Make LongPressGestureRecognizer dispatch API public for platform backends

External platform backends (for example Maui.Tizen) can raise tap and pointer
gestures because TapGestureRecognizer.SendTapped and PointerGestureRecognizer.Send*
are public infrastructure APIs. LongPressGestureRecognizer.SendLongPressing and
SendLongPressed were still internal, so an out-of-tree backend could detect a long
press but had no supported way to dispatch it.

Promote both methods to public with [EditorBrowsable(EditorBrowsableState.Never)]
and an ArgumentNullException guard on sender, matching the existing tap/pointer
dispatch APIs exactly. Command execution, event raising, GestureStatus transitions,
State updates, position callback behavior, and all in-box platform call sites are
unchanged.

Adds src/Controls/tests/ExternalGestureBackend, a test-support assembly that is
deliberately excluded from Microsoft.Maui.Controls' InternalsVisibleTo list, so its
fake backend can only compile against the public surface. Demoting either method
back to internal breaks that project's build.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: Redth

docs/design/GestureDispatchForPlatformBackends.md

@@ -0,0 +1,125 @@
+# Gesture dispatch for external platform backends
+
+.NET MAUI ships gesture *recognizers* (`TapGestureRecognizer`, `PointerGestureRecognizer`,
+`LongPressGestureRecognizer`, …) in `Microsoft.Maui.Controls`, and gesture *detection* in the
+per-platform gesture managers under `src/Controls/src/Core/Platform`.
+
+Out-of-tree platform backends — for example [`Maui.Tizen`](https://github.com/Redth/Maui.Tizen) —
+implement their own detection layer and need to raise the recognizer's events. To make that
+possible, each recognizer exposes an infrastructure dispatch surface: `public` methods annotated
+with `[EditorBrowsable(EditorBrowsableState.Never)]` so they are reachable from any assembly but
+stay out of IntelliSense for app authors.
+
+| Recognizer | Dispatch API |
+| ---------- | ------------ |
+| `TapGestureRecognizer` | `SendTapped(View sender, Func<IElement?, Point?>? getPosition = null)` |
+| `PointerGestureRecognizer` | `SendPointerEntered` / `SendPointerExited` / `SendPointerMoved` / `SendPointerPressed` / `SendPointerReleased` |
+| `LongPressGestureRecognizer` | `SendLongPressing(View sender, GestureStatus status, Func<IElement?, Point?>? getPosition = null)` and `SendLongPressed(View sender, Func<IElement?, Point?>? getPosition = null)` |
+| `DragGestureRecognizer` | `SendDragStarting` / `SendDropCompleted` |
+| `DropGestureRecognizer` | `SendDragLeave` / `SendDrop` |
+
+## Rules that apply to every dispatch method
+
+- **`sender` must not be `null`.** Each method throws `ArgumentNullException`; pass the `View` the
+  gesture was detected on.
+- **Call on the UI thread.** Dispatch runs user event handlers and commands synchronously, and it
+  writes bindable properties. Marshal to the dispatcher before calling.
+- **`getPosition` is optional.** Pass `null` when the platform cannot supply a location. Otherwise
+  supply a callback that returns the gesture location *relative to the element passed in*, and the
+  location relative to `sender` when the argument is `null` or is `sender` itself. The callback is
+  invoked lazily by the event args, so keep it cheap and avoid capturing strong references to
+  platform views that may already be disposed.
+- **Only dispatch to recognizers attached to the view.** Enumerate
+  `view.GestureRecognizers.OfType<TRecognizer>()` and honor recognizer configuration such as
+  `NumberOfTouchesRequired`.
+
+## `LongPressGestureRecognizer` contract
+
+`LongPressGestureRecognizer` has two channels:
+
+- `SendLongPressing` sets `LongPressGestureRecognizer.State` and raises `LongPressing` with a
+  `GestureStatus`. It is the state machine.
+- `SendLongPressed` executes `Command` (when `Command.CanExecute(CommandParameter)` is `true`) and
+  raises `LongPressed`. It is the "the long press succeeded" notification and carries
