AndroidViewModel

让MyViewModel继承自AndroidViewModel

这样可以使MyViewModel访问全局资源

MainActivity

package com.example.viewmodelshp;

import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.lifecycle.SavedStateViewModelFactory;
import androidx.lifecycle.ViewModelProvider;

import android.os.Bundle;

import com.example.viewmodelshp.databinding.ActivityMainBinding;

public class MainActivity extends AppCompatActivity {
    MyViewModel myViewModel;
    ActivityMainBinding binding;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        binding= DataBindingUtil.setContentView(this,R.layout.activity_main);
        myViewModel=new ViewModelProvider(this,new SavedStateViewModelFactory(getApplication(),this)).get(MyViewModel.class);
        binding.setData(myViewModel);
        binding.setLifecycleOwner(this);
    }

    @Override
    protected void onPause() {
        super.onPause();
        myViewModel.save();
    }
}

MyViewModel

package com.example.viewmodelshp;

import android.app.Application;
import android.content.Context;
import android.content.SharedPreferences;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.LiveData;
import androidx.lifecycle.SavedStateHandle;

@SuppressWarnings("ConstantConditions")
public class MyViewModel extends AndroidViewModel {
    private SavedStateHandle handle;
    private String key = getApplication().getResources().getString(R.string.data_key);
    private String shpname = getApplication().getResources().getString(R.string.shp_name);

    public MyViewModel(Application application, SavedStateHandle handle) {
        super(application);
        this.handle = handle;
        if (!handle.contains(key)) {
            load();
        }
    }

    public LiveData<Integer> getNumber() {
        return handle.getLiveData(key);
    }

    private void load() {
        SharedPreferences shp = getApplication().getSharedPreferences(shpname, Context.MODE_PRIVATE);
        int x = shp.getInt(key, 0);
        handle.set(key, x);
    }

    public void save() {
        SharedPreferences shp = getApplication().getSharedPreferences(shpname, Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = shp.edit();
        editor.putInt(key, getNumber().getValue());
        editor.apply();
    }

    public void add(int x) {
        handle.set(key, getNumber().getValue() + x);
        // save();
    }

}