ViewModel 概览

ViewModel概览https://developer.android.google.cn/topic/libraries/architecture/viewmodel
ViewModel Class is to pay attention to the life cycle of way to store and manage relevant data interface.ViewModel 类让数据可在发生屏幕旋转等配置更改后继续留存.
ViewModel的亮点：

This note mainly analyze the persistence of data is also：

ViewModel使用

添加依赖

    implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'

定义ViewModel

public class MyViewModel extends ViewModel {
    
    
    // There can be any variable
    public int number;

}

使用ViewModel

public class MainActivity extends AppCompatActivity {
    

    private MyViewModel myViewModel;
    private TextView mTextView;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myViewModel = new ViewModelProvider(this).get(MyViewModel.class);
        mTextView = findViewById(R.id.text);
        mTextView.setText(myViewModel.number + "");
    }


    public void onTextView(View view) {
    
        myViewModel.number = myViewModel.number + 1;
        mTextView.setText(myViewModel.number + "");
    }
}

运行上面代码以后,When user change configuration such as the screen,ViewModelSave data is not lost;

ViewModel原理分析

至于ViewModelOnline there are a lot of the cause of the data is stored in the content,说白了就是一句话,The above data are stored in public memory;
涉及到两个方法：

• onRetainNonConfigurationInstance() 是在Activity 销毁的时候 进行存储信息.

• getLastNonConfigurationInstance() 的作用是获取onRetainNonConfigurationInstance存储的信息.

当屏幕发生旋转的时候 ,会先调用 onRetainNonConfigurationInstance先将数据进行保存,然后再通过 getLastNonConfigurationInstance 将保存的数据获取到.
The inside of the specific code is no longer a list,有兴趣可以自己查看;