Question

我的应用程序onSaveInstanceState实现。我已经成功实现了我的onSaveInstanceState，但它没有在方向更改时维护当前的问题。以下是我的MainActivity。我一直在页面上关注BigNerdRanchGuide这本书。我不明白为什么它不起作用。

感谢。

    public class MainActivity extends AppCompatActivity {

        public static final String TAG  = "QuizActivity";
        public static final String KEY_INDEX = "index";

        private TextView mTextView;
        private Button mTrueButton, mFalseButton;
        private ImageButton mNext, mPrev;

        private Question[] mQuestionBank = new Question[]{
                new Question((R.string.pacific_ocean), true),
                new Question((R.string.syria_europe), false),
                new Question((R.string.canada_na), true),
                new Question((R.string.africa_country), false),
                new Question((R.string.china_continent), false)
        };

        private int mCurrentIndex = 0;

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

            Log.d(TAG, "OnCreate(Bundle) called");

            if(savedInstanceState != null){
                mCurrentIndex = savedInstanceState.getInt(KEY_INDEX, 0);
            }

            mTextView = (TextView)findViewById(R.id.question);
            int question = mQuestionBank[mCurrentIndex].getTextResId();
            mTextView.setText(question);
...

        @Override
        public void onSaveInstanceState(Bundle outState) {
            super.onSaveInstanceState(outState);
            Log.i(TAG, "onSaveInstanceState");
            outState.putInt(KEY_INDEX, mCurrentIndex);
        }



        private void updateQuestion() {
            mCurrentIndex = (mCurrentIndex + 1) % mQuestionBank.length;
            int question = mQuestionBank[mCurrentIndex].getTextResId();
            mTextView.setText(question);
        }

        private void lastQuestion(){

            if (mCurrentIndex > 0){
                mCurrentIndex = (mCurrentIndex - 1) % mQuestionBank.length;
                int question = mQuestionBank[mCurrentIndex].getTextResId();
                mTextView.setText(question);
            }else{
                Toast.makeText(this, "You're at the last question", Toast.LENGTH_SHORT).show();
                return;
            }
        }

        private void checkAnswer(boolean userPressedTrue){
            boolean answerIsTrue = mQuestionBank[mCurrentIndex].isAnswerTrue();

            int messageResId = 0;

            if(userPressedTrue == answerIsTrue){
                messageResId = R.string.correct;
            }else{
                messageResId = R.string.incorrect;
            }
            Toast.makeText(this, messageResId, Toast.LENGTH_SHORT).show();
        }
    }

Answer 1

我们假设currentIndex=2。旋转屏幕并重新创建活动时，currentIndex将具有保存值。这里的问题是，您在创建活动时将问题设置为2次：首先在这里

int question = mQuestionBank[mCurrentIndex].getTextResId();
mTextView.setText(question);

并且onCreate结束时第二次（通过调用updateQuestion()不再可见）。因此，值2将最终成为3，从而导致这种奇怪的行为。一个可能的解决方案是从上面删除第一段代码，从当前索引中减去一个，并确保将当前索引的值设置为-1（您可能已经注意到显示的第一个问题实际上是第二个数组中的一个。）

OnSaveInstanceState不保存实例

1 个答案: