Android编程权威指南-第5章：挑战练习
QuizActivity.java
package com.onevol.app;
import java.util.ArrayList;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import com.example.geoquiz.R;
public class QuizActivity extends Activity {
private static final String KEY_INDEX = "index";
//新建一个常量作为Bundle的键，将mCurrectIndex变量作为Bundle的值。
//用于在翻转设备后，保持题目号码不变。
private static final String KEY_CHEAT = "cheater";
//作为值mIsCheater的键。用于保持是否查看过答案的Boolean值不变。
private static final String KEY_NUMBER = "number";
//作为值list的键。用于保持保存看过答案的题目号的容器不变。
private Button mTureButton;
private Button mFalseButton;
private Button mPrevButton;
private Button mNextButton;
private Button mCheatButton;
private TextView mQuestionTextView;
private TrueFalse[] mQuestionBank = new TrueFalse[] {
new TrueFalse(R.string.question_africa, false),
new TrueFalse(R.string.question_americas, true),
new TrueFalse(R.string.question_asia, true),
new TrueFalse(R.string.question_mideast, false),
new TrueFalse(R.string.question_oceans, true),
};
private int mCurrectIndex = 0;//题目号码
private boolean mIsCheater;//是否看过答案
private int mClickedNumber;//看过答案的题目号码
private ArrayList list = new ArrayList();//保存看过答案的题目号码的容器
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// TODO Auto-generated method stub
super.onActivityResult(requestCode, resultCode, data);
if(data == null){
return;
}
mIsCheater = data.getBooleanExtra("answer_shown", false);//接受返回的是否看过答案
mClickedNumber = data.getIntExtra("clicked_number", 0);//接受看过答案的题目号码
if((Integer)mClickedNumber != null){
list.add(mClickedNumber);//将看过答案的题目号码添加到容器里
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_quiz);
mTureButton = (Button) findViewById(R.id.ture_button);
mFalseButton = (Button) findViewById(R.id.false_button);
mPrevButton = (Button) findViewById(R.id.prev_button);
mNextButton = (Button) findViewById(R.id.next_button);
mCheatButton = (Button) findViewById(R.id.cheat_button);
mQuestionTextView = (TextView) findViewById(R.id.question_text);
if(savedInstanceState != null){//在onCreate()方法中检查储存的Bundle信息。在UpdateQuestion()方法前检查。
mCurrectIndex = savedInstanceState.getInt(KEY_INDEX);
mIsCheater = savedInstanceState.getBoolean(KEY_CHEAT);
list = savedInstanceState.getIntegerArrayList(KEY_NUMBER);
//保持屏幕翻转前的数据不变
}
updateQuestion();
mTureButton.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
// Toast.makeText(QuizActivity.this, "Incorrect", Toast.LENGTH_SHORT).show();
checkAnswer(true);
}
});
mFalseButton.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
// Toast.makeText(QuizActivity.this, "Correct", Toast.LENGTH_SHORT).show();
checkAnswer(false);
}
});
mPrevButton.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
mIsCheater = false;//初始化是否看过答案的值
if(mCurrectIndex == 0){
int question = mQuestionBank[mQuestionBank.length -1].getQuestion();
mQuestionTextView.setText(question);
mCurrectIndex = 4;
} else{
mCurrectIndex = (mCurrectIndex -1);
updateQuestion();
}
}
});
mNextButton.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
mCurrectIndex = (mCurrectIndex + 1) % mQuestionBank.length;
mIsCheater = false;//初始化是否看过答案的值
updateQuestion();
}
});
mCheatButton.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent intent = new Intent(QuizActivity.this, CheatActivity.class);
boolean answerIsTrue = mQuestionBank[mCurrectIndex].isTrueQuestion();
intent.putExtra("answer", answerIsTrue);//将获取的答案传到intent中
intent.putExtra("number", mCurrectIndex);//将现在的题号传到intent中
// startActivity(intent);
startActivityForResult(intent, 0);
}
});
mQuestionTextView.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
mCurrectIndex = (mCurrectIndex + 1) % mQuestionBank.length;
mIsCheater = false;//初始化是否看过答案的值
updateQuestion();
}
});
}
private void updateQuestion() {
int question = mQuestionBank[mCurrectIndex].getQuestion();
mQuestionTextView.setText(question);
}
private void checkAnswer (boolean userPressedTrue){
boolean answerIsTrue = mQuestionBank[mCurrectIndex].isTrueQuestion();
if(mIsCheater || list.contains(mCurrectIndex)){//检查是否看过是看过的答案或现在的题号是否被包含在容器中
