flutter: context cleanup batch 7 — accept invitation + delete family + loading/qr const cleanup

[zensgit]

• accept_invitation_dialog: capture messenger/navigator; mounted guards; remove unused import
• delete_family_dialog: capture messenger/navigator; use mounted; underscore ref.refresh; switch navigator/messenger usages
• loading_indicator/qr_code_generator: remove invalid consts

All tests green locally; analyzer warnings reduced; remaining warnings tracked separately.

[Copilot]

Pull Request Overview

This PR performs context cleanup in Flutter dialog and widget components to improve code quality and reduce analyzer warnings. The changes focus on capturing Navigator and ScaffoldMessenger instances early, using proper mounted guards, and removing invalid const keywords.

• Capture Navigator and ScaffoldMessenger instances to avoid context usage after disposal
• Replace context.mounted checks with proper mounted property usage
• Remove unnecessary const keywords from widgets with dynamic properties

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
loading_indicator.dart	Remove invalid const keywords from SizedBox widgets that have dynamic properties
qr_code_generator.dart	Remove const keywords from Center and CircularProgressIndicator widgets
delete_family_dialog.dart	Capture navigator/messenger early, use mounted guards, and underscore unused refresh results
accept_invitation_dialog.dart	Remove unused import, capture messenger/navigator, and replace utility calls with direct SnackBar usage

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[gemini-code-assist]

Summary of Changes

Hello @zensgit, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

此拉取请求主要侧重于 Flutter 对话框中的上下文清理和代码优化。它通过在异步操作前捕获 ScaffoldMessenger 和 Navigator 实例，并统一使用 mounted 属性来确保 BuildContext 的安全使用，从而提高了 AcceptInvitationDialog 和 DeleteFamilyDialog 的健壮性。此外，还修正了 LoadingIndicator 和 QrCodeGenerator 中不正确的 const 关键字使用，以符合 Flutter 的最佳实践，并减少了代码中的分析器警告。

Highlights

• 上下文安全改进: 在 AcceptInvitationDialog 和 DeleteFamilyDialog 中，在异步操作前捕获 ScaffoldMessenger 和 Navigator 实例，以避免在 BuildContext 不再有效时使用它。
• mounted 检查统一: 将 context.mounted 检查统一为使用 mounted 属性，以确保组件在操作期间仍然挂载。
• const 关键字清理: 移除了 LoadingIndicator 和 QrCodeGenerator 中不正确的 const 关键字使用，这些 const 关键字应用于包含非常量表达式的 widget。
• 代码精简: 移除了 AcceptInvitationDialog 中未使用的 snackbar_utils 导入和 currentUser 变量。
• Provider 刷新优化: 在 DeleteFamilyDialog 中，将 ref.refresh 调用改为 final _ = ref.refresh，以明确其副作用并避免潜在的 lint 警告。

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[gemini-code-assist]

Code Review

This pull request effectively cleans up BuildContext usage by capturing navigator and messenger instances before async gaps, and also removes several invalid const keywords, which improves code correctness and adheres to best practices. The changes are well-executed. I have a couple of suggestions to further enhance the code's consistency and performance.

[gemini-code-assist]

While this is safe because of the mounted check, to be more consistent with the goal of this PR (capturing context-dependent objects before async gaps), you could define messenger before the try block. This would allow you to reuse it here in the catch block, avoiding another call to ScaffoldMessenger.of(context) and making the code cleaner.

Example:

// In _acceptInvitation() method, before the try block
final messenger = ScaffoldMessenger.of(context);
final navigator = Navigator.of(context);

try {
  // ... async operations
} catch (e) {
  if (mounted) {
    messenger.showSnackBar(
      SnackBar(
        content: Text('接受邀请失败: ${e.toString()}'),
        backgroundColor: Colors.red,
      ),
    );
  }
}
// ...

[gemini-code-assist]

This SizedBox can be a const constructor. Using const where possible is a Flutter best practice for performance optimization, as it helps avoid unnecessary widget rebuilds. Since this PR is focused on const cleanup, it would be good to ensure we are using const where it is valid.

Suggested change

	SizedBox(height: 16),
	const SizedBox(height: 16),