Fixed the drag and drop between ListViews

[jpcassano]

Description

The current drag and drop between ListViews continually duplicates the contact being dragged and does not remove the contact from the original list. This fix ensures that a contact will only show up in one of the ListViews at any given time.

Motivation and Context

Developers should have an example of a working drag and drop between two ListViews

How Has This Been Tested?

This logic has been manually tested to verify that a contact can be moved between ListViews.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

[jpcassano]

@microsoft-github-policy-service agree

[Copilot]

Pull Request Overview

This PR fixes the drag-and-drop logic between two ListViews so that a contact is moved (not duplicated) and removed from its original list.

• Unified drag-start handling into ListView_DragItemsStarting and switched from string concatenation to JSON serialization.
• Updated ListView_Drop to deserialize a list of Contact objects and correctly insert/move them.
• Removed the old Target_DragItemsStarting handler and updated XAML to bind both ListViews to the new drag-start event.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
WinUIGallery/Samples/ControlPages/ListViewPage.xaml.cs	Switched to JSON-based drag data, renamed handler, updated drop logic
WinUIGallery/Samples/ControlPages/ListViewPage.xaml	Updated DragItemsStarting bindings to the new unified handler

[Copilot]

Deserialization can return null, leading to a NullReferenceException in the subsequent foreach. Add a null check or default to an empty list before iterating.

Suggested change

	var contactsToMove = JsonSerializer.Deserialize<List<Contact>>(contactsToMoveAsJson);
	var contactsToMove = JsonSerializer.Deserialize<List<Contact>>(contactsToMoveAsJson) ?? new List<Contact>();

[Zakariathr22]

You're currently using JsonSerializer.Serialize / Deserialize to pass drag data (List<Contact>) between ListView_DragItemsStarting and ListView_Drop. Since this drag-and-drop is strictly in-app, this adds unnecessary serialization overhead.

Use DataPackage.Properties instead of JSON

Ultimately, I defer to @marcelwgn’s opinion on this.

[Zakariathr22]

Suggested change

	var contactsToMoveAsJson = JsonSerializer.Serialize(contactsToMove);
	e.Data.SetText(contactsToMoveAsJson);
	e.Data.Properties["contacts"] = contactsToMove;

[Zakariathr22]

Suggested change

	var contactsToMoveAsJson = await e.DataView.GetTextAsync();
	var contactsToMove = JsonSerializer.Deserialize<List<Contact>>(contactsToMoveAsJson);
	var contactsToMove = (List<Contact>)e.DataView.Properties["contacts"];

[marcelwgn]

@jpcassano Thank you for creating this PR. Is it intentional you closed this PR or would you like to continue working on this?

[jpcassano]

I reopened the issue and updated the code to use the DataPackage properties. In my initial commit I saw that the original author chose to use StandardDataFormats.Text and it may not have been the best choice but I did not want to deviate much from that code while fixing the bug.

[marcelwgn]

Thank you for making this contribution and adjusting the code as suggested! @Zakariathr22 the code looks good to me but would also like your opinion on this.

[marcelwgn]

/azp run

[Zakariathr22]

Just remove the unused namespaces
Otherwise, it looks good to me

[marcelwgn]

/azp run