opt: select (#937)

lib/common/widgets/appbar/appbar.dart

@@ -4,7 +4,7 @@ import 'package:get/get.dart';
 
 class MultiSelectAppBarWidget extends StatelessWidget
     implements PreferredSizeWidget {
-  final MultiSelectMixin ctr;
+  final MultiSelectBase ctr;
   final bool? visible;
   final AppBar child;
   final List<Widget>? children;
@@ -19,8 +19,7 @@ class MultiSelectAppBarWidget extends StatelessWidget
 
   @override
   Widget build(BuildContext context) {
-    final visible = this.visible ?? ctr.enableMultiSelect.value;
-    if (visible) {
+    if (visible ?? ctr.enableMultiSelect.value) {
       return AppBar(
         bottom: child.bottom,
         leading: IconButton(

lib/common/widgets/select_mask.dart

@@ -0,0 +1,34 @@
+import 'package:PiliPlus/common/constants.dart';
+import 'package:flutter/material.dart';
+
+Widget selectMask(ThemeData theme, bool checked) {
+  return AnimatedOpacity(
+    opacity: checked ? 1 : 0,
+    duration: const Duration(milliseconds: 200),
+    child: Container(
+      alignment: Alignment.center,
+      decoration: BoxDecoration(
+        borderRadius: StyleString.mdRadius,
+        color: Colors.black.withValues(alpha: 0.6),
+      ),
+      child: AnimatedScale(
+        scale: checked ? 1 : 0,
+        duration: const Duration(milliseconds: 250),
+        curve: Curves.easeInOut,
+        child: Container(
+          width: 34,
+          height: 34,
+          decoration: BoxDecoration(
+            color: theme.colorScheme.surface.withValues(alpha: 0.8),
+            shape: BoxShape.circle,
+          ),
+          child: Icon(
+            Icons.done_all_outlined,
+            color: theme.colorScheme.primary,
+            semanticLabel: '取消选择',
+          ),
+        ),
+      ),
+    ),
+  );
+}