所以我创建了一个小问答游戏的应用程序，我有3个活动，每个活动都有自己的问题类型。最初我将地理区域作为启动屏幕，但是当我尝试将启动屏幕更改为＆＃34;主页时＃34;该应用程序无法启动。 Eclipse显示0个错误。
新的HomeScreen代码：
package com.example.geoquizlab1solution;
import android.app.Activity;
import android.content.Intent;
//import android.content.SharedPreferences;
import android.os.Bundle;
//import android.preference.PreferenceManager;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
//import android.widget.ImageButton;
import android.widget.TextView;
//import android.widget.Toast;
import android.media.MediaPlayer;
public class HomeScreen extends Activity {
private TextView mWelcome;
private Button mSportsButton;
private Button mGeoButton;
private Button mMusicButton;
final MediaPlayer mp = MediaPlayer.create(this, R.raw.welcome);
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.home_page);
mWelcome = (TextView)findViewById(R.id.welcome_text);
( (View) mWelcome) .setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
mp.start();
}
});
mGeoButton = (Button)findViewById(R.id.geo_button);
mGeoButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
final Intent intent1 = new Intent(HomeScreen.this, QuizActivity.class);
if (intent1 != null) {
startActivity(intent1);
}
}
});
mSportsButton = (Button)findViewById(R.id.sports_button);
mSportsButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
final Intent intent1 = new Intent(HomeScreen.this, SportsQuiz.class);
if (intent1 != null) {
startActivity(intent1);
}
}
});
mMusicButton = (Button)findViewById(R.id.music_button);
mMusicButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
final Intent intent1 = new Intent(HomeScreen.this, MusicQuiz.class);
if (intent1 != null) {
startActivity(intent1);
}
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_quiz, menu);
return true;
}
}
旧的启动画面代码：
package com.example.geoquizlab1solution;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;
import android.widget.Toast;
import android.media.MediaPlayer;
public class QuizActivity extends Activity {
private Button mTrueButton;
private Button mFalseButton;
private ImageButton mNextButton;
private ImageButton mPreviousButton;
private TextView mQuestionTextView;
private Button mResetButton;
private Button mSportsButton;
private Button mGeoButton;
private Button mMusicButton;
private int counter = 0;
private TrueFalse[] mQuestionBank = new TrueFalse[] {
new TrueFalse(R.string.question_oceans, true),
new TrueFalse(R.string.question_mideast, false),
new TrueFalse(R.string.question_africa, false),
new TrueFalse(R.string.question_americas, true),
new TrueFalse(R.string.question_asia, true)
};
private int mCurrentIndex=0;
private void updateQuestion(){
int question = mQuestionBank[mCurrentIndex].getQuestion();
mQuestionTextView.setText(question);
}
private void checkAnswer(boolean userPressedTrue) {
boolean answerIsTrue = mQuestionBank[mCurrentIndex].isTrueQuestion();
int messageResId = 0;
final MediaPlayer mp = MediaPlayer.create(this, R.raw.ding);
final MediaPlayer mp1 = MediaPlayer.create(this, R.raw.wrong);
SharedPreferences app_preferences =
PreferenceManager.getDefaultSharedPreferences(this);
if (userPressedTrue == answerIsTrue) {
mp.start();
messageResId = R.string.correct_toast;
counter++;
if (counter % 5 == 0) {
final MediaPlayer mp2 = MediaPlayer.create(this, R.raw.applause);
mp2.start();
}
}
else {
mp1.start();
messageResId = R.string.incorrect_toast;
}
SharedPreferences.Editor editor = app_preferences.edit();
editor.putInt("count", counter);
Toast.makeText(this, messageResId, Toast.LENGTH_SHORT).show();
Toast.makeText(this,"Score:" + counter, Toast.LENGTH_SHORT).show();
editor.commit();
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_quiz);
mGeoButton = (Button)findViewById(R.id.geo_button);
mGeoButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
counter = 0;
Toast.makeText(getApplicationContext(), "Score: 0",
Toast.LENGTH_SHORT).show();
mCurrentIndex = 0;
updateQuestion();
}
});
mSportsButton = (Button)findViewById(R.id.sports_button);
mSportsButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
final Intent intent1 = new Intent(QuizActivity.this, SportsQuiz.class);
if (intent1 != null) {
startActivity(intent1);
}
}
});
mMusicButton = (Button)findViewById(R.id.music_button);
mMusicButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
final Intent intent1 = new Intent(QuizActivity.this, MusicQuiz.class);
if (intent1 != null) {
startActivity(intent1);
}
}
});
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);
}
});
mQuestionTextView = (TextView)findViewById(R.id.question_text_view);
((View) mQuestionTextView) .setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mCurrentIndex = (mCurrentIndex + 1) % mQuestionBank.length;
updateQuestion();
}
});
updateQuestion();
mPreviousButton = (ImageButton)findViewById(R.id.previous_button);
((View) mPreviousButton) .setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (mCurrentIndex != 0) {
mCurrentIndex = (mCurrentIndex - 1) % mQuestionBank.length;
updateQuestion();
}
else {
mCurrentIndex = (mCurrentIndex + 4) % mQuestionBank.length;
