OnTap PDF to some buttons appear

[VanessaSwerts]

In the application I am developing, I needed that when I click on the PDF just once (onTap), some buttons appear under the PDF. But InkWell and gestureDetector are not working with PDFView. How could I implement gestureRecognizers to do this?

[endigo]

You can use the following code .

gestureRecognizers: Set()
              ..add(
                  Factory<TapGestureRecognizer>(() => TapGestureRecognizer()
                    ..onTapDown = (tap) {
                      print("This one prints");
                    })),

[jerilMJ]

onTapDown has a slight delay as compared to onTap so it may seem undesirable in some cases. I was working on a workaround and I have finally got a satisfactory result. This should detect taps while letting through other gestures. It involves extending the OneSequenceGestureRecognizer class and overriding its methods.

Here is the code:

class CustomTapGestureRecognizer extends OneSequenceGestureRecognizer {
  int _selectedPointer;

  // Initial Position of selected pointer
  Offset _initialPos;

  // Timestamp of first pointer (selected) update
  Duration _first;

  // Timestamp of latest pointer (selected) update
  Duration _last;

  // Signifies that the event is potentially a tap
  bool _isPotentiallyTap = false;

  // For future taps
  bool _isGoingToFire = false;

  Function onTap;

  // Reset everything for a new session
  void _resetState() {
    _isGoingToFire = false;
    _isPotentiallyTap = false;
    _selectedPointer = null;
    _initialPos = null;
    _first = null;
    _last = null;
  }

  @override
  void addPointer(PointerDownEvent event) {
    startTrackingPointer(event.pointer);
    if (_selectedPointer == null) {
      // Select the first pointer that comes through
      _selectedPointer = event.pointer;
      _isPotentiallyTap = true;
    } else {
      // Multiple pointers on the screen which means it's not a tap
      _selectedPointer = null;
      _isPotentiallyTap = false;
    }

    // Accept all. Rejecting might lead to other gestures not working
    resolve(GestureDisposition.accepted);

    // If previous pointer was going to fire [onTap], stop it.
    // Used to prevent onTap being fired on multi-tap.
    if (_isGoingToFire) {
      _resetState();
    }
  }

  @override
  String get debugDescription => 'only one pointer recognizer';

  @override
  void didStopTrackingLastPointer(int pointer) {}

  @override
  void handleEvent(PointerEvent event) {
    // onPointerUp, see if it moved and see the duration of its
    // interaction on the screen. If it moved, it's not a tap.
    // If its duration is more than 125 milliseconds (default
    // Android tapTimeout), it's not a tap.
    if (!event.down && event.pointer == _selectedPointer) {
      _last = event.timeStamp;

      if (event.localPosition.distanceSquared ==
              (_initialPos?.distanceSquared ??
                  event.localPosition.distanceSquared) &&
          (_last.inMilliseconds - _first.inMilliseconds) <= 125) {
        _isGoingToFire = true;

        // Presenting a slight delay to consider multi-tap case
        Future.delayed(const Duration(milliseconds: 250), () {
          if (_isPotentiallyTap) {
            onTap();
          }
          _resetState();
        });
      } else {
        _resetState();
      }
    } else if (_initialPos == null) {
      // Get initialPos and time
      _initialPos = event.localPosition;
      _first = event.timeStamp;
    }
  }
}

And now, add it to the gestureRecognizers argument of PDFView:

  PDFView(
               ....
                gestureRecognizers: Set()
                  ..add(
                    Factory<CustomTapGestureRecognizer>(
                      () => CustomTapGestureRecognizer()
                        ..onTap = () {
                          // make the buttons appear here
                        },
                    ),
                  ),
  ),

It might seem a bit long but it works pretty good. Hope it helps! :)

[VanessaSwerts]

Thank you so much for the help of both , its works very well.