我正在编写一个小型时间表项目，并在从学校导入到家中后，我收到此错误。请记住，我已经四次检查我在我需要的每个地方都使用了getSupportActionBar（）。
04-03 10:54:02.561: E/AndroidRuntime(24473): FATAL EXCEPTION: main
04-03 10:54:02.561: E/AndroidRuntime(24473): Process: com.pipturner.timetable, PID: 24473
04-03 10:54:02.561: E/AndroidRuntime(24473): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.pipturner.timetable/com.pipturner.timetable.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null objectreference
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2314)
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2388)
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.app.ActivityThread.access$800(ActivityThread.java:148)
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1292)
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.os.Handler.dispatchMessage(Handler.java:102)
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.os.Looper.loop(Looper.java:135)
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.app.ActivityThread.main(ActivityThread.java:5312)
04-03 10:54:02.561: E/AndroidRuntime(24473): at java.lang.reflect.Method.invoke(Native Method)
04-03 10:54:02.561: E/AndroidRuntime(24473): at java.lang.reflect.Method.invoke(Method.java:372)
04-03 10:54:02.561: E/AndroidRuntime(24473): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
04-03 10:54:02.561: E/AndroidRuntime(24473): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
04-03 10:54:02.561: E/AndroidRuntime(24473): Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setDisplayHomeAsUpEnabled(boolean)' on a null object reference
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.support.v7.app.ActionBarImplICS.setDisplayHomeAsUpEnabled(ActionBarImplICS.java:179)
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.support.v7.app.ActionBarImplJB.setDisplayHomeAsUpEnabled(ActionBarImplJB.java:20)
04-03 10:54:02.561: E/AndroidRuntime(24473): at com.pipturner.timetable.NavigationDrawerFragment.setUp(NavigationDrawerFragment.java:146)
04-03 10:54:02.561: E/AndroidRuntime(24473): at com.pipturner.timetable.MainActivity.onCreate(MainActivity.java:76)
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.app.Activity.performCreate(Activity.java:5953)
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1128)
04-03 10:54:02.561: E/AndroidRuntime(24473): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2267)
04-03 10:54:02.561: E/AndroidRuntime(24473): ... 10 more
这是调用它的MainActivity
package com.pipturner.timetable;
import java.util.List;
import Database.DatabaseHelper;
import Database.MC_shomework;
import Database.MC_slesson;
import Database.MC_sschoolday;
import android.app.Activity;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.support.v4.widget.DrawerLayout;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends ActionBarActivity implements
NavigationDrawerFragment.NavigationDrawerCallbacks {
DatabaseHelper db;
OnClickListener homeworkOnClickListener =
new OnClickListener(){
@Override
public void onClick(View v) {
Class<?> homework = Input_shomework.class;
StartIntent(homework); //run the add a new homework screen
}
};
OnClickListener lessonOnClickListener =
new OnClickListener(){
@Override
public void onClick(View v) {
Class<?> lesson = Input_slesson.class;
StartIntent(lesson); //run the add a new homework screen
}
};
/**
* Fragment managing the behaviors, interactions and presentation of the
* navigation drawer.
*/
private NavigationDrawerFragment mNavigationDrawerFragment;
/**
* Used to store the last screen title. For use in
* {@link #restoreActionBar()}.
*/
private CharSequence mTitle;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mNavigationDrawerFragment = (NavigationDrawerFragment) getSupportFragmentManager()
.findFragmentById(R.id.navigation_drawer);
mTitle = getTitle();
// Set up the drawer.
mNavigationDrawerFragment.setUp(R.id.navigation_drawer,
(DrawerLayout) findViewById(R.id.drawer_layout));
createDataItems(); //adds lessons and days to the database
getUserSettings(); //gets the settings from the preference screen and stores them into the database
displayUserSettings(); //gets the settings that were stored in the database and displays them in a text field
displayUserHomeworks(); //gets and displays the homeworks
Button button = (Button) findViewById(R.id.homeworkbutton); //sets a button to the homework button
button.setOnClickListener(homeworkOnClickListener); //if the button is clicked, do the homeworkOnClickListener
// Button lessonbutton = (Button) findViewById(R.id.lessonbutton);
//lessonbutton.setOnClickListener(lessonOnClickListener);
}
private void createDataItems(){
db = new DatabaseHelper(getApplicationContext());
MC_sschoolday[] sday = new MC_sschoolday[8];
MC_slesson[] slesson = new MC_slesson[7];
sday[1] = new MC_sschoolday(1, "Monday", "n", 0); //creates a schoolday
sday[2] = new MC_sschoolday(2, "Tuesday", "n", 0);
sday[3] = new MC_sschoolday(3, "Wednesday", "n", 0);
sday[4] = new MC_sschoolday(4, "Thursday", "n", 0);
sday[5] = new MC_sschoolday(5, "Friday", "n", 0);
sday[6] = new MC_sschoolday(6, "Saturday", "n", 0);
sday[7] = new MC_sschoolday(7, "Sunday", "n", 0);