+  `CommandParameter` on the event args.
+
+Backends should follow the same ordering the in-box platforms use:
+
+| Platform signal | Calls |
+| --------------- | ----- |
+| Press recognized | `SendLongPressing(view, GestureStatus.Started, getPosition)` |
+| Press held / moved within `AllowableMovement` | `SendLongPressing(view, GestureStatus.Running, getPosition)` |
+| Press released after the minimum duration | `SendLongPressed(view, getPosition)` **then** `SendLongPressing(view, GestureStatus.Completed, getPosition)` |
+| Press cancelled or failed | `SendLongPressing(view, GestureStatus.Canceled, getPosition)` |
+
+Notes:
+
+- `SendLongPressed` is raised **before** `Completed` so handlers observing `LongPressed` see the
+  gesture result before the terminal state change.
+- A cancelled gesture must **not** raise `LongPressed` and must **not** execute `Command`.
+- `Started`/`Running` are optional for platforms that only surface a single "long press happened"
+  callback. Android and Windows go straight to `SendLongPressed` + `Completed`.
+- `MinimumPressDuration`, `NumberOfTouchesRequired`, and `AllowableMovement` are *inputs* for the
+  backend's detector. MAUI does not enforce them; the backend decides which of them the platform can
+  honor and documents the gaps.
+
+### Example backend
+
+```csharp
+using System;
+using System.Linq;
+using Microsoft.Maui;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Graphics;
+
+public sealed class MyPlatformLongPressHandler
+{
+    readonly View _view;
+
+    public MyPlatformLongPressHandler(View view) => _view = view;
+
+    Func<IElement?, Point?> GetPosition(Point origin) =>
+        relativeTo => relativeTo is null || ReferenceEquals(relativeTo, _view)
+            ? origin
+            : TranslateToElement(origin, relativeTo);
+
+    void OnPlatformLongPress(PlatformLongPressArgs e)
+    {
+        var position = GetPosition(new Point(e.X, e.Y));
+
+        foreach (var recognizer in _view.GestureRecognizers
+                     .OfType<LongPressGestureRecognizer>()
+                     .Where(r => r.NumberOfTouchesRequired == e.TouchCount))
+        {
+            switch (e.State)
+            {
+                case PlatformGestureState.Began:
+                    recognizer.SendLongPressing(_view, GestureStatus.Started, position);
+                    break;
+                case PlatformGestureState.Changed:
+                    recognizer.SendLongPressing(_view, GestureStatus.Running, position);
+                    break;
+                case PlatformGestureState.Ended:
+                    recognizer.SendLongPressed(_view, position);
+                    recognizer.SendLongPressing(_view, GestureStatus.Completed, position);
+                    break;
+                case PlatformGestureState.Cancelled:
+                case PlatformGestureState.Failed:
+                    recognizer.SendLongPressing(_view, GestureStatus.Canceled, position);
+                    break;
+            }
+        }
+    }
+}
+```
+
+## Keeping the contract honest
+
+`src/Controls/tests/ExternalGestureBackend` is a test-support assembly that is deliberately **not**
+listed in `Microsoft.Maui.Controls`'s `InternalsVisibleTo` set. It contains a fake backend that
+drives `LongPressGestureRecognizer` purely through the public dispatch API, so demoting any of these
+methods back to `internal` breaks the build. `LongPressGestureRecognizerExternalBackendTests` in
+`Controls.Core.UnitTests` exercises that fake backend across the full
+`Started` → `Running` → `Completed` / `Canceled` lifecycle.
+
+Add the same coverage whenever a new recognizer gains a dispatch API.

src/Controls/src/Core/LongPressGestureRecognizer.cs

@@ -1,4 +1,5 @@
 using System;
+using System.ComponentModel;
 using System.Windows.Input;
 using Microsoft.Maui.Graphics;
 
@@ -120,10 +121,22 @@ public GestureStatus State
 		public event EventHandler<LongPressingEventArgs>? LongPressing;
 
