58 lines
2.3 KiB
Dart
58 lines
2.3 KiB
Dart
import 'package:flutter/widgets.dart';
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/// Scroll the nearest scrollable ancestor so [context] is centered.
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///
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/// Uses [Scrollable.ensureVisible] with alignment 0.5 (center).
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/// Runs in a post-frame callback to ensure layout is complete.
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void scrollContextToCenter(BuildContext? context) {
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if (context == null) return;
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WidgetsBinding.instance.addPostFrameCallback((_) {
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if (!context.mounted) return;
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Scrollable.ensureVisible(context, alignment: 0.5, duration: const Duration(milliseconds: 200), curve: Curves.easeOut);
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});
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}
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/// Jump a vertical [ListView] so that [currentIndex] is visible.
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///
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/// Measures the first item (via [firstItemKey]) to get the real item height,
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/// then scrolls to `currentIndex * itemHeight`, clamped to max extent.
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/// Call once after the first build; the callback is a no-op if the key or
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/// controller aren't ready yet.
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void scrollToCurrentItem(ScrollController controller, GlobalKey firstItemKey, int currentIndex) {
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WidgetsBinding.instance.addPostFrameCallback((_) {
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if (!controller.hasClients) return;
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final itemHeight = (firstItemKey.currentContext?.findRenderObject() as RenderBox?)?.size.height;
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if (itemHeight == null) return;
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final maxExtent = controller.position.maxScrollExtent;
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if (!maxExtent.isFinite) return;
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final target = (currentIndex * itemHeight).clamp(0.0, maxExtent);
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controller.jumpTo(target);
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});
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}
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/// Scroll a horizontal list to center the item at the given index.
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///
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/// Assumes items are laid out with [leadingPadding] before the first item,
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/// and each item occupies [itemExtent] pixels (including per-item padding).
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void scrollListToIndex(
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ScrollController controller,
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int index, {
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required double itemExtent,
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double leadingPadding = 12.0,
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bool animate = true,
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}) {
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if (controller.positions.length != 1 || itemExtent <= 0) return;
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final viewport = controller.position.viewportDimension;
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final maxExtent = controller.position.maxScrollExtent;
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if (!viewport.isFinite || !maxExtent.isFinite) return;
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final targetCenter = leadingPadding + (index * itemExtent) + (itemExtent / 2);
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final desiredOffset = (targetCenter - (viewport / 2)).clamp(0.0, maxExtent);
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if (animate) {
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controller.animateTo(desiredOffset, duration: const Duration(milliseconds: 150), curve: Curves.easeOut);
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} else {
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controller.jumpTo(desiredOffset);
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}
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}
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