dotnet/maui · error · ArgumentNullException

_ = view ?? throw new ArgumentNullException(nameof(view));

Error message

_ = view ?? throw new ArgumentNullException(nameof(view));

What it means

DropEventArgs's public constructor throws ArgumentNullException(nameof(view)) when the DataPackageView argument is null. The constructor is the documented entry point for Drop events; a null data package is treated as a programming error. (An internal overload tolerates a null view and substitutes a fresh DataPackageView.)

Source

Thrown at src/Controls/src/Core/DragAndDrop/DropEventArgs.cs:19

using System;
using Microsoft.Maui.Graphics;

namespace Microsoft.Maui.Controls
{
	/// <summary>
	/// Provides data for the <see cref="DropGestureRecognizer.Drop"/> event.
	/// </summary>
	public class DropEventArgs
	{
		Func<IElement?, Point?>? _getPosition;

		/// <summary>
		/// Initializes a new instance of the <see cref="DropEventArgs"/> class.
		/// </summary>
		/// <param name="view">The data package associated with the drop.</param>
		public DropEventArgs(DataPackageView view)
		{
			_ = view ?? throw new ArgumentNullException(nameof(view));
			Data = view;
		}

		/// <summary>
		/// Initializes a new instance of the <see cref="DropEventArgs"/> class.
		/// </summary>
		/// <param name="view">The data package associated with the drop.</param>
		/// <param name="getPosition">Function used to get the position relative a specified <see cref="IElement"/>.</param>
		/// <param name="platformArgs">The platform-specific data associated with the drag.</param>
		internal DropEventArgs(DataPackageView? view, Func<IElement?, Point?>? getPosition, PlatformDropEventArgs platformArgs)
		{
			Data = view ?? new DataPackageView(new DataPackage());
			_getPosition = getPosition;
			PlatformArgs = platformArgs;
		}

		/// <summary>
		/// Gets the data package associated with the drop event.

View on GitHub (pinned to f377ff1c5e)

Solutions

1. Pass a non-null DataPackageView: wrap a DataPackage with `new DataPackageView(new DataPackage())` if empty.
2. Use the internal overload only if you are framework/platform code and intentionally allow a default package.
3. Null-check before constructing and supply an empty package.

Example fix

// before
var args = new DropEventArgs(null); // throws

// after
var args = new DropEventArgs(new DataPackageView(new DataPackage()));

static DropEventArgs MakeDropArgs(DataPackageView? view) =>
    new(view ?? new DataPackageView(new DataPackage()));

static bool HasDataPackage(DataPackageView? v) => v is not null;

When it happens

Trigger: Constructing `new DropEventArgs(null)` via the public constructor; event-raising code that passes a null DataPackageView.

Common situations: Test code raising Drop events without a data package; refactoring that loses the DataPackageView reference before constructing args.

Related errors

• _ = args ?? throw new ArgumentNullException(nameof(args));
• public ElementEventArgs(Element element) => Element = elemen
• 'selector' cannot be null or whitespace.
• newElement
• ContentLoader

AI-assisted analysis of dotnet/maui@f377ff1c5e (2026-08-13). Data as JSON: /api/errors/12a95b1f138ea2a6. Report an issue: GitHub.