DropdownButton route

[Aoi-hosizora]

  void _handleTap() {
    final RenderBox itemBox = context.findRenderObject()! as RenderBox;
    final Rect itemRect = itemBox.localToGlobal(Offset.zero) & itemBox.size;
    final TextDirection? textDirection = Directionality.of(context);
    final EdgeInsetsGeometry menuMargin = ButtonTheme.of(context).alignedDropdown
      ? _kAlignedMenuMargin
      : _kUnalignedMenuMargin;

    final List<_MenuItem<T>> menuItems = <_MenuItem<T>>[
    for (int index = 0; index < widget.items!.length; index += 1)
      _MenuItem<T>(
        item: widget.items![index],
        onLayout: (Size size) {
          // If [_dropdownRoute] is null and onLayout is called, this means
          // that performLayout was called on a _DropdownRoute that has not
          // left the widget tree but is already on its way out.
          //
          // Since onLayout is used primarily to collect the desired heights
          // of each menu item before laying them out, not having the _DropdownRoute
          // collect each item's height to lay out is fine since the route is
          // already on its way out.
          if (_dropdownRoute == null)
            return;

          _dropdownRoute!.itemHeights[index] = size.height;
        },
      )
    ];

    assert(_dropdownRoute == null);
    _dropdownRoute = _DropdownRoute<T>(
      items: menuItems,
      buttonRect: menuMargin.resolve(textDirection).inflateRect(itemRect),
      padding: _kMenuItemPadding.resolve(textDirection),
      selectedIndex: _selectedIndex ?? 0,
      elevation: widget.elevation,
      theme: Theme.of(context, shadowThemeOnly: true),
      style: _textStyle!,
      barrierLabel: MaterialLocalizations.of(context).modalBarrierDismissLabel,
      itemHeight: widget.itemHeight,
      dropdownColor: widget.dropdownColor,
    );

    Navigator.push(context, _dropdownRoute!).then<void>((_DropdownRouteResult<T>? newValue) {
      _removeDropdownRoute();
      if (!mounted || newValue == null)
        return;
      if (widget.onChanged != null)
        widget.onChanged!(newValue.result);
    });

    if (widget.onTap != null) {
      widget.onTap!();
    }
  }
``

[Aoi-hosizora]

// class _DropdownRoute<T> extends PopupRoute<_DropdownRouteResult<T>>

  @override
  Widget buildPage(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
    return LayoutBuilder(
      builder: (BuildContext context, BoxConstraints constraints) {
        return _DropdownRoutePage<T>(
          route: this,
          constraints: constraints,
          items: items,
          padding: padding,
          buttonRect: buttonRect,
          selectedIndex: selectedIndex,
          elevation: elevation,
          theme: theme,
          style: style,
          dropdownColor: dropdownColor,
        );
      }
    );
  }

[Aoi-hosizora]

// class _DropdownRoutePage<T> extends StatelessWidget

  @override
  Widget build(BuildContext context) {
    assert(debugCheckHasDirectionality(context));

    // Computing the initialScrollOffset now, before the items have been laid
    // out. This only works if the item heights are effectively fixed, i.e. either
    // DropdownButton.itemHeight is specified or DropdownButton.itemHeight is null
    // and all of the items' intrinsic heights are less than kMinInteractiveDimension.
    // Otherwise the initialScrollOffset is just a rough approximation based on
    // treating the items as if their heights were all equal to kMinInteractveDimension.
    if (route.scrollController == null) {
      final _MenuLimits menuLimits = route.getMenuLimits(buttonRect, constraints.maxHeight, selectedIndex);
      route.scrollController = ScrollController(initialScrollOffset: menuLimits.scrollOffset);
    }

    final TextDirection? textDirection = Directionality.of(context);
    Widget menu = _DropdownMenu<T>(
      route: route,
      padding: padding.resolve(textDirection),
      buttonRect: buttonRect,
      constraints: constraints,
      dropdownColor: dropdownColor,
    );

    if (theme != null)
      menu = Theme(data: theme!, child: menu);

    return MediaQuery.removePadding(
      context: context,
      removeTop: true,
      removeBottom: true,
      removeLeft: true,
      removeRight: true,
      child: Builder(
        builder: (BuildContext context) {
          return CustomSingleChildLayout(
            delegate: _DropdownMenuRouteLayout<T>(
              buttonRect: buttonRect,
              route: route,
              textDirection: textDirection,
            ),
            child: menu,
          );
        },
      ),
    );
  }

[Aoi-hosizora]

See https://github.com/ah-ren/popuproute_ren/blob/master/lib/page/popup_route.dart#L57.

[Aoi-hosizora]

Animation related: https://flutter.dev/docs/development/ui/animations

[Aoi-hosizora]

Container(
  margin: EdgeInsets.only(top: 20),
  height: 400,
  width: 400,
  child: Stack(
    children: [
      Positioned.fill(
        child: GestureDetector(
          onTap: () => print(DateTime.now().toString()),
        ),
      ),
      Positioned(
        right: 0,
        top: -6,
        child: OutlineButton(
          child: Text(
            'test',
            style: TextStyle(color: Colors.white),
          ),
          onPressed: () {
            _show = !_show;
            if (mounted) setState(() {});
          },
        ),
      ),
      AnimatedPositioned(
        left: _show ? 5 : -18,
        top: 120,
        child: AnimatedOpacity(
          opacity: _show ? 1 : 0,
          child: Text(
            '测\n试\n文\n字',
            style: TextStyle(
              color: Colors.white,
              fontSize: 20,
            ),
          ),
          duration: Duration(milliseconds: 500),
        ),
        duration: Duration(milliseconds: 500),
        curve: Flash(showWhenZero: _show),
      ),
    ],
  ),
  color: Colors.black,
)

[Aoi-hosizora]

Done.