title: How to create a multi-select gridview-layout like android photo app in Flutter?
body: <p>How do i create a gridview-layout with multi-select feature in Flutter, like android photo app? I was looking for an existing widget but couldn't find one.</p>
  
  <p>What I have at the moment: a gridview-layout with n rows and 2 columns. The cells contain a GridTile-widget with some information and a header text. Now i want to have a functionality like in android photo app, after a long press on one of these tiles, a check-circle appears on the left top corner for all items.</p>
  
  <p>Do i have to build this on my own, or is there an existing Flutter-widget which i didn't find so far?</p>