flutter contextual action bar(cab)

a contextual action bar workaround for flutter.

cab & flutter

contextual action bar (cab) is a top app bar that replace the application app bar to provide contextual actions to selected items. check the material implementation and requirement here

flutter does not natively support cab yet. see issue
until cab is natively supported, this package should provide you with an elegant way to implement the contextual action bar in flutter.

how it works

• contextualscaffold or contextualscrollview(for slivers)
• contextualappbar
• contextualaction
• contextualactionwidget

contextualscaffold<?>

the contextualscaffold<?> is similar to the normal material scaffold except that it also takes
a required contextualappbar.

contextualscaffold<?>(
      contextualappbar: contextualappbar(),
      appbar: appbar(),
      body: body(),
    )

you can provide multiple contextualscaffold as needed

contextualscrollview<?>

the contextualscrollview<?> is similar to the normal nestedscrollview except that it also takes a required contextualappbar.

 contextualscrollview<?>(
     contextualappbar: contextualappbar(),
     headersliverbuilder: (buildcontext context, bool innerboxisscrolled) => [],
     body: body(),
  )
   

the contextualscrollview is used to add first class support for silvers although contextualscaffold can also be used with nestedscrollview check the whatsapp example for complete usage.

contextualappbar<?>

the contextualappbar<?> is similar to the normal material appbar but takes a counterbuilder instead of title and also a contextualactions instead of actions.

 contextualappbar(
      counterbuilder: (int itemscount){
        return text("$itemscount selected");
      },
      contextualactions: <contextualaction>[],
    )

contextualaction<?>

the contextualaction<?> allows you to take actions on the selected items, with the help of itemshandler callback.

contextualaction(
            itemshandler: (list<?> items) {
              items.foreach((item) {
                scaffold.of(context).showsnackbar(snackbar(
                  content: text("$item saved"),
                ));
              });
            },
            child: icon(icons.save),
          ),

contextualactionwidget<?>

you can use the contextualactionwidget anywhere in the contextualactionscaffold or contextualscrollview<?> body to notify contextualactionscaffold or contextualscrollview<?> respectively, that an item have been selected in order to show the contextualappbar.

   contextualactionwidget(
          data: ?,
          child: childwidget(),
        )

note: it is important that the child widget does not handle onlongpress.

a closer look at contextualactionwidget<?>

the contextualactionwidget<?> takes other optional parameters like

• selectedcolor
• selectedwidget
• unselectedwidget

the selectedcolor is the color of the background for the selected item, it defaults to the splash color, if not provided. the selectedcolor works well with listtile.

selectedwidget and unselectedwidget are stacked on top of the provided child widget. by default, they are positioned at the center of the provided child widget.
since they are stacked, you can use row, align, positioned widget or any other combination of widgets to position them where desired.

the selectedwidget is shown when the actionmode is enabled and the item is selected, while the unselectedwidget is shown when actionmode is enabled and the item is not selected. see example(status_saver) image below with both the selectedwidget and unselectedwidget aligned to the top-right corner.

actionmode in contextual action bar

this contextual action bar workaround does not support zero item in the actionmode.

• use the actionmode.additem<?> to add an item to the selected items. if this is the first selection, the actionmode is will be enabled.
• use the actionmode.additems<?> to add a list of items.
• use the actionmode.disable<?> to disable and deselect all selected items.
• use the actionmode.enabledstream<?> to emit true or false depending on if the action mode is enabled or disabled respectively.

note: in most cases, you won’t need to use actionmode.disable<?> because the package already do that for you where needed.