opt: 图片预览

lib/plugin/pl_gallery/interactive_viewer_boundary.dart

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+import 'package:flutter/material.dart';
+
+/// A callback for the [InteractiveViewerBoundary] that is called when the scale
+/// changed.
+typedef ScaleChanged = void Function(double scale);
+
+/// Builds an [InteractiveViewer] and provides callbacks that are called when a
+/// horizontal boundary has been hit.
+///
+/// The callbacks are called when an interaction ends by listening to the
+/// [InteractiveViewer.onInteractionEnd] callback.
+class InteractiveViewerBoundary extends StatefulWidget {
+  const InteractiveViewerBoundary({
+    required this.child,
+    required this.boundaryWidth,
+    this.controller,
+    this.onScaleChanged,
+    this.onLeftBoundaryHit,
+    this.onRightBoundaryHit,
+    this.onNoBoundaryHit,
+    this.maxScale,
+    this.minScale,
+    Key? key,
+  }) : super(key: key);
+
+  final Widget child;
+
+  /// The max width this widget can have.
+  ///
+  /// If the [InteractiveViewer] can take up the entire screen width, this
+  /// should be set to `MediaQuery.of(context).size.width`.
+  final double boundaryWidth;
+
+  /// The [TransformationController] for the [InteractiveViewer].
+  final TransformationController? controller;
+
+  /// Called when the scale changed after an interaction ended.
+  final ScaleChanged? onScaleChanged;
+
+  /// Called when the left boundary has been hit after an interaction ended.
+  final VoidCallback? onLeftBoundaryHit;
+
+  /// Called when the right boundary has been hit after an interaction ended.
+  final VoidCallback? onRightBoundaryHit;
+
+  /// Called when no boundary has been hit after an interaction ended.
+  final VoidCallback? onNoBoundaryHit;
+
+  final double? maxScale;
+
+  final double? minScale;
+
+  @override
+  InteractiveViewerBoundaryState createState() =>
+      InteractiveViewerBoundaryState();
+}
+
+class InteractiveViewerBoundaryState extends State<InteractiveViewerBoundary> {
+  TransformationController? _controller;
+
+  double? _scale;
+
+  @override
+  void initState() {
+    super.initState();
+
+    _controller = widget.controller ?? TransformationController();
+  }
+
+  @override
+  void dispose() {
+    _controller!.dispose();
+
+    super.dispose();
+  }
+
+  void _updateBoundaryDetection() {
+    final double scale = _controller!.value.row0[0];
+
+    if (_scale != scale) {
+      // the scale changed
+      _scale = scale;
+      widget.onScaleChanged?.call(scale);
+    }
+
+    if (scale <= 1.01) {
+      // cant hit any boundaries when the child is not scaled
+      return;
+    }
+
+    final double xOffset = _controller!.value.row0[3];
+    final double boundaryWidth = widget.boundaryWidth;
+    final double boundaryEnd = boundaryWidth * scale;
+    final double xPos = boundaryEnd + xOffset;
+
+    if (boundaryEnd.round() == xPos.round()) {
+      // left boundary hit
+      widget.onLeftBoundaryHit?.call();
+    } else if (boundaryWidth.round() == xPos.round()) {
+      // right boundary hit
+      widget.onRightBoundaryHit?.call();
+    } else {
+      widget.onNoBoundaryHit?.call();
+    }
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return InteractiveViewer(
+      maxScale: widget.maxScale!,
+      minScale: widget.minScale!,
+      transformationController: _controller,
+      onInteractionEnd: (_) => _updateBoundaryDetection(),
+      child: widget.child,
+    );
+  }
+}