屏幕改变方向时会调用什么？ 更改方向后，我的应用程序正在重新启动

Question

I have built an app that is a simple question and answer game. A Question is displayed and you can select true or false, and then a toast appears to tell you if you got the question correct. You can then press a button to move to the next question. The problem is that when you rotate the screen (change the screens orientation) the app goes back to the first question displayed. What gets called to make this happen? I have three classes. The first is the MainActivity which launches the quiz layout. The next is a Question class. The last is the QuizActivity Class. Here is the code:

MainActivity:

package com.example.geoquiz;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

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

Question Class:

package com.example.geoquiz;

public class Question {
    private int mTextResId;
    private boolean mAnswerTrue;
    public Question(int textResId, boolean answerTrue) {
        mTextResId = textResId;
        mAnswerTrue = answerTrue;
    }
    public int getTextResId() {
        return mTextResId;
    }
    public void setTextResId(int textResId) {
        mTextResId = textResId;
    }
    public boolean isAnswerTrue() {
        return mAnswerTrue;
    }
    public void setAnswerTrue(boolean answerTrue) {
        mAnswerTrue = answerTrue;
    }
}

QuizActivity Class:

package com.example.geoquiz;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

public class QuizActivity extends AppCompatActivity {
    private Button mTrueButton;
    private Button mFalseButton;
    private Button mNextButton;
    private TextView mQuestionTextView;
    private Question[] mQuestionBank = new Question[] {
            new Question(R.string.question_australia, true),
            new Question(R.string.question_oceans, true),
            new Question(R.string.question_mideast, false),
            new Question(R.string.question_africa, false),
            new Question(R.string.question_americas, true),
            new Question(R.string.question_asia, true),
    };
    private int mCurrentIndex = 0;
// ...
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_quiz);
    mQuestionTextView = (TextView)    findViewById(R.id.question_text_view);
    mTrueButton = (Button) findViewById(R.id.true_button);
    mTrueButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) { checkAnswer(true); }
    });
    mFalseButton = (Button) findViewById(R.id.false_button);
    mFalseButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) { checkAnswer(false); }
    });
    mNextButton = (Button) findViewById(R.id.next_button);
    mNextButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mCurrentIndex = (mCurrentIndex + 1) % mQuestionBank.length;
            updateQuestion();
        }
    });
    updateQuestion();
}
    private void updateQuestion() {
        int question = mQuestionBank[mCurrentIndex].getTextResId();
        mQuestionTextView.setText(question);
    }
    private void checkAnswer(boolean userPressedTrue) {
        boolean answerIsTrue = mQuestionBank[mCurrentIndex].isAnswerTrue();
        int messageResId = 0;
        if (userPressedTrue == answerIsTrue) {
            messageResId = R.string.correct_toast;
        } else {
            messageResId = R.string.incorrect_toast;
        }
        Toast.makeText(this, messageResId, Toast.LENGTH_SHORT).show();
    }

} // to close the entire class

I believe the code to update the question begins in the QuizActivity class. I think the issue is that the counter for which question to be displayed is being set back to 0, but I do not know where to set a breakpoint to check this. Whenever I set a breakpoint none of the UI is updated and I can therefore not test this.

I also have the XML file if you want to test this for yourself:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="wrap_content"
    android:layout_width="wrap_content"
    android:orientation="vertical">
<TextView
android:id="@+id/question_text_view"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="24dp" />
    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/true_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/true_button" />

        <Button
            android:id="@+id/false_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="@string/false_button" />

    </LinearLayout>
    <Button
    android:id="@+id/next_button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/next_button" />
</LinearLayout>

Answer 1

The problem is that when you rotate the screen (change the screens orientation) the app goes back to the first question displayed. What gets called to make this happen?

Your activity is destroyed and recreated as part of a configuration change . Consider using a ViewModel to hold your activity's state and be able to retain it across configuration changes.

Answer 2

您可以使用ViewModel或重写onSaveInstanceState（Bundle savedInstanceState）并将要更改的应用程序状态值写入到Bundle参数中，例如当前的问题编号，它将被传入onCreate（）和onRestoreInstanceState（）中，然后从中提取价值。