How to build the sliding bar?

  1. Summary of my problem
    I m trying to create the expandable container opened through the sliding as in OnePlus 7 mobile.

Wrap your Widget in GestureDetector and use onHorizontalDragUpdate

GestureDetector(onHorizontalDragUpdate: (details) {  
  if (details.delta.dx > senstivity) {
    // Right Swipe
    // Sestivity is integer is used when you don't want to mess up vertical drag
  } else if(details.delta.dx < -senstivity){
    //Left Swipe
  }
});