 		/// <summary>
-		/// Sends the long pressed event and executes the command.
+		/// Executes the associated <see cref="Command"/> and raises the <see cref="LongPressed"/> event.
 		/// </summary>
-		internal void SendLongPressed(View sender, Func<IElement?, Point?>? getPosition = null)
+		/// <param name="sender">The view on which the long press gesture was recognized.</param>
+		/// <param name="getPosition">A function that returns the long press position relative to a specified element.</param>
+		/// <remarks>
+		/// <para>This infrastructure method is intended for gesture platform managers.</para>
+		/// <para>Platform backends should raise this when the press completes successfully, immediately
+		/// followed by <see cref="SendLongPressing(View, GestureStatus, Func{IElement, Point?})"/> with
+		/// <see cref="GestureStatus.Completed"/>. It must be called on the UI thread.</para>
+		/// </remarks>
+		/// <exception cref="ArgumentNullException"><paramref name="sender"/> is <see langword="null"/>.</exception>
+		[EditorBrowsable(EditorBrowsableState.Never)]
+		public void SendLongPressed(View sender, Func<IElement?, Point?>? getPosition = null)
 		{
+			_ = sender ?? throw new ArgumentNullException(nameof(sender));
+
 			var cmd = Command;
 			if (cmd != null && cmd.CanExecute(CommandParameter))
 				cmd.Execute(CommandParameter);
@@ -132,10 +145,24 @@ internal void SendLongPressed(View sender, Func<IElement?, Point?>? getPosition
 		}
 
 		/// <summary>
-		/// Sends the long pressing event with state information.
+		/// Updates <see cref="State"/> and raises the <see cref="LongPressing"/> event.
 		/// </summary>
-		internal void SendLongPressing(View sender, GestureStatus status, Func<IElement?, Point?>? getPosition = null)
+		/// <param name="sender">The view on which the long press gesture is being recognized.</param>
+		/// <param name="status">The current status of the gesture.</param>
+		/// <param name="getPosition">A function that returns the long press position relative to a specified element.</param>
+		/// <remarks>
+		/// <para>This infrastructure method is intended for gesture platform managers.</para>
+		/// <para>Platform backends should raise <see cref="GestureStatus.Started"/> once the press is
+		/// recognized, <see cref="GestureStatus.Running"/> while it is held, and finish with either
+		/// <see cref="GestureStatus.Completed"/> or <see cref="GestureStatus.Canceled"/>. It must be
+		/// called on the UI thread.</para>
+		/// </remarks>
+		/// <exception cref="ArgumentNullException"><paramref name="sender"/> is <see langword="null"/>.</exception>
+		[EditorBrowsable(EditorBrowsableState.Never)]
+		public void SendLongPressing(View sender, GestureStatus status, Func<IElement?, Point?>? getPosition = null)
 		{
+			_ = sender ?? throw new ArgumentNullException(nameof(sender));
+
 			State = status;
 			LongPressing?.Invoke(sender, new LongPressingEventArgs(status, getPosition));
 		}

src/Controls/src/Core/PublicAPI/net-android/PublicAPI.Unshipped.txt

@@ -52,6 +52,8 @@ Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.get -> i
 Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.set -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.get -> int
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.set -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressed(Microsoft.Maui.Controls.View! sender, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressing(Microsoft.Maui.Controls.View! sender, Microsoft.Maui.GestureStatus status, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.State.get -> Microsoft.Maui.GestureStatus
 Microsoft.Maui.Controls.LongPressedEventArgs
 Microsoft.Maui.Controls.LongPressedEventArgs.LongPressedEventArgs(object? parameter) -> void

src/Controls/src/Core/PublicAPI/net-ios/PublicAPI.Unshipped.txt

@@ -32,6 +32,8 @@ Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.get -> i
 Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.set -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.get -> int
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.set -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressed(Microsoft.Maui.Controls.View! sender, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressing(Microsoft.Maui.Controls.View! sender, Microsoft.Maui.GestureStatus status, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.State.get -> Microsoft.Maui.GestureStatus
 Microsoft.Maui.Controls.LongPressedEventArgs
 Microsoft.Maui.Controls.LongPressedEventArgs.LongPressedEventArgs(object? parameter) -> void

