英文:
How to save UI state observed in ViewModel when rotating device?
问题
我有一个显示地点详情的用户界面(UI)，其中包括一些文本编辑框(EditTexts)和一个来自于 这个 ExpandableRecyclerView 库 的适配器(adapter)。
在 onCreate 中，当我的 ViewModel 观察到地点的变化时，我会更新 UI。我会在 onSaveInstanceState 中保存适配器，然后在 onRestoreInstanceState 中进行恢复。
然而，一旦我旋转设备，旧的 UI 状态就会显示出来。例如，我在文本编辑框中输入一些文本并展开适配器，但是在我旋转设备后，旧的文本和折叠的适配器会出现。我认为这是因为在 onChanged 被调用之前适配器为 null，因此在 onRestoreInstanceState 中跳过了我的适配器方法，然后在 onChanged 中 EditTexts 被重新更新为旧文本。
我该如何保存 UI 的状态？
完整的代码可以在这里找到。
onCreate:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detail);
viewModel = new ViewModelProvider(this).get(PlaceViewModel.class);
Intent intent = getIntent();
if (intent.hasExtra(EXTRA_PLACE_ID)) {
String id = intent.getStringExtra(EXTRA_PLACE_ID);
viewModel.getPlaceById(id).observe(this, new Observer<PlaceModel>() {
@Override
public void onChanged(PlaceModel placeModel) {
// 如果地点未被删除，placeModel 将不为 null
if (placeModel != null) {
// 在这里更新 UI
}
}
});
}
}
onSaveInstanceState 和 onRestoreInstanceState:
/* 要保存适配器的展开和折叠状态，
必须显式地调用适配器的 onSaveInstanceState() 和 onRestoreInstanceState() 方法 */
@Override
protected void onSaveInstanceState(@NonNull Bundle outState) {
super.onSaveInstanceState(outState);
if (adapter != null) {
adapter.onSaveInstanceState(outState);
}
}
@Override
protected void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
if (adapter != null) {
adapter.onRestoreInstanceState(savedInstanceState);
}
}
英文:
I have UI displaying details of a place, including some EditTexts and an adapter from this ExpandableRecyclerView library.
The UI is updated in onCreate when my ViewModel observes a change to the place. I save the adapter in onSaveInstanceState and restore it in onRestoreInstanceState.
However once I rotate my device, the old UI state is displayed. For example, I enter some text to the EditText and expand my adapter, but after I rotate my device the old text and collapsed adapter appears. I think this is because adapter is null until onChanged is called, so my adapter method in onRestoreInstanceState is skipped, and EditTexts are re-updated to old text in onChanged.
How do I save the state of my UI?
Full code can be found here.
onCreate:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_detail);
viewModel = new ViewModelProvider(this).get(PlaceViewModel.class);
Intent intent = getIntent();
if (intent.hasExtra(EXTRA_PLACE_ID)) {
String id = intent.getStringExtra(EXTRA_PLACE_ID);
viewModel.getPlaceById(id).observe(this, new Observer<PlaceModel>() {
@Override
public void onChanged(PlaceModel placeModel) {
// placeModel will be null if place is deleted
if (placeModel != null) {
// update UI here
}
}
});
}
}
onSaveInstanceState and onRestoreInstanceState:
/* To save the expand and collapse state of the adapter,
you have to explicitly call through to the adapter's
onSaveInstanceState() and onRestoreInstanceState() in the calling Activity */
@Override
protected void onSaveInstanceState(@NonNull Bundle outState) {
super.onSaveInstanceState(outState);
if (adapter != null) {
adapter.onSaveInstanceState(outState);
}
}
@Override
protected void onRestoreInstanceState(@NonNull Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
if (adapter != null) {
adapter.onRestoreInstanceState(savedInstanceState);
}
}
答案1
得分: 0
一个解决方法就是检查 savedInstanceState 是否为 null，如果为 null，则不设置 EditText 的文本并恢复适配器状态。
但是我没有仔细阅读 ViewModel 文档： "ViewModel 类旨在以考虑生命周期的方式存储和管理与 UI 相关的数据。ViewModel 类允许数据在配置更改（如屏幕旋转）后继续存在。"
我之前在问为什么 ViewModel 在旋转后会保存我的旧 UI 相关数据...尽管这实际上正是它应该做的...这是我的错误。
英文:
One solution is just check if savedInstanceState is null, if it is don't set text of EditTexts and restore adapter state.
But I didn't carefully read the ViewModel documentation: "The ViewModel class is designed to store and manage UI-related data in a lifecycle conscious way. The ViewModel class allows data to survive configuration changes such as screen rotations."
I was asking why ViewModel is saving my old UI-related data after rotation...even though that's exactly what it's supposed to do...my mistake.
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