关于getActionBar和。setDisplayHomeAsUpEnabled的问题就给大家分享到这里，感谢你花时间阅读本站内容，更多关于AndroidActionBarNullPointerEx
关于getActionBar和。setDisplayHomeAsUpEnabled的问题就给大家分享到这里，感谢你花时间阅读本站内容，更多关于Android ActionBar NullPointerException、Android FragmentManager BackStackRecord.run引发NullPointerException、Android HttpUrlConnection getInputStream引发NullPointerException、Android NullPointerException GetDatabaseLocked等相关知识的信息别忘了在本站进行查找喔。
本文目录一览：- getActionBar（）。setDisplayHomeAsUpEnabled（true）引发NullPointerException（getactionbar为空）
- Android ActionBar NullPointerException
- Android FragmentManager BackStackRecord.run引发NullPointerException
- Android HttpUrlConnection getInputStream引发NullPointerException
- Android NullPointerException GetDatabaseLocked
getActionBar（）。setDisplayHomeAsUpEnabled（true）引发NullPointerException（getactionbar为空）
多次询问了这个问题，我已经尝试了全部。但不幸的是，两者都没有为我工作。
我正在尝试实现两个活动之间的导航，这是学习Android应用程序开发的一部分。我的最小SDK版本和目标SDK版本分别为11和21（Android
5）。我在AndroidManifest.xml中的设置如下所示：
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.navigation" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="11" android:targetSdkVersion="21" /> <application android:allowBackup="true" android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@style/AppTheme" > <activity android:name=".MainActivity" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:name=".DetailActivity" > </activity> </application></manifest>我有两个活动：MainActivity和DetailActivity。当我单击MainActivity中的按钮时，该应用程序成功打开了DetailActivity。但是，当我尝试使用以下代码启用后退按钮时，它将返回NullPointerExcepion：
getActionBar().setDisplayHomeAsUpEnabled(true);我的两个类都扩展了ActionBarActivity。
在MainActivity.java中：
public class MainActivity extends ActionBarActivity {...}在DetailActivity.java中：
public class DetailActivity extends ActionBarActivity{ @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_detail); getActionBar().setDisplayHomeAsUpEnabled(true); // returns null pointer}我也尝试过改变主题。例如，android:theme="@android:style/Theme.Holo.Light"。
答案1
小编典典您是继承自ActionBarActivity。因此，您需要使用getSupportActionBar()而不是getActionBar()来获得-
提供的appcompat-v7操作栏反向端口。
Android ActionBar NullPointerException
我想启用
Android ActionBar,但它对我不起作用.
这是我的MainActivity：
public void onCreate(Bundle savedInstanceState) {
this.requestwindowFeature(Window.FEATURE_NO_TITLE);
super.onCreate(savedInstanceState);
setContentView(R.layout.login);
ActionBar actionBar = getActionBar();
actionBar.show();
//more code............
这是logcat：
03-04 16:31:09.423: E/AndroidRuntime(1441): FATAL EXCEPTION: main
03-04 16:31:09.423: E/AndroidRuntime(1441): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.salebook/com.example.salebook.MainActivity}: java.lang.NullPointerException
03-04 16:31:09.423: E/AndroidRuntime(1441): at android.app.ActivityThread.performlaunchActivity(ActivityThread.java:2180)
03-04 16:31:09.423: E/AndroidRuntime(1441): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
03-04 16:31:09.423: E/AndroidRuntime(1441): at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-04 16:31:09.423: E/AndroidRuntime(1441): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
03-04 16:31:09.423: E/AndroidRuntime(1441): at android.os.Handler.dispatchMessage(Handler.java:99)
03-04 16:31:09.423: E/AndroidRuntime(1441): at android.os.Looper.loop(Looper.java:137)
03-04 16:31:09.423: E/AndroidRuntime(1441): at android.app.ActivityThread.main(ActivityThread.java:5041)
03-04 16:31:09.423: E/AndroidRuntime(1441): at java.lang.reflect.Method.invokeNative(Native Method)
03-04 16:31:09.423: E/AndroidRuntime(1441): at java.lang.reflect.Method.invoke(Method.java:511)
03-04 16:31:09.423: E/AndroidRuntime(1441): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-04 16:31:09.423: E/AndroidRuntime(1441): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-04 16:31:09.423: E/AndroidRuntime(1441): at dalvik.system.NativeStart.main(Native Method)
03-04 16:31:09.423: E/AndroidRuntime(1441): Caused by: java.lang.NullPointerException
03-04 16:31:09.423: E/AndroidRuntime(1441): at com.example.salebook.MainActivity.onCreate(MainActivity.java:130)
03-04 16:31:09.423: E/AndroidRuntime(1441): at android.app.Activity.performCreate(Activity.java:5104)
03-04 16:31:09.423: E/AndroidRuntime(1441): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
03-04 16:31:09.423: E/AndroidRuntime(1441): at android.app.ActivityThread.performlaunchActivity(ActivityThread.java:2144)
03-04 16:31:09.423: E/AndroidRuntime(1441): ... 11 more
第130行是anctionBar.show(),我在res / menu / menu.xml中：
<menu xmlns:android="http://schemas.android.com/apk/res/android">
<item android:id="@+id/itemid_0"
android:title="Action Item 0"
android:icon="@drawable/ic_launcher"
android:orderInCategory="0"
android:showAsAction="ifRoom|withText" />
<item android:id="@+id/itemid_1"
android:title="Action Item 1"
android:orderInCategory="0" />
<item android:id="@+id/itemid_2"
android:title="Action Item 2"
android:orderInCategory="0" />
<item android:id="@+id/itemid_3"
android:title="Action Item 3"
android:orderInCategory="0" />
</menu>
我没有发现问题.希望有人帮助我.
