我不确定它是否适用于您的情况,但在我的情况下(通过单击视图增加/减少房间中的项目数量)删除观察者并检查是否有活跃的观察者让我完成这项工作:
LiveData<MenuItem> menuitem = mViewModel.getMenuItemById(menuid);
menuitem.observe(this, (MenuItem menuItemRoom) ->{
menuitem.removeObservers(this);
if(menuitem.hasObservers())return;
// Do your single job here
});
});
2019 年 3 月 20 日更新:
现在我更喜欢这个:来自 Google Samples 中 MutableLiveData 的 EventWraper 类
/**
* Used as a wrapper for data that is exposed via a LiveData that represents an event.
*/
public class Event<T> {
private T mContent;
private boolean hasBeenHandled = false;
public Event( T content) {
if (content == null) {
throw new IllegalArgumentException("null values in Event are not allowed.");
}
mContent = content;
}
@Nullable
public T getContentIfNotHandled() {
if (hasBeenHandled) {
return null;
} else {
hasBeenHandled = true;
return mContent;
}
}
public boolean hasBeenHandled() {
return hasBeenHandled;
}
}
在视图模型中:
/** expose Save LiveData Event */
public void newSaveEvent() {
saveEvent.setValue(new Event<>(true));
}
private final MutableLiveData<Event<Boolean>> saveEvent = new MutableLiveData<>();
LiveData<Event<Boolean>> onSaveEvent() {
return saveEvent;
}
在活动/片段中
mViewModel
.onSaveEvent()
.observe(
getViewLifecycleOwner(),
booleanEvent -> {
if (booleanEvent != null)
final Boolean shouldSave = booleanEvent.getContentIfNotHandled();
if (shouldSave != null && shouldSave) saveData();
}
});