🧠 Description

I have a ListView.builder (used for a chat screen) with the following properties:

ListView.builder(
  reverse: true,
  controller: _scrollController,
  itemCount: messages.length,
  itemBuilder: (context, index) {
    // each message has a dynamic height
  },
)

Each item (message) has dynamic height, and the list is reversed (reverse: true) so the latest messages appear at the bottom.

I need to scroll or jump to a specific index (or message ID) programmatically — for example, to scroll to message #30 when tapping a “Jump to” button.

What I’ve tried

1. Using:

   _scrollController.jumpTo(offset);
   
   

   But this requires knowing the pixel offset, which is not possible with dynamic item heights.

2. Tried storing widget positions using:

   RenderAbstractViewport.of(box)?.getOffsetToReveal(box, 0.0);
   
   

   This works only for built items (already visible in the viewport).
   Items that are off-screen are not yet built, so their RenderBox is null.

3. Tried using:

   Scrollable.ensureVisible(context);
   
   

   But this also works only if the item is already built and has a valid BuildContext.

4. I cannot use external packages such as:

   • scrollable_positioned_list

   • scroll_to_index
     because of project constraints.

⚠️ Problem

ListView.builder lazily builds only visible items, so it’s impossible to know:

• The pixel offset of unbuilt items (due to dynamic heights).

• How to reliably scroll to a target index or message ID without pre-measuring all heights.

There is no native Flutter API to:

• Query a child’s pixel offset by index before it’s built.

• Request ListView to “jump to index X” natively.

Expected Behavior

A built-in way to:

listViewController.jumpToIndex(int index, {Alignment alignment = Alignment.center});

that:

• Works with reverse: true

• Supports dynamic heights

• Handles unbuilt (off-screen) items gracefully