efficient_indexed_stack #

Flutter's IndexedStack widget initializes the given children immediately.

This package handle initialization process so that children gets built lazily.

Minimal usage;

LazyIndexedStack(
  index: index,
  itemCount: itemCount,
  itemBuilder: (_, index) => MyCoolWidget(
    index,
    key: GlobalKey(), // << IMPORTANT
  ),
),

How many children initialized? #

You can set keepAliveDistance parameter to decide how many indices must be alive.

LazyIndexedStack(
  keepAliveDistance: 4,
  index: activeIndex,
  itemCount: itemCount,
  itemBuilder: (_, index) => MyCoolWidget(
    index,
    key: GlobalKey(), // << IMPORTANT
  ),
),

Which indices are alive? #

You can set indexCalculationStrategy parameter to decide which indices should be alive.

• IndexCalculationStrategy.aroundCurrentIndex

aroundCurrentIndex option initializes the current index and the indices before and after that based on keepAliveDistance

LazyIndexedStack(
  indexCalculationStrategy: IndexCalculationStrategy.aroundCurrentIndex,
  keepAliveDistance: 3,
  index: 4,
  itemCount: 10,
  itemBuilder: (_, index) => MyCoolWidget(
    index,
    key: GlobalKey(), // << IMPORTANT
  ),
),

// 0, (1), (2), (3), [4], (5), (6), (7), 8, 9

• IndexCalculationStrategy.beforeCurrentIndex

LazyIndexedStack(
  indexCalculationStrategy: IndexCalculationStrategy.beforeCurrentIndex,
  keepAliveDistance: 3,
  index: 4,
  itemCount: 10,
  itemBuilder: (_, index) => MyCoolWidget(
    index,
    key: GlobalKey(), // << IMPORTANT
  ),
),

// 0, (1), (2), (3), [4], 5, 7, 8, 9

• IndexCalculationStrategy.afterCurrentIndex

LazyIndexedStack(
  indexCalculationStrategy: IndexCalculationStrategy.afterCurrentIndex,
  keepAliveDistance: 3,
  index: 4,
  itemCount: 10,
  itemBuilder: (_, index) => MyCoolWidget(
    index,
    key: GlobalKey(), // << IMPORTANT
  ),
),

// 0, 1, 2, 3, [4], (5), (7), (8), 9

Once you update the current index. Only the new indices are intialized and the others gets disposed.