如果你升级项目后报错参考
 The android.arch Architecture Components packages are no longer maintained. They have been superseded by the corresponding androidx.* packages. See androidx.lifecycle.Transformations instead.
以前使用方法

import androidx.lifecycle.Transformations

 LiveData userLiveData = ...;
 LiveData userName = Transformations.map(userLiveData, user -> {
      return user.firstName + " " + user.lastName
 });
 
 MutableLiveData userIdLiveData = ...;
 LiveData userLiveData = Transformations.switchMap(userIdLiveData, id ->
     repository.getUserById(id));

 void setUserId(String userId) {
      this.userIdLiveData.setValue(userId);
 }

最新使用方法

import androidx.lifecycle.switchMap
import androidx.lifecycle.map

val userLD : LiveData<User> = ...;
val userFullNameLD: LiveData<String> = userLD.map { user -> user.firstName + user.lastName }


class UserViewModel: AndroidViewModel {
    val nameQueryLiveData : MutableLiveData<String> = ...

    fun usersWithNameLiveData(): LiveData<List<String>> = nameQueryLiveData.switchMap {
        name -> myDataSource.usersWithNameLiveData(name)
    }

    fun setNameQuery(val name: String) {
        this.nameQueryLiveData.value = name;
    }
}