Redesign and simplify the API to mimic official ListView.builder

[maheshj01]

• [ ] Get rid of item extent
• [ ] AlphabetScrollView should have a controller allowing to add listener and an api to scroll to letter
• [ ] overlay widget should be replaced with a overlay builder
• [ ] Trigger haptic feedback when the selected letter changes.

Current API

 AlphabetScrollView(
              list: list.map((e) => AlphaModel(e)).toList(),
              // isAlphabetsFiltered: false,
              alignment: LetterAlignment.right,
              itemExtent: 50,
              unselectedTextStyle: TextStyle(),
              selectedTextStyle: TextStyle(),
              overlayWidget: (String value){
                return YourWidget();
              },
              itemBuilder: (_, k, id) {
                return ListWidget(),
                );
              },
            )

Proposal

 AlphabetScrollView(
    list: list.map((e) => AlphaModel(e)).toList(),
    alignment: LetterAlignment.right,
    unselectedTextStyle: TextStyle(),
    selectedTextStyle: TextStyle(),
    overlayBuilder: (BuildContext context, String selectedLetter){
       return  Widget(selectedLetter);
     },
     itemBuilder: (_, k, id) {
       return ListWidget();
    },
  );

Sanitary Tests

• [X] Drag/Tap the alphabet should focus an alphabet
• [ ] AlphabetList should avoid letters for which there is no List Item
• [ ] Alphabet List can be aligned on the left/right
• [ ] Tap/Drag animates smoothly to the first element in the List (of selected letters)

[maheshj01]

Proposed Solution

• [ ] Get rid of item extent We should calculate and maintain the offset of each item everytime the widget updates (expensive)

[philitell]

It would also be great if it is possible to set scroll-physics - like for normal ListView e.g.

    physics: const ClampingScrollPhysics(
      parent: AlwaysScrollableScrollPhysics(),
    ),

[maheshj01]

Here are some questions when answered would help getting this issue resolved faster.

• When the widget renders it should have the offset stored in a map for each alphabet so as to quickly jump to the start of the letter. How do we handle lazy loading or the entire should always be in memory?
• Does this widget take unsorted list or should the widget handle it?
• If the list submitted to widget is an object what field should we consider for sorting.

On phone right now will make this detailed soon