Recreate Renzo-Olivares's simplistic_editor fix

[domesticmouse]

Replaces #1979

Pre-launch Checklist

• I read the Flutter Style Guide recently, and have followed its advice.
• I signed the CLA.
• I read the Contributors Guide.
• I updated/added relevant documentation (doc comments with ///).
• All existing and new tests are passing.

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[domesticmouse]

@Renzo-Olivares please check that I have recreated #1979 faithfully. Thanks!

[Renzo-Olivares]

LGTM thanks for taking care of this!

[domesticmouse]

@Renzo-Olivares Can the onShare and onSearchWeb be null handlers? Or do we need something more complete?

[Renzo-Olivares]

From my knowledge onShare and onSearchWeb aren't available in stable yet. Should we still add them here?

[domesticmouse]

From my knowledge onShare and onSearchWeb aren't available in stable yet. Should we still add them here?

I'm setting this PR up as a patch to land when the Q4 stable release happens.

Assuming onShare and onSearchWeb are slated to release in the Q4 stable then yup, we should add them to this PR.

[Renzo-Olivares]

In that case then onShare and onSearchWeb should have more complete implementations. Something along these lines. This is taken straight from editable_text.dart in the framework. These default implementations should probably be made more re-usable.

  @override
  bool get searchWebEnabled {
    if (defaultTargetPlatform != TargetPlatform.iOS) {
      return false;
    }

    return !textEditingValue.selection.isCollapsed
        && textEditingValue.selection.textInside(textEditingValue.text).trim() != '';
  }

  @override
  bool get shareEnabled {
    if (defaultTargetPlatform != TargetPlatform.iOS) {
      return false;
    }

    return !textEditingValue.selection.isCollapsed
        && textEditingValue.selection.textInside(textEditingValue.text).trim() != '';
  }

  /// Launch a web search on the current selection,
  /// as in the "Search Web" edit menu button on iOS.
  ///
  /// Currently this is only implemented for iOS.
  Future<void> _searchWebForSelection(SelectionChangedCause cause) async {
    final String text = textEditingValue.selection.textInside(textEditingValue.text);
    if (text.isNotEmpty) {
      await SystemChannels.platform.invokeMethod(
        'SearchWeb.invoke',
        text,
      );
    }
  }

  /// Launch the share interface for the current selection,
  /// as in the "Share" edit menu button on iOS.
  ///
  /// Currently this is only implemented for iOS.
  Future<void> _shareSelection(SelectionChangedCause cause) async {
    final String text = textEditingValue.selection.textInside(textEditingValue.text);
    if (text.isNotEmpty) {
      await SystemChannels.platform.invokeMethod(
        'Share.invoke',
        text,
      );
    }
  }