Selecting text sometimes throws exception

[dineshnaikb]

The following _TypeError was thrown while handling a gesture:
Null check operator used on a null value

When the exception was thrown, this was the stack:
#0      SelectableRegionState._handleSelectionEndHandleDragUpdate (package:flutter/src/widgets/selectable_region.dart:839:22)
selectable_region.dart:839
#1      SelectionOverlay._handleEndHandleDragUpdate (package:flutter/src/widgets/text_selection.dart:1211:28)
text_selection.dart:1211
#2      DragGestureRecognizer._checkUpdate.<anonymous closure> (package:flutter/src/gestures/monodrag.dart:806:55)
monodrag.dart:806
#3      GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:344:24)
recognizer.dart:344
#4      DragGestureRecognizer._checkUpdate (package:flutter/src/gestures/monodrag.dart:806:7)
monodrag.dart:806
#5      DragGestureRecognizer.handleEvent (package:flutter/src/gestures/monodrag.dart:652:11)
monodrag.dart:652
#6      PointerRouter._dispatch (package:flutter/src/gestures/pointer_router.dart:98:12)
pointer_router.dart:98
#7      PointerRouter._dispatchEventToRoutes.<anonymous closure> (package:flutter/src/gestures/pointer_router.dart:143:9)
pointer_router.dart:143
#8      _LinkedHashMapMixin.forEach (dart:collection-patch/compact_hash.dart:633:13)
compact_hash.dart:633
#9      PointerRouter._dispatchEventToRoutes (package:flutter/src/gestures/pointer_router.dart:141:18)
pointer_router.dart:141
#10     PointerRouter.route (package:flutter/src/gestures/pointer_router.dart:127:7)
pointer_router.dart:127
#11     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:495:19)
binding.dart:495
#12     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:475:22)
binding.dart:475
#13     RendererBinding.dispatchEvent (package:flutter/src/rendering/binding.dart:425:11)
binding.dart:425
#14     GestureBinding._handlePointerEventImmediately (package:flutter/src/gestures/binding.dart:420:7)
binding.dart:420
#15     GestureBinding.handlePointerEvent (package:flutter/src/gestures/binding.dart:383:5)
binding.dart:383
#16     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:330:7)
binding.dart:330
#17     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:299:9)
binding.dart:299
#18     _invoke1 (dart:ui/hooks.dart:328:13)
hooks.dart:328

user action

trying long press and dragged the text for select and crashed

crash point

---

_selectionOverlay!.updateMagnifier(_buildInfoForMagnifier(
                           ^
  details.globalPosition,
  _selectionDelegate.value.endSelectionPoint!,
));

file

selectable_region.dart:839

@espresso3389

[espresso3389]

This is a known issue but it is inside the Flutter code. I don't know what is the actual cause because it's too difficult to debug the issue correctly. But it seems that Flutter's text selection system does not expect scrolling/zooming of the selection coordinates.

Anyway, the exception causes selection loss but it actually causes no critical issues.

[espresso3389]

Related: #4

[espresso3389]

1.0.83 contains minor fix to make the text selection stabler.

[dineshnaikb]