slesson[1] = new MC_slesson(1, "Maths", "21", "Mrs Anderson"); //creates a lesson
slesson[2] = new MC_slesson(2, "Maths", "14", "Mr Dhillow");
slesson[3] = new MC_slesson(3, "English", "2", "Mr Duck");
slesson[4] = new MC_slesson(4, "English", "3", "Mrs Brown");
slesson[5] = new MC_slesson(5, "Computing", "C1", "Mr King");
slesson[6] = new MC_slesson(6, "Computing", "C3", "Ms Brown");
if (db.getAllSSchoolDays().size()<7){
// Creating schooldays
// Inserting them in db
db.createSSchoolDay(sday[1]);
db.createSSchoolDay(sday[2]);
db.createSSchoolDay(sday[3]);
db.createSSchoolDay(sday[4]);
db.createSSchoolDay(sday[5]);
db.createSSchoolDay(sday[6]);
db.createSSchoolDay(sday[7]);
Log.v("Main Activity", "Added Schooldays");
}
if(db.getAllLessons().size()<6){
//inserts lessons into database
db.createSLesson(slesson[1]);
db.createSLesson(slesson[2]);
db.createSLesson(slesson[3]);
db.createSLesson(slesson[4]);
db.createSLesson(slesson[5]);
db.createSLesson(slesson[6]);
}
}
private void getUserSettings() {
boolean[] d = new boolean[7];
int[] dp = new int[7];
String[] dps = new String[7];
MC_sschoolday[] sday = new MC_sschoolday[8];
sday[1] = new MC_sschoolday(1, "Monday", "n", 0); //creates a schoolday
sday[2] = new MC_sschoolday(2, "Tuesday", "n", 0);
sday[3] = new MC_sschoolday(3, "Wednesday", "n", 0);
sday[4] = new MC_sschoolday(4, "Thursday", "n", 0);
sday[5] = new MC_sschoolday(5, "Friday", "n", 0);
sday[6] = new MC_sschoolday(6, "Saturday", "n", 0);
sday[7] = new MC_sschoolday(7, "Sunday", "n", 0);
SharedPreferences sharedPrefs = PreferenceManager
.getDefaultSharedPreferences(this);
d[0] =sharedPrefs.getBoolean("schooldays_monday", false);
dps[0]=sharedPrefs.getString("schooldays_monday_periods", "0");
d[1] =sharedPrefs.getBoolean("schooldays_tuesday", false);
dps[1]=sharedPrefs.getString("schooldays_tuesday_periods", "0");
d[2] =sharedPrefs.getBoolean("schooldays_wednesday", false);
dps[2]=sharedPrefs.getString("schooldays_wednesday_periods","0");
d[3] =sharedPrefs.getBoolean("schooldays_thursday", false);
dps[3]=sharedPrefs.getString("schooldays_thursday_periods", "0");
d[4] =sharedPrefs.getBoolean("schooldays_friday", false);
dps[4]=sharedPrefs.getString("schooldays_friday_periods", "0");
d[5] =sharedPrefs.getBoolean("schooldays_saturday", false);
dps[5]=sharedPrefs.getString("schooldays_saturday_periods", "0");
d[6] =sharedPrefs.getBoolean("schooldays_sunday", false);
dps[6]=sharedPrefs.getString("schooldays_sunday_periods", "0");
for(int i=0; i<7;i++){
dp[i] = Integer.parseInt(dps[i]);
Log.v("Days", "Parsed String to int " + i + " times(s)");
}
for(int i=0; i<7;i++){
if(d[i]){
sday[i+1].setUsed("y");
sday[i+1].setNo_of_lessons(dp[i]);
db.updatesSchoolDay(sday[i+1]);
}
}
db.closeDB();
}
private void displayUserSettings(){
String[] days = new String[7];
db = new DatabaseHelper(getApplicationContext());
MC_sschoolday[] sday = new MC_sschoolday[7];
List<MC_sschoolday> schoolday = db.getAllSSchoolDays();
for (int i =0; i< db.getAllSSchoolDays().size(); i++){
sday[i]=schoolday.get(i);
}
for(int i =0;i < 7; i++){
// if(sday[i].getUsed()=="y"){
days[i]=(sday[i].getschool_day()+": \n" +
" Number Of Lessons: "+sday[i].getNo_of_lessons()+"\n");
// }
}
TextView settingsTextView = (TextView) findViewById(R.id.lessons);
settingsTextView.setText(
days[0] +days[1] + days[2] + days[3] +days[4] +days[5] +days[6]
+ "\n NUMBER OF DAYS " +db.getAllSSchoolDays().size() + "\n NUMBER OF HOMEWORKS " + db.getAllHomework().size());
db.close();
}
public void displayUserHomeworks(){
db = new DatabaseHelper(getApplicationContext());
int homeworksize = db.getAllHomework().size();
MC_shomework[] shomework = new MC_shomework[homeworksize];
List<MC_shomework> homeworklist = db.getAllHomework();
String[] homeworkString = new String[homeworksize];
for (int i =0; i< homeworksize; i++){
shomework[i]=homeworklist.get(i);
}
for(int i =0;i < homeworksize; i++){
homeworkString[i]=("Lesson ID: " + shomework[i].getSlesson_ID()+": \n" +
" Duedate: "+shomework[i].getShomework_duedate()+"\n"+
" Details: "+shomework[i].getShomework_details()+"\n");
}
if(homeworksize>0){
TextView settingsTextView = (TextView) findViewById(R.id.homeworktext);
settingsTextView.setText(
homeworkString[0]
);
}
db.close();
}
@Override
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager
.beginTransaction()
.replace(R.id.container,
PlaceholderFragment.newInstance(position + 1)).commit();
}
public void onSectionAttached(int number) {
switch (number) {
case 1:
mTitle = getString(R.string.title_section1);
break;
case 2:
mTitle = getString(R.string.title_section2);
break;
case 3:
mTitle = getString(R.string.title_section3);
break;
}
}
public void restoreActionBar() {
ActionBar actionBar = getSupportActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
actionBar.setDisplayShowTitleEnabled(true);
actionBar.setTitle(mTitle);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
if (!mNavigationDrawerFragment.isDrawerOpen()) {
// Only show items in the action bar relevant to this screen
// if the drawer is not showing. Otherwise, let the drawer
// decide what to show in the action bar.
