Implement ItemTemplateSelector support on DragDropGridView.ItemsSource

[KarsaOrlong1981]

Fix Issue #4 :
DragDropGridView: DataTemplateSelector Support & Refactoring
• Added full support for ItemTemplateSelector
• Introduced a new BindableProperty and corresponding property for the DataTemplateSelector
• Enhanced handler detection for ScrollView and RefreshView to prevent Android.Runtime.JavaProxyThrowable
exceptions when custom handlers are used that do not derive from UntouchableRefreshViewHandler or UntouchableScrollViewHandler

Please double check:

I'm not sure about this "Dragging behind Items behavior":

dragtest.mp4

Usage:

xmlns:gridLayout="clr-namespace:Sharpnado.Maui.DragDropGridView;assembly=Sharpnado.Maui.DragDropGridView"

<ContentPage.Resources>

    <DataTemplate x:Key="Template1">
        <gridLayout:DragAndDropView>
            <Border BackgroundColor="Red"
                    HeightRequest="148"
                    Padding="0"
                    Margin="4"
                    StrokeThickness="0"
                    StrokeShape="RoundRectangle 4,4,4,4">
                <Label Text="{Binding Content}"
                       HorizontalOptions="Center"
                       VerticalOptions="Center"
                       TextColor="White" />
            </Border>
        </gridLayout:DragAndDropView>
    </DataTemplate>

    <DataTemplate x:Key="Template2">
        <gridLayout:DragAndDropView>
            <Border BackgroundColor="Green"
                    HeightRequest="148"
                    Padding="0"
                    Margin="4"
                    StrokeThickness="0"
                    StrokeShape="RoundRectangle 4,4,4,4">
                <Label Text="{Binding Content}"
                       HorizontalOptions="Center"
                       VerticalOptions="Center"
                       TextColor="White" />
            </Border>
        </gridLayout:DragAndDropView>
    </DataTemplate>

    <DataTemplate x:Key="Template3">
        <gridLayout:DragAndDropView>
            <Border BackgroundColor="Blue"
                    HeightRequest="148"
                    Padding="0"
                    Margin="4"
                    StrokeThickness="0"
                    StrokeShape="RoundRectangle 4,4,4,4">
                <Label Text="{Binding Content}"
                       HorizontalOptions="Center"
                       VerticalOptions="Center"
                       TextColor="White" />
            </Border>
        </gridLayout:DragAndDropView>
    </DataTemplate>

    <DataTemplate x:Key="Template4">
        <gridLayout:DragAndDropView>
            <Border BackgroundColor="Yellow"
                    HeightRequest="148"
                    Padding="0"
                    Margin="4"
                    StrokeThickness="0"
                    StrokeShape="RoundRectangle 4,4,4,4">
                <Label Text="{Binding Content}"
                       HorizontalOptions="Center"
                       VerticalOptions="Center"
                       TextColor="Black" />
            </Border>
        </gridLayout:DragAndDropView>
    </DataTemplate>

    <DataTemplate x:Key="Template5">
        <gridLayout:DragAndDropView>
            <Border BackgroundColor="Purple"
                    HeightRequest="148"
                    Padding="0"
                    Margin="4"
                    StrokeThickness="0"
                    StrokeShape="RoundRectangle 4,4,4,4">
                <Label Text="{Binding Content}"
                       HorizontalOptions="Center"
                       VerticalOptions="Center"
                       TextColor="White" />
            </Border>
        </gridLayout:DragAndDropView>
    </DataTemplate>

    <local:WidgetTemplateSelector x:Key="WidgetSelector"
                                  Template1="{StaticResource Template1}"
                                  Template2="{StaticResource Template2}"
                                  Template3="{StaticResource Template3}"
                                  Template4="{StaticResource Template4}"
                                  Template5="{StaticResource Template5}" />
</ContentPage.Resources>

public class WidgetItem
{
    public string Type { get; set; }
    public string Content { get; set; }
}

public class WidgetTemplateSelector : DataTemplateSelector
{
    public DataTemplate Template1 { get; set; }
    public DataTemplate Template2 { get; set; }
    public DataTemplate Template3 { get; set; }
    public DataTemplate Template4 { get; set; }
    public DataTemplate Template5 { get; set; }

    protected override DataTemplate OnSelectTemplate(object item, BindableObject container)
    {
        var widget = item as WidgetItem;
        if (widget == null) return null;

        return widget.Type switch
        {
            "Type1" => Template1,
            "Type2" => Template2,
            "Type3" => Template3,
            "Type4" => Template4,
            "Type5" => Template5,
            _ => null
        };
    }
}

<ScrollView Background="White">
        <gridLayout:DragDropGridView
            ColumnCount="2"
            ColumnSpacing="4"
            DragAndDropTrigger="LongPress"
            IsDragAndDropEnabled="True"
            ItemTemplateSelector="{StaticResource WidgetSelector}"
            ItemsSource="{Binding OrderedWidgets}"
            RowSpacing="4" />
    </ScrollView>