src/Controls/src/Core/PublicAPI/net-maccatalyst/PublicAPI.Unshipped.txt

@@ -32,6 +32,8 @@ Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.get -> i
 Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.set -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.get -> int
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.set -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressed(Microsoft.Maui.Controls.View! sender, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressing(Microsoft.Maui.Controls.View! sender, Microsoft.Maui.GestureStatus status, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.State.get -> Microsoft.Maui.GestureStatus
 Microsoft.Maui.Controls.LongPressedEventArgs
 Microsoft.Maui.Controls.LongPressedEventArgs.LongPressedEventArgs(object? parameter) -> void

src/Controls/src/Core/PublicAPI/net-tizen/PublicAPI.Unshipped.txt

@@ -44,6 +44,8 @@ Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.get -> i
 Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.set -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.get -> int
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.set -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressed(Microsoft.Maui.Controls.View! sender, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressing(Microsoft.Maui.Controls.View! sender, Microsoft.Maui.GestureStatus status, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.State.get -> Microsoft.Maui.GestureStatus
 Microsoft.Maui.Controls.LongPressedEventArgs
 Microsoft.Maui.Controls.LongPressedEventArgs.LongPressedEventArgs(object? parameter) -> void

src/Controls/src/Core/PublicAPI/net-windows/PublicAPI.Unshipped.txt

@@ -40,6 +40,8 @@ Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.get -> i
 Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.set -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.get -> int
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.set -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressed(Microsoft.Maui.Controls.View! sender, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressing(Microsoft.Maui.Controls.View! sender, Microsoft.Maui.GestureStatus status, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.State.get -> Microsoft.Maui.GestureStatus
 Microsoft.Maui.Controls.LongPressedEventArgs
 Microsoft.Maui.Controls.LongPressedEventArgs.LongPressedEventArgs(object? parameter) -> void

src/Controls/src/Core/PublicAPI/net/PublicAPI.Unshipped.txt

@@ -61,6 +61,8 @@ Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.get -> i
 Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.set -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.get -> int
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.set -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressed(Microsoft.Maui.Controls.View! sender, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressing(Microsoft.Maui.Controls.View! sender, Microsoft.Maui.GestureStatus status, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.State.get -> Microsoft.Maui.GestureStatus
 Microsoft.Maui.Controls.LongPressedEventArgs
 Microsoft.Maui.Controls.LongPressedEventArgs.LongPressedEventArgs(object? parameter) -> void

src/Controls/src/Core/PublicAPI/netstandard/PublicAPI.Unshipped.txt

@@ -52,6 +52,8 @@ Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.get -> i
 Microsoft.Maui.Controls.LongPressGestureRecognizer.MinimumPressDuration.set -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.get -> int
 Microsoft.Maui.Controls.LongPressGestureRecognizer.NumberOfTouchesRequired.set -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressed(Microsoft.Maui.Controls.View! sender, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
+Microsoft.Maui.Controls.LongPressGestureRecognizer.SendLongPressing(Microsoft.Maui.Controls.View! sender, Microsoft.Maui.GestureStatus status, System.Func<Microsoft.Maui.IElement?, Microsoft.Maui.Graphics.Point?>? getPosition = null) -> void
 Microsoft.Maui.Controls.LongPressGestureRecognizer.State.get -> Microsoft.Maui.GestureStatus
 Microsoft.Maui.Controls.LongPressedEventArgs
 Microsoft.Maui.Controls.LongPressedEventArgs.LongPressedEventArgs(object? parameter) -> void

src/Controls/tests/Core.UnitTests/Controls.Core.UnitTests.csproj

@@ -19,6 +19,7 @@
     <ProjectReference Include="..\..\..\Controls\Maps\src\Controls.Maps.csproj" />
     <ProjectReference Include="..\..\..\Controls\src\Core\Controls.Core.csproj" />
     <ProjectReference Include="..\..\..\Controls\src\Xaml\Controls.Xaml.csproj" />
+    <ProjectReference Include="..\..\..\Controls\tests\ExternalGestureBackend\Controls.Tests.ExternalGestureBackend.csproj" />
     <ProjectReference Include="..\..\..\Core\maps\src\Maps.csproj" />
     <ProjectReference Include="..\..\..\Core\src\Core.csproj" />
     <ProjectReference Include="..\..\..\Essentials\src\Essentials.csproj" />