SaveInstanceState

1. 保存与读取当前状态，MainActivity.java

public class MainActivity extends AppCompatActivity {
    private String TAG = "MyLog";
    TextView textView;
    Button button;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = findViewById(R.id.textView);
        button = findViewById(R.id.button2);
        if (savedInstanceState != null) {
            String s = savedInstanceState.getString("KEY", "");
            Log.i(TAG, "onSaveInstanceState:" + s);
            textView.setText(s);
        }
        button.setOnClickListener(view -> textView.setText("This is a message"));
    }

    @Override
    protected void onSaveInstanceState(@NonNull Bundle outState) {
        super.onSaveInstanceState(outState);
        Log.i(TAG, "onSaveInstanceState:");
        outState.putString("KEY", textView.getText().toString());
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i(TAG, "onDestroy:");
    }
}