opt: 图片预览

lib/plugin/pl_gallery/custom_dismissible.dart

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+import 'package:flutter/material.dart';
+
+/// A widget used to dismiss its [child].
+///
+/// Similar to [Dismissible] with some adjustments.
+class CustomDismissible extends StatefulWidget {
+  const CustomDismissible({
+    required this.child,
+    this.onDismissed,
+    this.dismissThreshold = 0.2,
+    this.enabled = true,
+    Key? key,
+  }) : super(key: key);
+
+  final Widget child;
+  final double dismissThreshold;
+  final VoidCallback? onDismissed;
+  final bool enabled;
+
+  @override
+  State<CustomDismissible> createState() => _CustomDismissibleState();
+}
+
+class _CustomDismissibleState extends State<CustomDismissible>
+    with SingleTickerProviderStateMixin {
+  late AnimationController _animateController;
+  late Animation<Offset> _moveAnimation;
+  late Animation<double> _scaleAnimation;
+  late Animation<Decoration> _opacityAnimation;
+
+  double _dragExtent = 0;
+  bool _dragUnderway = false;
+
+  bool get _isActive => _dragUnderway || _animateController.isAnimating;
+
+  @override
+  void initState() {
+    super.initState();
+
+    _animateController = AnimationController(
+      duration: const Duration(milliseconds: 300),
+      vsync: this,
+    );
+
+    _updateMoveAnimation();
+  }
+
+  @override
+  void dispose() {
+    _animateController.dispose();
+
+    super.dispose();
+  }
+
+  void _updateMoveAnimation() {
+    final double end = _dragExtent.sign;
+
+    _moveAnimation = _animateController.drive(
+      Tween<Offset>(
+        begin: Offset.zero,
+        end: Offset(0, end),
+      ),
+    );
+
+    _scaleAnimation = _animateController.drive(Tween<double>(
+      begin: 1,
+      end: 0.5,
+    ));
+
+    _opacityAnimation = DecorationTween(
+      begin: const BoxDecoration(color: Color(0xFF000000)),
+      end: const BoxDecoration(color: Color(0x00000000)),
+    ).animate(_animateController);
+  }
+
+  void _handleDragStart(DragStartDetails details) {
+    _dragUnderway = true;
+
+    if (_animateController.isAnimating) {
+      _dragExtent =
+          _animateController.value * context.size!.height * _dragExtent.sign;
+      _animateController.stop();
+    } else {
+      _dragExtent = 0.0;
+      _animateController.value = 0.0;
+    }
+    setState(_updateMoveAnimation);
+  }
+
+  void _handleDragUpdate(DragUpdateDetails details) {
+    if (!_isActive || _animateController.isAnimating) {
+      return;
+    }
+
+    final double delta = details.primaryDelta!;
+    final double oldDragExtent = _dragExtent;
+
+    if (_dragExtent + delta < 0) {
+      _dragExtent += delta;
+    } else if (_dragExtent + delta > 0) {
+      _dragExtent += delta;
+    }
+
+    if (oldDragExtent.sign != _dragExtent.sign) {
+      setState(_updateMoveAnimation);
+    }
+
+    if (!_animateController.isAnimating) {
+      _animateController.value = _dragExtent.abs() / context.size!.height;
+    }
+  }
+
+  void _handleDragEnd(DragEndDetails details) {
+    if (!_isActive || _animateController.isAnimating) {
+      return;
+    }
+
+    _dragUnderway = false;
+
+    if (_animateController.isCompleted) {
+      return;
+    }
+
+    if (!_animateController.isDismissed) {
+      // if the dragged value exceeded the dismissThreshold, call onDismissed
+      // else animate back to initial position.
+      if (_animateController.value > widget.dismissThreshold) {
+        widget.onDismissed?.call();
+      } else {
+        _animateController.reverse();
+      }
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final Widget content = DecoratedBoxTransition(
+      decoration: _opacityAnimation,
+      child: SlideTransition(
+        position: _moveAnimation,
+        child: ScaleTransition(
+          scale: _scaleAnimation,
+          child: widget.child,
+        ),
+      ),
+    );
+
+    return GestureDetector(
+      behavior: HitTestBehavior.translucent,
+      onVerticalDragStart: widget.enabled ? _handleDragStart : null,
+      onVerticalDragUpdate: widget.enabled ? _handleDragUpdate : null,
+      onVerticalDragEnd: widget.enabled ? _handleDragEnd : null,
+      child: content,
+    );
+  }
+}