"
                SelectionMode="None">
            <CollectionView.ItemTemplate>
                <DataTemplate x:DataType="model:ActivityEntity">
                    <Grid Padding="10,0,10,0">
                        <Frame Style="{StaticResource CardView}">
                            <Grid  ColumnDefinitions="*,30,50">
                                <StackLayout Padding="10,5,0,0" Grid.Column="0">
                                    <Label Text="{Binding Title}"  />
                                </StackLayout>
                                <StackLayout Padding="10,5,0,0" Grid.Column="1">
                                    <Label HorizontalOptions="End" TextColor="Red"
                                           Padding="0,0,10,0" Text="🗑" IsVisible="{Binding IsSynchronized}"  >
                                        <Label.GestureRecognizers>
                                            <TapGestureRecognizer
                                                Command="{Binding Source={x:Type viewmodel:MainPageViewModel},
                                                Path=DeleteActivityCommand}" />
                                        </Label.GestureRecognizers>
                                    </Label>
                                </StackLayout>
                                <StackLayout Padding="10,5,0,0" Grid.Column="2">
                                    <Label HorizontalOptions="End" 
                                           Padding="0,0,10,0" Text="✔" IsVisible="{Binding IsSynchronized}"  />
                                </StackLayout>
                            </Grid>
                        </Frame>
                    </Grid>
                </DataTemplate>
            </CollectionView.ItemTemplate>
        </CollectionView>
        <ActivityIndicator IsVisible="{Binding IsBusy}"
                               IsRunning="{Binding IsBusy}"
                               HorizontalOptions="FillAndExpand"
                               VerticalOptions="CenterAndExpand"
                               Grid.RowSpan="3"
                               Grid.ColumnSpan="2"/>

    </Grid>
</ContentPage>

Update:
MainPageViewModel.cs contains these Commands

[ICommand]
async Task DeleteActivityAsync()
{
}


[ICommand]
async Task AddActivityEntityAsync()
{
}

Answer 1

Inside an item template, there are several ways to refer to the original BindingContext. I like to do it by getting it from the collection itself:

<CollectionView x:Name="myCollection" ...>
    ...
    <CollectionView.ItemTemplate>
        ...
        Command="{Binding Source={x:Reference myCollection},
                  Path=BindingContext.DeleteActivityCommand}" />

---

FUTURE TBD:

I don't like the command name not existing anywhere in the implementing code. Hopefully there will eventually be a way to specify the command name in the ICommand attribute, to make it obvious:

// This won't work today.
[ICommand Name="DeleteActivityCommand"]
...

For now, we have to learn [ICommand]'s magic naming rules, which seem to be "Remove Async from end (if present); Add Command to end".