Jetpack-ViewModelSavedState

添加依赖

def lifecycle_version = "2.2.0"
    implementation "androidx.lifecycle:lifecycle-livedata-ktx:$lifecycle_version"
    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version"
    implementation "androidx.lifecycle:lifecycle-viewmodel-savedstate:$lifecycle_version"

activity_view_model_saved_state.xml

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto" >

    <data>
        <variable
            name="data"
            type="com.jsecode.qnsmw.SavedStateViewModel" />
    </data>
    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <Button
            android:id="@+id/button3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginStart="147dp"
            android:layout_marginTop="314dp"
            android:text="@string/btn_add"
            android:onClick="@{()->data.add()}"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="21dp"
            android:layout_height="19dp"
            android:layout_marginStart="180dp"
            android:layout_marginTop="128dp"
            android:text="@{data.number.toString()}"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

SavedStateViewModel.java

    private SavedStateHandle handle;

    public SavedStateViewModel(SavedStateHandle handle) {
        this.handle = handle;
    }

    public MutableLiveData<Integer> getNumber() {
        if (!handle.contains(ViewModelSavedStateActivity.KEY_NUMBER)) {
            handle.set(ViewModelSavedStateActivity.KEY_NUMBER, 0);
        }
        return this.handle.getLiveData(ViewModelSavedStateActivity.KEY_NUMBER);
    }

    public void add() {
        getNumber().setValue(getNumber().getValue() + 1);
    }
}

ViewModelSavedStateActivity.java

public class ViewModelSavedStateActivity extends AppCompatActivity {

    public static final String KEY_NUMBER = "number";
    ActivityViewModelSavedStateBinding binding;
    SavedStateViewModel viewModel;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.setContentView(this, R.layout.activity_view_model_saved_state);
        ViewModelProvider viewModelProvider = new ViewModelProvider(this,new SavedStateViewModelFactory(getApplication(),this));
        viewModel = viewModelProvider.get(SavedStateViewModel.class);

        binding.setData(viewModel);
        binding.setLifecycleOwner(this);
    }
}