opt: multiSelect (#935)

lib/common/widgets/appbar/appbar.dart

@@ -0,0 +1,91 @@
+import 'package:PiliPlus/pages/common/multi_select_controller.dart';
+import 'package:flutter/material.dart';
+import 'package:get/get.dart';
+
+class AppBarWidget extends StatelessWidget implements PreferredSizeWidget {
+  const AppBarWidget({
+    required this.child1,
+    required this.child2,
+    required this.visible,
+    super.key,
+  });
+
+  final PreferredSizeWidget child1;
+  final PreferredSizeWidget child2;
+  final bool visible;
+  @override
+  Size get preferredSize => child1.preferredSize;
+
+  @override
+  Widget build(BuildContext context) {
+    return AnimatedSwitcher(
+      duration: const Duration(milliseconds: 500),
+      transitionBuilder: (Widget child, Animation<double> animation) {
+        return ScaleTransition(
+          scale: animation,
+          child: child,
+        );
+      },
+      child: !visible
+          ? KeyedSubtree.wrap(child1, 0)
+          : KeyedSubtree.wrap(child2, 1),
+    );
+  }
+}
+
+class MultiSelectAppBarWidget extends StatelessWidget
+    implements PreferredSizeWidget {
+  final MultiSelectMixin ctr;
+  final bool? visible;
+  final AppBar child;
+  final List<Widget>? children;
+
+  const MultiSelectAppBarWidget({
+    super.key,
+    required this.ctr,
+    this.visible,
+    this.children,
+    required this.child,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    return AppBarWidget(
+      visible: visible ?? ctr.enableMultiSelect.value,
+      child1: child,
+      child2: AppBar(
+        bottom: child.bottom,
+        leading: IconButton(
+          tooltip: '取消',
+          onPressed: ctr.handleSelect,
+          icon: const Icon(Icons.close_outlined),
+        ),
+        title: Obx(() => Text('已选: ${ctr.checkedCount}')),
+        actions: [
+          TextButton(
+            style: TextButton.styleFrom(
+              visualDensity: VisualDensity.compact,
+            ),
+            onPressed: () => ctr.handleSelect(true),
+            child: const Text('全选'),
+          ),
+          ...?children,
+          TextButton(
+            style: TextButton.styleFrom(
+              visualDensity: VisualDensity.compact,
+            ),
+            onPressed: ctr.onConfirm,
+            child: Text(
+              '移除',
+              style: TextStyle(color: Get.theme.colorScheme.error),
+            ),
+          ),
+          const SizedBox(width: 6),
+        ],
+      ),
+    );
+  }
+
+  @override
+  Size get preferredSize => child.preferredSize;
+}