stretchModes property

[hetthummar]

Flutter added stretchModes properties in FlexibleSpaceBar which allows us to zoom or blur the image when user tries to scroll below minimum limit.

flexibleSpace: FlexibleSpaceBar(
    flexibleSpace: BackgroundFlexibleSpaceBar(
        stretchModes: const [
           StretchMode.zoomBackground,
           StretchMode.blurBackground,
           StretchMode.fadeTitle,
        ],
)

I think it is nice to have this in this library.

[LeonColt]

Hi, @hetthummar
It is a great idea, i am a bit busy right now, feel free if you want pull request.
I will update this library soon if there is no pull request