使用 TAB键 不能移动焦点

[sywxf]

════════ Exception caught by services library ══════════════════════════════════
Tried to get the bounds of a focus node that didn't have its context set yet.
The context needs to be set before trying to evaluate traversal policies. Setting the context is typically done with the attach method.
'package:flutter/src/widgets/focus_manager.dart':
Failed assertion: line 748 pos 9: 'context != null'