在Android编程中，经常会有多个Activity之间、同Activity的旋转都要进行调用，数据传递的现象。如何理解Activity，确保正确的调用是每个Androider必须掌握的知识。

1：Activity旋转过程中通过Bundle实例进行数据读写，在onCreate(Bundle)读取、onSaveInstanceState(Bundle)写入。

例子：

protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_quiz);        //读取数据，并保存到类变量中        if (null != savedInstanceState) {            mCurrentIndex = savedInstanceState.getInt(KEY_INDEX);            mCheatersArray = savedInstanceState.getBooleanArray(USER_CHEAT_RECORD);        }        ***}protected void onSaveInstanceState(Bundle savedInstanceState) {        super.onSaveInstanceState(savedInstanceState);        //保存当前题目编号        savedInstanceState.putInt(KEY_INDEX, mCurrentIndex);        //保存用户作弊记录        savedInstanceState.putBooleanArray(USER_CHEAT_RECORD, mCheatersArray);            //保存两项数据，在onCreate方法中调用传递数据    }}

2：Activity之间的调用通过startActivity(Intent)只向子Activity传递数据，不会接收子Activity传回的数据；startActivityForResult(***)向子Activity传递数据，并通过onActivityResult(***)方法读取子Activity传回的数据。子Activity通过setResult(***)向父Activity传递数据。

//父Activity方法    //通过mCheatButton事件，创建子Activity实例，并传递数据    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        printLogInConsole(TAG, ONCREATE);        setContentView(R.layout.activity_quiz);        ***        mCheatButton = (Button) findViewById(R.id.cheat_button);        ***        mCheatButton.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                Intent i = new Intent(QuizActivity.this, CheatActivity.class);                boolean answerIsTrue = mQuestionBank[mCurrentIndex].isTrueQuestion();                //传入所选问题索引、标准答案                i.putExtra(CheatActivity.EXTRA_ANSWER_IS_TRUE, answerIsTrue);                i.putExtra(CheatActivity.EXTRA_ANSWER_INDEX, mCurrentIndex);                //仅向子Activity传递数据                //startActivity(i);                //向子Activity传递数据并获取返回数据                startActivityForResult(i, CheatActivity.CHEAT_REQUEST_CODE);            }        });        ***    }    //获取子Activity返回的数据    @Override    protected void onActivityResult(int requestCode, int resultCode, Intent data) {        //是否对应的Activity返回        if (CheatActivity.CHEAT_REQUEST_CODE != requestCode) {            return;        }        if (RESULT_OK != resultCode) {            return;        }        if (null == data) {            return;        }        mIsCheater = data.getBooleanExtra(CheatActivity.EXTRA_ANSWER_SHOWN, false);        mCurrentIndex = data.getIntExtra(CheatActivity.EXTRA_ANSWER_INDEX, 0);        //更新用户作弊信息        mCheatersArray[mCurrentIndex] = mIsCheater;    }    //子Activity    //子Activity通过setResutl向父Activity传递数据    private void setAnswerShownResult(boolean isAnswerShown) {        Intent data = new Intent();        data.putExtra(EXTRA_ANSWER_SHOWN, isAnswerShown);        data.putExtra(EXTRA_ANSWER_INDEX, mCurrentIndex);        setResult(RESULT_OK, data);    }