No pointer-down event before pointer-up in Flutter: Causes and How to Fix

Identify the Lifecycle of Pointer Events

• Ensure that the hierarchy of your widget tree is configured correctly to handle pointer events properly. This often means reviewing your use of gesture detectors and ensuring they are not obscured by other widgets unintentionally.

 

• Inspect the flow of pointer events from the `HitTestBehavior` to ensure correct capturing of these events. Adjust `hitTestBehavior` in `GestureDetector` as needed to ensure the desired behavior: `HitTestBehavior.opaque`, `HitTestBehavior.deferToChild`, or `HitTestBehavior.translucent` might be necessary.

Adjust the Gesture Detector Configuration

• Use `GestureDetector` to wrap the widgets that you expect to capture the pointer-down and pointer-up events. If you're missing pointer down events, this usually indicates that the `GestureDetector` was not initialized before the screen rendered, or that another widget might be absorbing these events.

 

• Consider setting the `onPanStart`, `onPanUpdate`, and `onPanEnd` if you're handling complex gestures needing more than just tap or double-tap events.

Ensure Clean Gesture Implementations

• Make sure that your gesture callback methods are implemented fully. Partial implementation might lead to unpredicted results regarding pointer events. For instance:

  GestureDetector(
    onTapDown: (details) {
      // Handle pointer down event
    },
    onTapUp: (details) {
      // Handle pointer up event
    },
    child: YourWidget(),
  )
  

 

• If you use `Listener` widget, ensure that you correctly implement all necessary pointer event handlers as required: `onPointerDown`, `onPointerMove`, `onPointerUp`, etc., and validate they are being triggered as expected.

Debug Pointer Event Flow

• Utilize the Flutter DevTools or add `print` outputs to track the lifecycle of pointer events within your app. This includes starting the observation from the root view to specific elements that require the pointer interactions.

 

• Extract detailed insights about which elements are intercepting these events and the order of their execution. This can clarify if some views have an incorrect event priority.

Troubleshoot Event Absorption

• Verify that parent widgets are not unintentionally absorbing pointer events. Use properties like `behavior: HitTestBehavior.translucent` on `GestureDetector` to allow events to pass through to layers behind.

 

• In cases where custom widgets or nested structures are complex, assess if `AbsorbPointer` is being used anywhere inappropriately. Even if not used directly, custom coding logic may inadvertently absorb these events.

Consider PointerInterceptor Packages

• If the built-in Flutter mechanisms are insufficient due to the complexity of your UI, evaluate using community-developed packages such as `super_tooltip` or `pointer_interceptor` that could resolve or better handle layered event delegation.