当我尝试访问我的 ActionBar 时，出现 nullPointerException
getActionBar().setDisplayHomeAsUpEnabled(true);
我的收件人 Activity 是这样的
package com.ahmetyuva.ribbit;
import android.app.AlertDialog;
import android.app.ListActivity;
import android.support.v4.app.NavUtils;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import com.parse.FindCallback;
import com.parse.ParseException;
import com.parse.ParseQuery;
import com.parse.ParseRelation;
import com.parse.ParseUser;
import java.util.List;
public class RecipientsActivity extends ListActivity{
public static final String TAG = RecipientsActivity.class.getSimpleName();
protected List<ParseUser> mFriends;
protected ParseRelation<ParseUser> mFriendsRelation;
protected ParseUser mCurrentUser;
protected MenuItem mSendMenuItem;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_recipients);
getActionBar().setDisplayHomeAsUpEnabled(true);
getListView().setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);
}
@Override
public void onResume() {
super.onResume();
mCurrentUser = ParseUser.getCurrentUser();
mFriendsRelation = mCurrentUser.getRelation(ParseConstants.KEY_FRIENDS_RELATION);
ParseQuery<ParseUser> query = mFriendsRelation.getQuery();
query.addAscendingOrder(ParseConstants.KEY_USERNAME);
query.findInBackground(new FindCallback<ParseUser>() {
@Override
public void done(List<ParseUser> friends, ParseException e) {
if(e == null) {
mFriends = friends;
String[] usernames = new String[mFriends.size()];
int i = 0;
for (ParseUser user : mFriends) {
usernames[i] = user.getUsername();
i++;
} ArrayAdapter<String> adapter = new ArrayAdapter<String>(
getListView().getContext(),
android.R.layout.simple_list_item_checked,
usernames);
setListAdapter(adapter);
}
else{
Log.e(TAG, e.getMessage());
AlertDialog.Builder builder = new AlertDialog.Builder(RecipientsActivity.this);
builder.setMessage(e.getMessage())
.setTitle(R.string.error_title)
.setPositiveButton(android.R.string.ok, null);
AlertDialog dialog = builder.create();
dialog.show();
}
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_recipients, menu);
mSendMenuItem = menu.getItem(0);
return true;
}
@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.
switch (item.getItemId()){
case android.R.id.home:
NavUtils.navigateUpFromSameTask(this);
return true;
case R.id.action_send:
return true;
}
/* int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
*/
return super.onOptionsItemSelected(item);
}
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
super.onListItemClick(l, v, position, id);
if (l.getCheckedItemCount() > 0) {
mSendMenuItem.setVisible(true);
} else {
mSendMenuItem.setVisible(false);
}
}
}
我的错误日志在这里
04-13 11:19:05.148 1956-1956/? E/AndroidRuntime﹕ FATAL EXCEPTION: main java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ahmetyuva.ribbit/com.ahmetyuva.ribbit.RecipientsActivity}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) at android.app.ActivityThread.access$600(ActivityThread.java:141) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:5041) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at com.ahmetyuva.ribbit.RecipientsActivity.onCreate(RecipientsActivity.java:40) at android.app.Activity.performCreate(Activity.java:5104) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) at android.app.ActivityThread.access$600(ActivityThread.java:141) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:5041) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) at dalvik.system.NativeStart.main(Native Method)
menu_recipients xml 在这里
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
tools:context="com.ahmetyuva.ribbit.RecipientsActivity">
<item android:id="@+id/action_send"
android:title="Send"
android:orderInCategory="100"
app:showAsAction="always"
android:visible="true"
android:icon="@drawable/ic_action_send_now"
/>
</menu>
activity_recipients xml 在这里
<RelativeLayout 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"
tools:context="com.ahmetyuva.ribbit.RecipientsActivity">
<ListView
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:id="@android:id/list"
android:layout_alignParentEnd="true"
android:layout_alignParentTop="true"/>
<TextView
android:id="@android:id/empty"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="@string/empty_recipients_list_message"
/>
</RelativeLayout>
list
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.ahmetyuva.ribbit" >
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-feature
android:name="android.hardware.camera"
android:required="true" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="android.permission.VIBRATE" />
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
<uses-permission android:name="android.permission.GET_ACCOUNTS" />
<uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />
<!--
IMPORTANT: Change "com.parse.starter.permission.C2D_MESSAGE" in the lines below
to match your app's package name + ".permission.C2D_MESSAGE".
-->
<permission
android:name="com.ahmetyuva.ribbit.permission.C2D_MESSAGE"
android:protectionLevel="signature" />
<uses-permission android:name="com.ahmetyuva.ribbit.permission.C2D_MESSAGE" />
<application
android:name=".RibbitApplication"
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
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:name=".LoginActivity"
android:label="@string/title_activity_login"
android:screenOrientation="portrait" >
</activity>
<activity
android:name=".SignUpActivity"
android:label="@string/title_activity_sign_up"
android:parentActivityName=".LoginActivity"
android:screenOrientation="portrait" >
</activity>
<activity
android:name=".EditFriendsActivity"
android:label="@string/title_activity_edit_friends"
android:parentActivityName=".MainActivity" >
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.ahmetyuva.ribbit.MainActivity" />
</activity>
<service android:name="com.parse.PushService" />
<receiver android:name="com.parse.ParseBroadcastReceiver" >
<intent-filter>
<action android:name="android.intent.action.BOOT_COMPLETED" />
<action android:name="android.intent.action.USER_PRESENT" />
</intent-filter>
</receiver>
<receiver
android:name="com.parse.ParsePushBroadcastReceiver"
android:exported="false" >
<intent-filter>
<action android:name="com.parse.push.intent.RECEIVE" />
<action android:name="com.parse.push.intent.DELETE" />
<action android:name="com.parse.push.intent.OPEN" />
</intent-filter>
</receiver>
<receiver
android:name="com.parse.GcmBroadcastReceiver"
android:permission="com.google.android.c2dm.permission.SEND" >
<intent-filter>
<action android:name="com.google.android.c2dm.intent.RECEIVE" />
<action android:name="com.google.android.c2dm.intent.REGISTRATION" />
<!-- IMPORTANT: Change "com.parse.starter" to match your app's package name. -->
<category android:name="com.ahmetyuva.ribbit" />
</intent-filter>
</receiver>
<activity
android:name=".RecipientsActivity"
android:label="@string/title_activity_recipients"
android:parentActivityName=".MainActivity"
android:screenOrientation="portrait">
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="com.ahmetyuva.ribbit.MainActivity" />
</activity>
</application>
</manifest>
最佳答案
尝试使用
getSupportedActionBar() instead of getActionBar()
关于java - 访问 ActionBar 时出现 nullPointerException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29606261/