我想在flutter中显示对话框而不是使用底部导航栏的功能。我该如何实现？

@override
      Widget build(BuildContext context) {
      Widget child = Container();
      switch(_selectedIndex) {
        case 0:
          child = function_1();
          print("done");
          break;

        case 1:
          child = function_1();
          break;
      }

当我使用ShowDialog方法时，它说：

The following assertion was thrown building ServerGrid(dirty; state: _ServerGridState#59211289()):
I/flutter (14351): setState() or markNeedsBuild() called during build.
I/flutter (14351): This Overlay widget cannot be marked as needing to build because the framework is already in the
I/flutter (14351): process of building widgets. A widget can be marked as needing to be built during the build phase
I/flutter (14351): only if one of its ancestors is currently building. This exception is allowed because the framework
I/flutter (14351): builds parent widgets before children, which means a dirty descendant will always be built.
I/flutter (14351): Otherwise, the framework might not visit this widget during this build phase.