android - 我们应该在哪里更新 MVVM 中的模型

Question

我正在学习 MVVM。我正在阅读示例代码 https://codelabs.developers.google.com/codelabs/android-room-with-a-view关于 MVVM。有一个 Book 实体，它已从如下 Activity 更新:

Book book = new Book();
book.setName(x);

但我认为我们不应该在 View 层中有模型实例，我们应该在 ViewModel 中执行此操作，而不是在 View 中。类似于 View 中的以下代码:

MyViewModel viewModel = ViewModelProviders.of(this).get(MyViewModel.class);
viewModel.setBookName(x);

我的问题是我们可以在 View 中实例化一个实体吗？这样做的正确方法是什么？

Answer 1

您应该只更新 View 模型中的模型类..

为 Activity 创建接口(interface) IContract.java

 public interface IContract {

    interface View 
    {
        public void displayModelData();

    }

    interface ViewModel 
    {
        public Book setModelData();
        public Book getModelData();
    }
}

• Then implement View interface in Activity class and View Model Interface in ViewModel class..

• Now create an reference ViewModel object in Activity class.

• where we can pass the data from ViewModel to View using that object

Activity 课 MainActivity.java

public class MainActivity implements IContract.View {
    private IContract.ViewModel viewModel; //create a instance for ViewModel object

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        this.viewModel = new MainActivityViewModel(getApplicationContext());// object initialisation


        @overide
        public void displayModelData()
        {
            viewModel.setModelData(); // update model class
            Book obj = viewModel.getModelData();// this will get book object from viewModel class.
            Toast(obj.Name);
        }

    }
}

MainActivityViewModel.java

  public class MainActivityViewModelimplements IContract.ViewModel

{
    Context context;
    Book book;

    public void MainActivityViewModel (Context context)
    {
        this.context = context;
    }


    @Override
    public void setModelData ()
    {
        book = new Book(); // update model class.
        book.setName(x);
    }

    @Override
    public Book getModelData ()
    {
        return book; //return the object to the view
    }

}