[RC1] Implement Platform Args for Drag and Drop EventArgs

[tj-devel709]

Description of Change

This PR exposes platform-specific properties from Drag and Drop Maui Gestures to our customers allowing more customization of Drag and Drop interactions. There are five different events related to drag and drop gestures that use four different EventArg classes that will now contain the following classes:

PlatformDragStartingEventArgs

iOS / Catalyst

UIKit.UIView? Sender { get; }
UIKit.UIDragInteraction DragInteraction { get; }
UIKit.IUIDragSession DragSession { get; }
SetItemProvider (Foundation.NSItemProvider itemProvider)
SetPreviewProvider(Func<UIKit.UIDragPreview?> previewProvider)
SetDragItems(UIDragItem[] dragItems)

Android

Android.Views.View Sender { get; }
Android.Views.MotionEvent MotionEvent { get; }
SetDragShadowBuilder(Android.Views.View.DragShadowBuilder dragShadowBuilder)
SetClipData(Android.Content.ClipData clipData)

Windows

Microsoft.UI.Xaml.UIElement Sender { get; }
Microsoft.UI.Xaml.DragStartingEventArgs DragStartingEventArgs { get; }
bool Handled { get; set; }

---

PlatformDropCompletedEventArgs

iOS / Catalyst

UIKit.UIView? Sender { get; }
UIKit.UIDragInteraction? DragInteraction { get; }
UIKit.IUIDragSession? DragSession { get; }
UIKit.UIDropOperation? DropOperation { get; }
UIKit.UIDropInteraction? DropInteraction { get; }
UIKit.IUIDropSession? DropSession { get; }

Android

Android.Views.View Sender { get; }
Android.Views.DragEvent DragEvent { get; }

Windows

Microsoft.UI.Xaml.UIElement Sender { get; }
Microsoft.UI.Xaml.DropCompletedEventArgs DropCompletedEventArgs { get; }

---

PlatformDropEventArgs

iOS / Catalyst

UIKit.UIView? Sender { get; }
UIKit.UIDropInteraction? DropInteraction { get; }
UIKit.IUIDropSession? DropSession { get; }

Android

Android.Views.View Sender { get; }
Android.Views.DragEvent DragEvent { get; }

Windows

object Sender { get; }
Microsoft.UI.Xaml.DragEventArgs DragEventArgs { get; }

---

PlatformDragEventArgs

iOS / Catalyst

UIKit.UIView? Sender { get; }
UIKit.UIDropInteraction? DropInteraction { get; }
UIKit.IUIDropSession? DropSession { get; }
SetDropProposal(UIKit.UIDropProposal dropProposal)

Android

Android.Views.View Sender { get; }
Android.Views.DragEvent DragEvent { get; }

Windows

object Sender { get; }
Microsoft.UI.Xaml.DragEventArgs DragEventArgs { get; }
bool Handled { get; set;}

---

Sample

Showing overwriting the drag Shadow on iOS

UITest added

DragNDropiOSUITestDemo.mov

Issues Fixed

Fixes #16992

[mattleibow]

Quite a few changes here, so I just wanted to drop a review so that I don't go down a path that was already discussed. My main issues are:

• the apparent "not super required" platform args in the ctors of the event args. Should we add those to banned apis so we don't use it
• the total change of the way Handled is now working. This is potentially more breaking and also I am thinking it is still useful on other platforms... maybe?

[mattleibow]

Should this be Microsoft.UI.Xaml.UIElement?

[tj-devel709]

Some of the calling methods used just have their sender type as object as such:

void HandleDrop(object sender, Microsoft.UI.Xaml.DragEventArgs e)
{ ... }

[tj-devel709]

I could type cast and check for Microsoft.UI.Xaml.UIElement, but I was not sure if we expect that every time or if there was a reason for the 'object'

[mattleibow]

Sender should be the object you are attaching to, so if they are all UIElement, maybe we can keep it consistent

[mattleibow]

Same as above, this probably should be UIElement - even though it is object. The events are only available on UIElement so should never be anything other than element.

[mattleibow]

A few last comments, but looking good. It is more defensive decision making for the func... Not sure if it will cause issues with memory leaks or something. Should be fine, but we can always add an API in RC2 but we can't really take away.

[mattleibow]

Same as above, this probably should be UIElement - even though it is object. The events are only available on UIElement so should never be anything other than element.

[dalexsoto]

❤️