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