《Android编程权威指南》第二版 第五章 挑战练习

5.5挑战练习

GeoQuiz应用有一些漏洞，从易到难，以下为待解决的三个漏洞：

1.用户作弊后，可以旋转CheatActivity来清除作弊痕迹。

2.作弊返回后，用户可以旋转QuizActivity来消除mIsCheater变量值。

3.用户可以不断单击NEXT按钮，跳到偷看过答案的问题，从而使作弊记录丢失。

首选需要在CheatActivity里重写onSaveInstanceState(Bundle saveInstanceState)方法

@Override
public void onSaveInstanceState(Bundle saveInstanceState){
super.onSaveInstanceState(saveInstanceState);
Log.d(TAGG,"onSaveInstanceState");
saveInstanceState.putBoolean(DO,mWasCheat);
}

在这之前创建记录一个作弊痕迹的静态变量和两个标签常量

public static boolean mWasCheat = false;

private static final String TAGG = "CheatActivity";

private static final String DO = "Cheat?";

之后取出saveInstanceState中的值

if (savedInstanceState != null){
mWasCheat = savedInstanceState.getBoolean(DO,false);
}

为了在作弊之后一直显示答案使用以下判断

if (mWasCheat){
if (mAnswerIsTrue){
mAnswerTextView.setText(R.string.true_button);
}else {
mAnswerTextView.setText(R.string.false_button);
}
}

现在开始修改QuizActivity

首先将之前的mIsCheater删除，并将使用的部分替换为CheatActivity.mWasCheat

修改重写的onSaveInstanceState()中的代码

@Override
public void onSaveInstanceState(Bundle saveInstanceState){
super.onSaveInstanceState(saveInstanceState);
Log.d(TAG,"onSaveInstanceState");
saveInstanceState.putInt(KEY_INDEX,mCurrentIndex);
saveInstanceState.putBoolean(WAS_CHEAT,CheatActivity.mWasCheat);
}

取出如下

if(savedInstanceState != null){
mCurrentIndex = savedInstanceState.getInt(KEY_INDEX,0);
CheatActivity.mWasCheat = savedInstanceState.getBoolean(WAS_CHEAT,false);
}

现在还剩最后一部：重写onDestory()方法，使得应用销毁时将mWasCheat初始化

@Override
public void onDestroy(){
super.onDestroy();
CheatActivity.mWasCheat = false;
Log.d(TAG,"onDestroy() called");
}

贴上全部代码：

package com.example.fkxx.geoquiz;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;
import android.widget.Toast;

public class QuizActivity extends AppCompatActivity {

private Button mTrueButton;
private Button mFalseButton;
private Button mCheatButton;
private ImageButton mNextButton;
private ImageButton mPrivButton;
private TextView mQuestionTextView;
private static final String TAG = "QuizActivity";
private static final String KEY_INDEX = "index";
private static final String WAS_CHEAT = "cheat";
private static final int REQUEST_CODE_CHEAT = 0;

private Question[] mQuestionBank = new Question[]{
new Question(R.string.question_oceans,true),
new Question(R.string.question_mideast,false),
new Question(R.string.question_asia,false),
new Question(R.string.question_americas,true),
new Question(R.string.question_africa,true),
};

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 (CheatActivity.mWasCheat){
messageResId = R.string.judgment_toast;
}
else {
if (userPressedTrue == answerIsTrue){
messageResId = R.string.correct_toast;
}else {
messageResId = R.string.incorrect_toast;
}}
Toast.makeText(this,messageResId,Toast.LENGTH_SHORT).show();
}

private int mCurrentIndex = 0;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.d(TAG,"onCreate(Bundle) called");
setContentView(R.layout.activity_quiz);

mTrueButton = (Button)findViewById(R.id.true_button);
mFalseButton = (Button)findViewById(R.id.false_button);
mNextButton = (ImageButton) findViewById(R.id.next_button);
mPrivButton = (ImageButton) findViewById(R.id.priv_button);
mCheatButton = (Button)findViewById(R.id.cheat_button);
mQuestionTextView = (TextView)findViewById(R.id.question_text_view);
mCheatButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//start cheatActivity
boolean answerIsTrue = mQuestionBank[mCurrentIndex].isAnswerTrue();
//                Intent i = new Intent(QuizActivity.this,CheatActivity.class);
Intent i = CheatActivity.newIntent(QuizActivity.this,answerIsTrue);
//                startActivity(i);
startActivityForResult(i,REQUEST_CODE_CHEAT);
}
});

mTrueButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//                Toast.makeText(QuizActivity.this,R.string.correct_toast,Toast.LENGTH_SHORT).show();
checkAnswer(true);
}
});
mFalseButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
//            Toast.makeText(QuizActivity.this,R.string.incorrect_toast,Toast.LENGTH_SHORT).show();
checkAnswer(false);
}
});
mNextButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {

mCurrentIndex = (mCurrentIndex + 1)%mQuestionBank.length;
//                int question = mQuestionBank[mCurrentIndex].getTextResId();
//                mQuestionTextView.setText(question);
updateQuestion();
}
});
mPrivButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (mCurrentIndex<1){
mCurrentIndex+=mQuestionBank.length;
}
mCurrentIndex = (mCurrentIndex - 1)%mQuestionBank.length;
updateQuestion();
}
});
if(savedInstanceState != null){
mCurrentIndex = savedInstanceState.getInt(KEY_INDEX,0);
CheatActivity.mWasCheat = savedInstanceState.getBoolean(WAS_CHEAT,false);
}

updateQuestion();
}
@Override
public void onSaveInstanceState(Bundle saveInstanceState){
super.onSaveInstanceState(saveInstanceState);
Log.d(TAG,"onSaveInstanceState");
saveInstanceState.putInt(KEY_INDEX,mCurrentIndex);
saveInstanceState.putBoolean(WAS_CHEAT,CheatActivity.mWasCheat);
}
@Override
protected void onActivityResult(int requestCode,int resultCode,Intent data){
if(resultCode != Activity.RESULT_OK){
return;
}
if (requestCode == REQUEST_CODE_CHEAT){
if (data == null){
return;
}
Log.d(TAG,"onActivityResult");
CheatActivity.mWasCheat = CheatActivity.wasAnswerShown(data);
}
}

@Override
public void onStart(){
super.onStart();
Log.d(TAG,"onStart() called");
}
@Override
public void onPause(){
super.onPause();
Log.d(TAG,"onPause() called");
}
@Override
public void onResume(){
super.onResume();
Log.d(TAG,"onSResume() called");
}
@Override
public void onStop(){
super.onStop();
Log.d(TAG,"onStop() called");
}
@Override
public void onDestroy(){
super.onDestroy();
CheatActivity.mWasCheat = false;
Log.d(TAG,"onDestroy() called");
}
}

package com.example.fkxx.geoquiz;

import android.content.Context;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class CheatActivity extends AppCompatActivity {

private boolean mAnswerIsTrue;

private TextView mAnswerTextView;

private Button mShowAnswer;

public static boolean mWasCheat = false;

private static final String TAGG = "CheatActivity";

private static final String DO = "Cheat?";

private static final String EXTRA_ANSWER_IS_TRUE ="com.example.fkxx.geoquiz.answer_is_true";

private static final String EXTRA_ANSWER_SHOWN = "com.example.fkxx.geoquiz.answer_shown";

public static Intent newIntent(Context packageContent,boolean answerIsTrue){
Intent i = new Intent(packageContent,CheatActivity.class);
i.putExtra(EXTRA_ANSWER_IS_TRUE,answerIsTrue);
return i;
}
public static boolean wasAnswerShown(Intent result){
mWasCheat = result.getBooleanExtra(EXTRA_ANSWER_SHOWN,false);
return result.getBooleanExtra(EXTRA_ANSWER_SHOWN,false);

}
@Override
public void onSaveInstanceState(Bundle saveInstanceState){
super.onSaveInstanceState(saveInstanceState);
Log.d(TAGG,"onSaveInstanceState");
saveInstanceState.putBoolean(DO,mWasCheat);
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_cheat);

mAnswerIsTrue = getIntent().getBooleanExtra(EXTRA_ANSWER_IS_TRUE,false);

mAnswerTextView = (TextView)findViewById(R.id.answerTextView);

mShowAnswer = (Button)findViewById(R.id.showAnswerButton);

mShowAnswer.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
if (mAnswerIsTrue){
mAnswerTextView.setText(R.string.true_button);
}else {
mAnswerTextView.setText(R.string.false_button);
}
mWasCheat = true;
setAnswerShownResult(true);
}

});if (savedInstanceState != null){
mWasCheat = savedInstanceState.getBoolean(DO,false);
}
if (mWasCheat){
if (mAnswerIsTrue){
mAnswerTextView.setText(R.string.true_button);
}else {
mAnswerTextView.setText(R.string.false_button);
}
}

}
private void setAnswerShownResult(boolean isAnswerShown){
Intent data = new Intent();
data.putExtra(EXTRA_ANSWER_SHOWN,isAnswerShown);
setResult(RESULT_OK,data);
}
}

因为博主才学疏浅导致整个处理方式比较粗糙，还望谅解。