getMenuInflater().inflate(R.menu.main, menu);
restoreActionBar();
return true;
}
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
Class<?> settings= SettingsActivity.class;
StartIntent(settings);
}
return super.onOptionsItemSelected(item);
}
//this method starts an intent with the class given to it
public void StartIntent(Class<?> intentclass) {
// TODO Auto-generated method stub
Intent intent = new Intent(this, intentclass);
startActivity(intent);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
/**
* Returns a new instance of this fragment for the given section number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
return rootView;
}
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
((MainActivity) activity).onSectionAttached(getArguments().getInt(
ARG_SECTION_NUMBER));
}
}
}
请记住，我对Android编码相对较新，所以错误可能是我忽略的极其简单的事情。
这可能是因为我最近使用了PagerSlidingTabStrip，但是在主要活动中没有使用PagerSlidingTabStrip。 HMM。
谢谢。
EDIT1 ：发布styles.xml
值-V14：
<resources>
<!--
Base application theme for API 14+. This theme completely replaces
AppBaseTheme from BOTH res/values/styles.xml and
res/values-v11/styles.xml on API 14+ devices.
-->
<style name="AppBaseTheme" parent="Theme.AppCompat.Light.DarkActionBar">
<!-- API 14 theme customizations can go here. -->
</style>
</resources>
值-V11：
<resources>
<!--
Base application theme for API 11+. This theme completely replaces
AppBaseTheme from res/values/styles.xml on API 11+ devices.
-->
<style name="AppBaseTheme" parent="Theme.AppCompat.Light">
<!-- API 11 theme customizations can go here. -->
</style>
</resources>
值：
<!--
Base application theme, dependent on API level. This theme is replaced
by AppBaseTheme from res/values-vXX/styles.xml on newer devices.
-->
<style name="AppBaseTheme" parent="Theme.AppCompat.Light">
<!--
Theme customizations available in newer API levels can go in
res/values-vXX/styles.xml, while customizations related to
backward-compatibility can go here.
-->
</style>
<!-- Application theme. -->
<style name="AppTheme" parent="AppBaseTheme">
<!-- All customizations that are NOT specific to a particular API-level can go here. -->
</style>
</resources>
EDIT2 ：发布activity_main.xml
<!-- A DrawerLayout is intended to be used as the top-level content view using match_parent for both width and height to consume the full space available. -->
<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/drawer_layout"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.pipturner.timetable.MainActivity" >
<!--
As the main content view, the view below consumes the entire
space available using match_parent in both dimensions.
-->
<FrameLayout
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="16dp"
android:paddingRight="16dp"
android:orientation="vertical" >
<TextView
android:id="@+id/lessons"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="2"
android:textAppearance="?android:attr/textAppearanceLarge" />
<Button
android:id="@+id/homeworkbutton"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="0"
android:text="@string/homework" />
<TextView
android:id="@+id/homeworktext"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1" />
</LinearLayout>
</FrameLayout>
<!--
android:layout_gravity="start" tells DrawerLayout to treat
this as a sliding drawer on the left side for left-to-right
languages and on the right side for right-to-left languages.
If you're not building against API 17 or higher, use
android:layout_gravity="left" instead.
-->
<!--
The drawer is given a fixed width in dp and extends the full height of
the container.
-->
<fragment
android:id="@+id/navigation_drawer"
android:name="com.pipturner.timetable.NavigationDrawerFragment"
android:layout_width="@dimen/navigation_drawer_width"
android:layout_height="match_parent"
android:layout_gravity="start"
tools:layout="@layout/fragment_navigation_drawer" />
</android.support.v4.widget.DrawerLayout>
答案 0 :(得分：0)
我通过创建具有更高API最低要求的新项目来解决此错误，然后将所有代码复制到新项目中。不知道为什么或如何运作但是啊。