Register gesture handlers

⚠️ This is the most common source of bugs when testing gestures.

When using GestureRecognizerTestHelper or MultiTouchTestHelperFactory to test gesture events like Pinch, Scroll, or Pull-to-Refresh, handlers must be registered BEFORE the window is shown.

Register before showing the window

var control = new MyControl();
var window = new Window { Content = control };
window.Show();  // ❌ Show FIRST

// Too late! Gesture recognizers are already initialized
Gestures.AddPinchHandler(control, (s, e) => { /* never called */ });

Recommended setup

var control = new MyControl();

// ✅ Register handlers BEFORE Show()
Gestures.AddPinchHandler(control, (s, e) => {
    Console.WriteLine($"Pinch: Scale={e.Scale}");
});

var window = new Window { Content = control };
window.Show();  // ✅ Show AFTER

// Now gestures will work
var (first, second) = MultiTouchTestHelperFactory.CreatePair();
first.Down(control, new Point(100, 150));
second.Down(control, new Point(200, 150));
// ... gesture events will fire correctly

Why Does This Happen?

Avalonia's gesture recognizers are attached to controls when they enter the visual tree (during Show()). If handlers aren't registered at that point, the gesture recognizer doesn't know to track those events.

Which APIs Are Affected?

API	Affected?	Notes
GestureRecognizerTestHelper	✅ Yes	Uses actual gesture recognizers
MultiTouchTestHelperFactory	✅ Yes	Wraps GestureRecognizerTestHelper
TouchInputSimulator.PinchGesture()	❌ No	Raises events directly via RaiseEvent
GestureSimulator.Pinch()	❌ No	Raises events directly via RaiseEvent
AvaloniaDriver touch actions	✅ Yes	Uses gesture recognizer path

Debugging Tip

If your gesture handlers aren't being called:

1. Check that handlers are registered before window.Show()
2. Verify the control is actually in the visual tree
3. Use GestureSimulator if you just need to raise events without actual recognizers