override fun onSaveInstanceState(outState: Bundle) {
        super.onSaveInstanceState(outState)
        val tempData="Something you just typed"
        outState.putString("data_key",tempData)
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_first)
        if(savedInstanceState!=null){
            val tempData = savedInstanceState.getString("data_key")
            tempData?.let { Log.d("tag", it) }
        }
}

package com.example.viewmodeldemo;
import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.ViewModelProvider;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
    private MyViewModel mMyViewModel;
    private TextView textView;
    private Button mButton1;
    private Button mButton2;
    private final String TAG="MainActivityTest";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.d(TAG, "onCreate: ");
        //創(chuàng)建一個(gè)ViewModel對(duì)象
        mMyViewModel = new ViewModelProvider(this, new ViewModelProvider.NewInstanceFactory()).get(MyViewModel.class);
        textView=findViewById(R.id.textView);
        //ViewModel會(huì)保存數(shù)據(jù)，當(dāng)你重新創(chuàng)建的時(shí)候會(huì)加載顯示出來
        textView.setText(String.valueOf(mMyViewModel.number));
        mButton1=findViewById(R.id.button1);
        mButton2=findViewById(R.id.button2);
        mButton1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                mMyViewModel.number++;
                textView.setText(String.valueOf(mMyViewModel.number));
            }
        });
        mButton2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                mMyViewModel.number+=2;
                textView.setText(String.valueOf(mMyViewModel.number));
            }
        });
    }
    @Override
    protected void onStart() {
        super.onStart();
        Log.d(TAG, "onStart: ");
    }
    @Override
    protected void onStop() {
        super.onStop();
        Log.d(TAG, "onStop: ");
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy: ");
    }
    @Override
    protected void onPause() {
        super.onPause();
        Log.d(TAG, "onPause: ");
    }
    @Override
    protected void onResume() {
        super.onResume();
        Log.d(TAG, "onResume: ");
    }
}

package com.example.viewmodeldemo;
import androidx.lifecycle.ViewModel;
//這里的ViewModel可以看作全局變量倉(cāng)庫(kù)
public class MyViewModel extends ViewModel {
    public int number=0;
}