就像标题所示，当我按下按钮更改活动时，我的应用程序崩溃了。它在eclipse中显示没有错误并且最初打开但在按下按钮时关闭。最初应用程序根本不会打开，但我在onClick()内设置允许它打开的变量。
清单
<application
android:allowBackup="true"
android:icon="@drawable/globe"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.geoquizlab1solution.QuizActivity"
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.SportsQuiz"/>
</application>
第一个活动的类 ActivityQuiz.java ：
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;
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;
SharedPreferences app_preferences =
PreferenceManager.getDefaultSharedPreferences(this);
if (userPressedTrue == answerIsTrue) {
messageResId = R.string.correct_toast;
counter++;
}
else {
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) {
Intent intent = new Intent(this, MusicQuiz.java);
}
});*/
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;
}
}
SportsQuiz.java：
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;
public class SportsQuiz 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;
Intent intent1 = getIntent();
Intent intent = new Intent(this, SportsQuiz.class);
private TrueFalse[] mQuestionBank = new TrueFalse[] {
new TrueFalse(R.string.question_baseball, true),
new TrueFalse(R.string.question_football, false),
new TrueFalse(R.string.question_basketball, false),
new TrueFalse(R.string.question_hockey, true),
new TrueFalse(R.string.question_soccer, 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;
SharedPreferences app_preferences =
PreferenceManager.getDefaultSharedPreferences(this);
if (userPressedTrue == answerIsTrue) {
messageResId = R.string.correct_toast;
counter++;
}
else {
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();
}
/** Called when the activity is first created. */
@Override
public 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) {
startActivity(intent1);
}
});
/* mMusicButton = (Button)findViewById(R.id.music_button);
mMusicButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(this, MusicQuiz.java);
}
}); */
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;
}
}
这是日志：
04-04 20:48:42.600: E/AndroidRuntime(25939): FATAL EXCEPTION: main
04-04 20:48:42.600: E/AndroidRuntime(25939): Process: com.example.geoquizlab1solution, PID: 25939
04-04 20:48:42.600: E/AndroidRuntime(25939): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.geoquizlab1solution/com.example.geoquizlab1solution.SportsQuiz}: java.lang.NullPointerException
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2124)
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2257)
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.app.ActivityThread.access$800(ActivityThread.java:139)
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.os.Handler.dispatchMessage(Handler.java:102)
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.os.Looper.loop(Looper.java:136)
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.app.ActivityThread.main(ActivityThread.java:5097)
04-04 20:48:42.600: E/AndroidRuntime(25939): at java.lang.reflect.Method.invokeNative(Native Method)
04-04 20:48:42.600: E/AndroidRuntime(25939): at java.lang.reflect.Method.invoke(Method.java:515)
04-04 20:48:42.600: E/AndroidRuntime(25939): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
04-04 20:48:42.600: E/AndroidRuntime(25939): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
04-04 20:48:42.600: E/AndroidRuntime(25939): at dalvik.system.NativeStart.main(Native Method)
04-04 20:48:42.600: E/AndroidRuntime(25939): Caused by: java.lang.NullPointerException
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.content.ContextWrapper.getPackageName(ContextWrapper.java:135)
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.content.ComponentName.<init>(ComponentName.java:77)
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.content.Intent.<init>(Intent.java:3823)
04-04 20:48:42.600: E/AndroidRuntime(25939): at com.example.geoquizlab1solution.SportsQuiz.<init>(SportsQuiz.java:28)
04-04 20:48:42.600: E/AndroidRuntime(25939): at java.lang.Class.newInstanceImpl(Native Method)
04-04 20:48:42.600: E/AndroidRuntime(25939): at java.lang.Class.newInstance(Class.java:1208)
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.app.Instrumentation.newActivity(Instrumentation.java:1084)
04-04 20:48:42.600: E/AndroidRuntime(25939): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2115)
04-04 20:48:42.600: E/AndroidRuntime(25939): ... 11 more
答案 0 :(得分：0)
你无法指定一个你定义你的意图的对象
所以把这一行放在你的活动生命周期方法中，比如onCreate或其他任何一个，
只需在Oncreate方法
中写下这一行intent = new Intent（this，SportsQuiz.class）; intent1 = getIntent（）;