Toast.makeText(this, "cheating is wrong.", Toast.LENGTH_SHORT).show();
} else{
if(userPressedTrue == answerIsTrue){
Toast.makeText(this, "Correct", Toast.LENGTH_SHORT).show();
} else{
Toast.makeText(this, "Incorrect", Toast.LENGTH_SHORT).show();
}
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// TODO Auto-generated method stub
return super.onCreateOptionsMenu(menu);
}
@Override
protected void onSaveInstanceState(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onSaveInstanceState(savedInstanceState);
savedInstanceState.putInt(KEY_INDEX, mCurrectIndex);
//将mCurrectIndex(题号)储存到Bundle中。
savedInstanceState.putBoolean(KEY_CHEAT, mIsCheater);
//将是否看过答案的值储存
savedInstanceState.putIntegerArrayList(KEY_NUMBER, list);
//将保存看过答案的题目号的容器储存
}
} 出现的错误java.lang.NullPointerException
在private ArrayList 这一行没有实例化ArrayList。改为private ArrayList
CheatActivity.java
package com.onevol.app;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import com.example.geoquiz.R;
public class CheatActivity extends Activity {
private static final String KEY_CLICK = "click";
private boolean mAnswerIsTrue;
private boolean mIsClick;
private TextView mAnswerTextView;
private Button mShowAnswer;
private int mNumber;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_cheat);
mAnswerIsTrue = getIntent().getBooleanExtra("answer", false);//得到答案
mNumber = getIntent().getIntExtra("number", 0);//得到题号
mAnswerTextView = (TextView) findViewById(R.id.answerTextView);
mShowAnswer = (Button) findViewById(R.id.showAnswerButton);
if(savedInstanceState != null){//保持屏幕翻转后 查看答案的按钮是否被点击过的值不变
mIsClick = savedInstanceState.getBoolean(KEY_CLICK);
if(mAnswerIsTrue){//并显示答案
mAnswerTextView.setText(R.string.true_button);
} else {
mAnswerTextView.setText(R.string.false_button);
}
}
mIsClick=false;//初始化查看答案的按钮是否被点击过
setAnswerShownResult(mIsClick);//发送没看过答案
mShowAnswer.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
if(mAnswerIsTrue){//并显示答案
mAnswerTextView.setText(R.string.true_button);
} else {
mAnswerTextView.setText(R.string.false_button);
}
mIsClick = true;
setAnswerShownResult(mIsClick);//发送看过答案
}
});
}
private void setAnswerShownResult(boolean isAnswerShown){
Intent intent = new Intent();
intent.putExtra("answer_shown", isAnswerShown);//传出是否看过答案的值
if(isAnswerShown){//如果看过答案，就将该题号传出
intent.putExtra("clicked_number", mNumber);
}
setResult(RESULT_OK, intent);
}
@Override
protected void onSaveInstanceState(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onSaveInstanceState(savedInstanceState);
savedInstanceState.putBoolean(KEY_CLICK, mIsClick);
//保存查看答案的按钮是否被点击过的值
}
}activity_quiz.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical" >
<TextView
android:id="@+id/question_text"
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/ture_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/cheat_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/cheat_button"/>
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="horizontal">
<Button
android:id="@+id/prev_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/prev_button"
android:drawableLeft="@drawable/arrow_left"
android:drawablePadding="4dp"/>
<Button
android:id="@+id/next_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/next_button"
android:drawableRight="@drawable/arrow_right"
android:drawablePadding="4dp"/>
LinearLayout>
LinearLayout>activity_cheat.xml
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:gravity="center" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="24dp"
android:text="@string/warning_text"/>
<TextView
android:id="@+id/answerTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="24dp" />
<Button
android:id="@+id/showAnswerButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/show_answer_button"/>
LinearLayout>land\activity_quiz.xml
"http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
id="@+id/question_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:padding="24dp"
/>
"wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_vertical|center_horizontal"
android:orientation="horizontal">