Android编程权威指南第三版挑战练习三

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挑战练习三 完整代码 ->Link

 

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挑战练习-题目-1: 禁止一题多答

       用户答完某道题,就禁掉那道题对应的按钮,防止用户一题多答。

 

参考解决办法:

step 1:加入数据,与get、set方法(Question.java)

   

    private boolean mAnswered;
    
    public Question(int textResId, boolean answerTrue) {
       ...
    }

    public boolean isAnswered() {
        return mAnswered;
    }

    public void setAnswered(boolean answered) {
        mAnswered = answered;
    }

解释:加入了mAnswered属性,用来标记是否完成回答。

step 2:设置函数,在QuizActivity类内,checkAnswer()后。(QuizActivity)

 

    //封装一个检查是否回答过问题的函数,以便调用
    private void checkIfAnswered(){
        boolean answerIsAnswered = mQuestionBank[mCurrentIndex].isAnswered();
        if (answerIsAnswered == true) {
            //如果题目被回答,则按键设置不可按下
            mTrueButton.setEnabled(false);
            mFalseButton.setEnabled(false);

        } else {
            //如果题目没有被回答,则按键设置可按下
            mTrueButton.setEnabled(true);
            mFalseButton.setEnabled(true);
        }
    }

 

解释:回到主Acitivity,实现检测按钮是否按下的函数,以便调用。

step 3:在下面两个地方调用checkIfAnswered(),并加入mQuestionBank.......(QuizActivity.java)

 

    private void updateQuestion() {
        ...
        mQuestionTextView.setText(question);
        checkIfAnswered();
    }
    private void checkAnswer(boolean userPressedTrue) {
       ... else {
            messageResId = R.string.incorrect_toast;
        }
        mQuestionBank[mCurrentIndex].setAnswered(true);
        checkIfAnswered();
      Toast.makeText(this, messageResId, Toast.LENGTH_SHORT)
                .show();
    }

解释:在每一次页面刷新时&点击true或false按钮之后,调用刚刚写的CheckIfAnswered函数,刷新两个按钮的状态。

加上一句mQuestionBank[mCurrentIndex].setAnswered(true)是设置刚刚新增的属性,即记录下问题是否被回答。

step 4:存储数据(QuizActivity.java)

 

 
 @Override
    public void onSaveInstanceState(Bundle savedInstanceState) {

        super.onSaveInstanceState(savedInstanceState);
        Log.i(TAG, "onSaveInstanceState");
        savedInstanceState.putInt(KEY_INDEX, mCurrentIndex);
        boolean answerIsAnswered[] = new boolean[mQuestionBank.length];
        for(int i = 0; i < mQuestionBank.length;i++)
        {
            answerIsAnswered[i] = mQuestionBank[i].isAnswered();

        }
        savedInstanceState.putBooleanArray(KEY_ANSWERED, answerIsAnswered);

    }

解释:将是否回答的数据存入数组,然后放到Bundle中。KEY_ANSWERED此时可能有红色波浪线,完成下一步,加入KEY_ANSWERED即可。

step 5 : 取出数据

 

private static final String KEY_INDEX = "index";
    private static final String KEY_ANSWERED = "answered";
    ...
        if (savedInstanceState != null) {

            mCurrentIndex = savedInstanceState.getInt(KEY_INDEX, 0);
            boolean answerIsAnswered[] = savedInstanceState.getBooleanArray(KEY_ANSWERED);
            for(int i = 0; i < mQuestionBank.length;i++)
            {
                mQuestionBank[i].setAnswered(answerIsAnswered[i]) ;
            }

        }

解释:加上标志KEY_ANSWERED,保存所有Answered状态,

 

至此,完成了第一道题目。

Android编程权威指南第三版挑战练习三_第1张图片

相关资料:

函数:void putBooleanArray(String key, boolean[] value)
解释:Inserts a boolean array value into the mapping of this Bundle, replacing any existing value for the given key.
 

挑战练习-题目-2:评分

       用户答完全部题后,显示一个toast消息,给出百分比形式的评分。

 

参考解决办法:(基于上一题的参考答案,不然会出bug)

step 1:QuizActivity.java数据域加入全局变量(QuizActivity.java)

 

private int userAnsweredCorrect = 0;
...
private static final String KEY_CORRECT = "correct";

解释:设置变量userAnswerCorrect记录答对的题目数量。用 公式“答对的题 / 全部题目 = 答对率” 即可计算评分

step 2:记录答对次数

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

        int messageResId = 0;
        if (userPressedTrue == answerIsTrue) {
            messageResId = R.string.correct_toast;
            //如果答对则记录答对次数
            userAnsweredCorrect++;
        } else {
            messageResId = R.string.incorrect_toast;
        }
        mQuestionBank[mCurrentIndex].setAnswered(true);
        checkIfAnswered();
        Toast.makeText(this, messageResId, Toast.LENGTH_SHORT)
                .show();
    }

step 3:增加显示百分比函数(QuizActivity.java)

 
    private void showRecored(){
        boolean allAnsnswered = true;
        String message = null;
        double correctMark = 0;//百分比形式的评分,正确率
        int correctAnswerNum = 0;//答对的题目数量
        for(int i = 0; i < mQuestionBank.length; i++){
            if(mQuestionBank[i].isAnswered() == false) {
                allAnsnswered = false;
                break;
            }
        }
        if(allAnsnswered == true){
            correctMark = (double)userAnsweredCorrect/mQuestionBank.length;
            //保留后两位
            correctMark = (double)((int)(correctMark * 10000)/100.0);
            message = "正确率" + String.valueOf(correctMark) + "%";
            Toast.makeText(this, message, Toast.LENGTH_SHORT).show();
        }
    }
解释:allAnswered表示是否全部答对,for循环用于检索是否还有没有回答的题目,如果都回答了,allAnswered为true,计算答对率并输出。

step 4:三个按钮的回调函数里调用(QuizActivity.java)

   mTrueButton = (Button) findViewById(R.id.true_button);
        mTrueButton.setOnClickListener(new View.OnClickListener() {
           ...
                showRecored();
            }
        });
        mFalseButton = (Button) findViewById(R.id.false_button);
        mFalseButton.setOnClickListener(new View.OnClickListener() {
            ...
                showRecored();
            }
        });

        mNextButton = (Button) findViewById(R.id.next_button);
        mNextButton.setOnClickListener(new View.OnClickListener() {
           ...
                showRecored();
            }
        });
解释:目的是要在按下按钮时,检查是否答完全部题目,如果回答完了,输出评分。所以三个按钮的回调函数里面都有放置显示函数。

step 5:同理,保存数据KEY_CORRECT(QuizActivity.java)

 

    @Override
    public void onSaveInstanceState(Bundle savedInstanceState) {
        ...
        savedInstanceState.putInt(KEY_CORRECT, userAnsweredCorrect);
    }
解释:同上,保存userAnsweredCorrect即答对的题目数量,到bundle中。

step 6:取出数据(QuizActivity.java)

 

    @Override
    protected void onCreate(Bundle savedInstanceState) {
      ...
            userAnsweredCorrect = savedInstanceState.getInt(KEY_CORRECT);
        }
解释:取出数据

 

至此,完成第三章的挑战练习

Android编程权威指南第三版挑战练习三_第2张图片

 

 

 

 

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