Android JetPack组件之ViewModel状态的保存(程序在后台被系统杀死数据也存活)

public class DataBindingActivity extends AppCompatActivity {
    private ViewModelWithDataBinding viewModelWithDataBinding;
    //当我们将layout文件转换为DataBinding的形式，Android studio会帮我们创建这样一个类
    //这个类的名称就是layout文件的名字 加上Binding
    private ActivityDataBindingBinding binding;
    public static final String KEY = "data_key";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //创建这个对象后，layout文件里面的标签，就会成为ActivityDataBindingBinding这个类的成员，可以直接访问
        binding = DataBindingUtil.setContentView(this, R.layout.activity_data_binding);
        viewModelWithLiveData = new ViewModelProvider(this).get(ViewModelWithLiveData.class);
        if (savedInstanceState != null) {
            viewModelWithDataBinding.getNumber().setValue(savedInstanceState.getInt(KEY));
        }
        binding.setData(viewModelWithDataBinding);
        binding.setLifecycleOwner(this);
    }
    @Override
    public void onSaveInstanceState(@NonNull Bundle outState, @NonNull PersistableBundle outPersistentState) {
        super.onSaveInstanceState(outState, outPersistentState);
        outState.putInt(KEY, viewModelWithDataBinding.getNumber().getValue());
    }
}

implementation "androidx.lifecycle:lifecycle-viewmodel-savedstate:2.2.0"

public class ViewModelWithDataBinding extends ViewModel {
    private SavedStateHandle handle;
    //新增的一个构造函数
    public ViewModelWithDataBinding(SavedStateHandle handle) {
        this.handle = handle;
    }
    public MutableLiveData getNumber() {
        if (!handle.contains(DataBindingActivity.KEY)) {
            handle.set(DataBindingActivity.KEY, 0);
        }
        return handle.getLiveData(DataBindingActivity.KEY);
    }
    public void add() {
        getNumber().setValue(getNumber().getValue() + 1);
    }
}

public class DataBindingActivity extends AppCompatActivity {
    private ViewModelWithDataBinding viewModelWithDataBinding;
    //当我们将layout文件转换为DataBinding的形式，Android studio会帮我们创建这样一个类
    //这个类的名称就是layout文件的名字 加上Binding
    private ActivityDataBindingBinding binding;
    public static final String KEY = "data_key";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //创建这个对象后，layout文件里面的标签，就会成为ActivityDataBindingBinding这个类的成员，可以直接访问
        binding = DataBindingUtil.setContentView(this, R.layout.activity_data_binding);
        viewModelWithDataBinding = new ViewModelProvider(this,new SavedStateViewModelFactory(getApplication(),this)).get(ViewModelWithDataBinding.class);
        binding.setData(viewModelWithDataBinding);
        binding.setLifecycleOwner(this);
    }
}