}
}
});
updateQuestion();
mNextButton = (ImageButton)findViewById(R.id.next_button);
((View) mNextButton).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
mCurrentIndex = (mCurrentIndex + 1) % mQuestionBank.length;
updateQuestion();
}
});
updateQuestion();
mResetButton = (Button)findViewById(R.id.reset_button);
((View) mResetButton).setOnClickListener(new View.OnClickListener () {
@Override
public void onClick(View v) {
counter = 0;
Toast.makeText(getApplicationContext(), "Score: 0",
Toast.LENGTH_SHORT).show();
mCurrentIndex = 0;
updateQuestion();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.activity_quiz, menu);
return true;
}
}
AndroidManifest文件：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.geoquizlab1solution"
android:versionCode="2"
android:versionName="1.1"
xmlns:tools="http://schemas.android.com/tools" tools:ignore="OldTargetApi">
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="23"
android:maxSdkVersion="23"/>
<application
android:allowBackup="true"
android:icon="@drawable/quiz"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.geoquizlab1solution.HomeScreen"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity android:screenOrientation="unspecified" android:name="com.example.geoquizlab1solution.QuizActivity"/>
<activity android:screenOrientation="unspecified" android:name="com.example.geoquizlab1solution.SportsQuiz"/>
<activity android:screenOrientation="unspecified" android:name="com.example.geoquizlab1solution.MusicQuiz"/>
</application>
</manifest>
新主屏幕布局文件：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:background="@drawable/spotlight">
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:textAlignment="gravity"
android:gravity="center"
android:textStyle="italic"
android:id="@+id/welcome_text"
android:textColor="#5E5E5E"
android:background="@drawable/welcomeview"/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:layout_weight="6">
<Button
android:id="@+id/geo_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/geo_button"
android:textColor="#2ADB20"
android:background="#275393"
android:layout_margin="25dp"/>
<Button
android:id="@+id/sports_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/sports_button"
android:textColor="#FFFFFF"
android:background="#ED1515"
android:layout_margin="25dp"/>
<Button
android:id="@+id/music_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/music_button"
android:textColor="#FFD700"
android:background="#544F4F"
android:layout_margin="25dp"/>
</LinearLayout>
日志：
04-05 15:46:29.861: E/AndroidRuntime(22191): FATAL EXCEPTION: main
04-05 15:46:29.861: E/AndroidRuntime(22191): Process: com.example.geoquizlab1solution, PID: 22191
04-05 15:46:29.861: E/AndroidRuntime(22191): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.geoquizlab1solution/com.example.geoquizlab1solution.HomeScreen}: java.lang.NullPointerException
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2124)
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2257)
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.app.ActivityThread.access$800(ActivityThread.java:139)
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.os.Handler.dispatchMessage(Handler.java:102)
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.os.Looper.loop(Looper.java:136)
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.app.ActivityThread.main(ActivityThread.java:5097)
04-05 15:46:29.861: E/AndroidRuntime(22191): at java.lang.reflect.Method.invokeNative(Native Method)
04-05 15:46:29.861: E/AndroidRuntime(22191): at java.lang.reflect.Method.invoke(Method.java:515)
04-05 15:46:29.861: E/AndroidRuntime(22191): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
04-05 15:46:29.861: E/AndroidRuntime(22191): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
04-05 15:46:29.861: E/AndroidRuntime(22191): at dalvik.system.NativeStart.main(Native Method)
04-05 15:46:29.861: E/AndroidRuntime(22191): Caused by: java.lang.NullPointerException
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.content.ContextWrapper.getResources(ContextWrapper.java:89)
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:78)
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.media.MediaPlayer.create(MediaPlayer.java:844)
04-05 15:46:29.861: E/AndroidRuntime(22191): at com.example.geoquizlab1solution.HomeScreen.<init>(HomeScreen.java:22)
04-05 15:46:29.861: E/AndroidRuntime(22191): at java.lang.Class.newInstanceImpl(Native Method)
04-05 15:46:29.861: E/AndroidRuntime(22191): at java.lang.Class.newInstance(Class.java:1208)
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.app.Instrumentation.newActivity(Instrumentation.java:1084)
04-05 15:46:29.861: E/AndroidRuntime(22191): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2115)
04-05 15:46:29.861: E/AndroidRuntime(22191): ... 11 more
04-05 15:46:32.298: D/PhoneStatusBar(1186): StatusBarWindow onTouchListener.onTouch
答案 0 :(得分：0)
删除＆＃39; final MediaPlayer mp = MediaPlayer.create(this, R.raw.welcome);＆＃39;并将其嵌入onCrete()方法中，在创建活动之前设置值会导致此错误