Activity onSaveInstanceState in the absence of view IDs

Question

The default implementation of Activity#onSaveInstanceState says:

The default implementation takes care of most of the UI per-instance state for you by calling onSaveInstanceState() on each view in the hierarchy that has an id

The Android Data binding guide, and this video - slide 9 suggests that we no longer need View IDs when using Data Binding. My question is: How does the absence of View IDs affect state save/restore?

Arguably, when using data-binding one shouldn't depend on the default mechanism to save/restore state, instead depending on the ViewModel bound to the layout to have the most up-to-date state, but I'm still curious to know about the implications.

Answer 1

您不需要ID并不意味着您永远不应该使用ID。这是为了更新您的视图。还有许多其他情况，其中id类似于RelativeLayout中的规则。

因此，如果状态恢复对您的用例很重要（例如，您的模型需要一段时间才能恢复），请务必使用ID并禁用绑定，直到您的数据准备就绪。

Answer 2

  

我的问题是：缺少视图ID会如何影响状态保存/恢复？

要直接回答您的问题，缺少视图ID会阻止onSaveInstanceState恢复该视图。对于没有ID的视图，Android的文档仍然适用。

任何没有ID的视图仍会被重新创建，但它们的状态不会恢复。

我刚刚在一个简单的应用程序中对此进行了测试，没有ID的视图没有恢复其状态。