// Displays a Material dialog above the current contents of the app, with
/// Material entrance and exit animations, modal barrier color, and modal
/// barrier behavior (dialog is dismissible with a tap on the barrier).
///
/// This function takes a `builder` which typically builds a [Dialog] widget.
/// Content below the dialog is dimmed with a [ModalBarrier]. The widget
/// returned by the `builder` does not share a context with the location that
/// [showDialog] is originally called from. Use a [StatefulBuilder] or a
/// custom [StatefulWidget] if the dialog needs to update dynamically.
///

• 1局部更新dialog外套一层StatefulBuilder
• 2自定义dialog StatefulWidget
• 3强制build Element element=context as Element;
  element.markNeedsBuild();