继承BaseObservable的ViewModel与Android自带ViewModel类的区别是什么？

Great question—this is such a common sticking point when diving into MVVM on Android, because both terms get thrown around under the "ViewModel" umbrella but they serve totally different purposes. Let’s break this down clearly:

1. Core Purpose & Responsibility #

These two classes solve entirely separate problems:

• Custom classes extending BaseObservable
  This is essentially an observable data holder. Its sole job is to let the UI know when its data changes. By using @Bindable annotations and notifyPropertyChanged(), you can link its fields directly to your UI via DataBinding, so updates to the data automatically reflect in the views. It doesn’t handle lifecycle or data persistence across configuration changes—it’s just a way to make your data "observable."

  Example:

  public class User extends BaseObservable {
      private String name;
  
      @Bindable
      public String getName() {
          return name;
      }
  
      public void setName(String name) {
          this.name = name;
          notifyPropertyChanged(BR.name); // Triggers UI update
      }
  }
  

• Android’s official ViewModel class
  This is part of Android’s Architecture Components, and its core job is to hold and manage UI-related data across configuration changes (like screen rotations). It’s lifecycle-aware—when your Activity/Fragment is recreated due to a config change, the ViewModel is retained, so your data doesn’t get lost. It doesn’t handle data observation on its own (you’ll pair it with LiveData or BaseObservable for that), but it’s the central place to put your UI-related business logic (like loading data, handling user actions).

  Example:

  public class ProfileViewModel extends ViewModel {
      private final MutableLiveData<User> userLiveData = new MutableLiveData<>();
  
      public LiveData<User> getUserLiveData() {
          return userLiveData;
      }
  
      public void loadUserProfile() {
          // Simulate fetching data from a repository
          User fetchedUser = new User();
          fetchedUser.setName("Urvish");
          userLiveData.postValue(fetchedUser);
      }
  }
  

2. Lifecycle Awareness #

This is a critical distinction:

• BaseObservable classes have no lifecycle awareness. They live and die with whatever object creates them (like an Activity or ViewModel). If your Activity is destroyed (even for a config change), any BaseObservable instance tied to it will be garbage collected, and its data will be lost.
• ViewModel classes are managed by the system’s ViewModelStore. They survive configuration changes and are only destroyed when the host Activity/Fragment is permanently finished (like when the user presses back). The system calls onCleared() on the ViewModel when it’s time to clean up resources.

3. Typical Use Cases #

• Use BaseObservable when:
  You need a simple way to make a data class’s fields observable for DataBinding. It’s perfect for small, self-contained data models where you want direct UI updates without wrapping everything in LiveData.

• Use Android’s ViewModel when:
  You need to retain data across config changes, or you want a dedicated place to handle UI-related logic (data loading, user interaction handling). It’s the "glue" between your Model (data sources) and View (UI elements).

4. How They Work Together #

Most of the time, these two classes complement each other, not compete. You’ll often see a ViewModel holding instances of BaseObservable objects, or using LiveData to wrap observable data. For example:

public class ProfileViewModel extends ViewModel {
    private final User user = new User(); // Extends BaseObservable

    public User getUser() {
        return user;
    }

    public void updateUserName(String newName) {
        user.setName(newName); // Triggers UI update via BaseObservable
    }
}

Here, the ViewModel retains the User object across rotations, and the BaseObservable handles notifying the UI when the name changes.

内容的提问来源于stack exchange，提问作者Urvish rana