android activity状态保存

    private String SAVE_INSTANCE_TAG = "ATWAL";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_cal);

        if (savedInstanceState != null) {
            String s = savedInstanceState.getString(SAVE_INSTANCE_TAG);
        }
    }

    //系统在回收当前Activity之前会调用，Back & Home 不会调用此方法
    @Override
    public void onSaveInstanceState(Bundle outState, PersistableBundle outPersistentState) {
        if (outState != null) {
            outState.putString(SAVE_INSTANCE_TAG, "hello atwal");
        }
        super.onSaveInstanceState(outState, outPersistentState);
    }

    @Override
    protected void onResume() {
        super.onResume();
        String s = this.getPreferences(MODE_PRIVATE).getString(SAVE_INSTANCE_TAG, "");
    }

    @Override
    protected void onPause() {
        super.onPause();
        this.getPreferences(MODE_PRIVATE).edit().putString(SAVE_INSTANCE_TAG, "after pause");
    }