'Flutter - How can i make full height with scroll as a SliverAppBar?

On my layout I made like 2 main widgets. Both of them is expanded widgets. First One is holding welcome message and a input. Second one will be my main content. When i scroll second one i want to first one will disappear and my second widget (main content) will be full screen as SliverAppBar. I tried use SliverAppBar. But SliverAppBar's flexibleSpaces just accepting Image and title. How can i make it ? Thanks for answers!

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Solution 1:[1]

You can use SliverPersistentHeader with SliverPersistentHeaderDelegate in slivers attribute of SliverAppbar as mentioned in this Answer

Sources

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Source: Stack Overflow

Solution Source
Solution 1 Junaid Khalid