Close back layer programatically [need to document it]

[TenPetr]

It would be great, if you could close or toggle between front and back layers programatically without using BackdropToggleButton. I did not find a way, how to do it.

For example - I am using some filters in this widget and when user select filter, I would like to close back layer automatically, without user need to click on toggle button in the appbar's actions.

If you have any idea, how to implement this with existing code, please let me know.

Thanks for your time and suggestions.

[WieFel]

Hi @TenPetr.
This is obviously possible. Just use the following code snippets in any point of your code (but below BackdropScaffold within the widget tree!):

Backdrop.of(context).revealBackLayer();

to reveal (show) the back layer, and

Backdrop.of(context).concealBackLayer();

to conceal (hide) the back layer.

If you want to use this directly within the widget in which you build your BackdropScaffold, you have to wrap the call to Backdrop.of(context) into a LayoutBuilder, e.g.:

MaterialApp(
      home: BackdropScaffold(
        ...
        frontLayer: Center(
          child: LayoutBuilder(
            builder: (context, constraints) => RaisedButton(
              onPressed: () {
                Backdrop.of(context).concealBackLayer();
              },
              child: Text("Conceal back layer"),
            ),
          ),
        ),
      ),
    );

[TenPetr]

That is amazing! I tried this solution, but I did not have my widget wrapped in the LayoutBuilder, so that is why my code did not work. Thank you so much!

[daadu]

@WieFel Should we put this in README? Under headline "Accessing the internal state of Backdrop".

[WieFel]

@daadu yes, I thought so too!

[daadu]

I am opening this issue until it is put in README. Also Builder should be used instead of LayoutBuilder, which is more generic. Also in the doc and FWoTW video, it specifies the use-case that we want that is - "Need to look up a parent in the same build method".

[daadu]

Also need to specify that the "Builder wrapper" is not mandatory, in case if Backdrop.of is called with separate widget (which has to be the child of BackdropScaffold) it not required as the context passed is of that widget. It is only required if Backdrop.of is called with in the same build method where the root BackdropScaffold is initialized.

This applies to other .of method of InhteritedWidget (which Backdrop is) like - Scaffold.of, MediaQuery.of, Theme.of, etc. This is a general pattern in flutter. New flutter users are not aware of it, since it requires to know how "InhertiedWidgets" work and how "widget tree is built and maintained".

[daadu]

@WieFel Created PR for documenting it. Also @TenPetr is the "Note" clear enough to explain why Builder is required or more explanation with code is required?

[TenPetr]

@daadu Yes, I think I understand.

Also, what I have noticed here, when you have one or more FloatingActionButton, they are still visible, even when back layer is toggled on. Do you think there is any setting or an option, how to hide these or should I just use Backdrop.of(context).isBackLayerConcealed to hide or show them? @WieFel

Thanks a lot!

[daadu]

There are callbacks in BackdropScaffold that you can use - onBackLayerConcealed and onBackLayerRevealed.

[TenPetr]

There are callbacks in BackdropScaffold that you can use - onBackLayerConcealed and onBackLayerRevealed.

Perfect, I will include my code snippet here

onBackLayerRevealed: () => setState(() => areFloatingsVisible = false),
onBackLayerConcealed: () => setState(() => areFloatingsVisible = true),