谢谢.
另外,在appThem风格：
<style name="AppTheme" parent="AppBaseTheme">
<item name="android:windowActionBar">true</item>
<!-- All customizations that are NOT specific to a particular API-level can go here. -->
</style>
解决方法
您的Actionbar返回null,因为您没有操作栏但是您正在请求使用getActionbar()
确保您具有显示操作栏的窗口功能,这是操作栏显示所必需的.有关详细信息,请查看以下链接.
…检查此问题getActionBar returns null并查看此链接以获取有关您的问题http://blog.perpetumdesign.com/2011/08/strange-case-of-dr-action-and-mr-bar.html的更多信息
Android FragmentManager BackStackRecord.run引发NullPointerException
使用片段时，有时会出现以下异常：
FATAL EXCEPTION: main
java.lang.NullPointerException
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:591)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1416)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:420)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
当通过尝试从管理器中删除片段时run()，BackStackRecord会通过调用of
发生异常execPendingTransactions()。
case OP_REMOVE: {
Fragment f = op.fragment;
f.mNextAnim = op.exitAnim; <----
mManager.removeFragment(f,mTransition,mTransitionStyle);
}
break;
我似乎无法弄清楚到底是什么原因造成的？我认为这与删除碎片时未正确清理碎片的堆栈有关。
Android HttpUrlConnection getInputStream引发NullPointerException
我正在尝试从以下网址下载图像：
https://hme_player_pictures.s3.amazonaws.com/test-512813ed3b83286c72f376c7-thumb100.jpg
这是堆栈跟踪：
03-21 12:58:04.040: W/System.err(7084): java.lang.NullPointerException
03-21 12:58:04.040: W/System.err(7084): at libcore.net.http.httpconnection$Address.hashCode(httpconnection.java:343)
03-21 12:58:04.045: W/System.err(7084): at java.util.HashMap.get(HashMap.java:298)
03-21 12:58:04.050: W/System.err(7084): at libcore.net.http.httpconnectionPool.get(httpconnectionPool.java:67)
03-21 12:58:04.050: W/System.err(7084): at libcore.net.http.httpconnection.connect(httpconnection.java:128)
03-21 12:58:04.050: W/System.err(7084): at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:308)
03-21 12:58:04.055: W/System.err(7084): at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.makeSslConnection(HttpsURLConnectionImpl.java:460)
03-21 12:58:04.055: W/System.err(7084): at libcore.net.http.HttpsURLConnectionImpl$HttpsEngine.connect(HttpsURLConnectionImpl.java:432)
03-21 12:58:04.055: W/System.err(7084): at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:282)
03-21 12:58:04.060: W/System.err(7084): at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:232)
03-21 12:58:04.065: W/System.err(7084): at libcore.net.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:273)
03-21 12:58:04.065: W/System.err(7084): at libcore.net.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:168)
03-21 12:58:04.070: W/System.err(7084): at libcore.net.http.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:270)
03-21 12:58:04.070: W/System.err(7084): ...
码：
URL imageUrl = new URL(url);
HttpURLConnection c = (HttpURLConnection)imageUrl.openConnection();
InputStream in = c.getInputStream(); // Nullpointer exception on this line, c is definitely not null, I debugged
无法弄清楚为什么会引发NullPointerException.上面的网址确实可以在浏览器中使用.
解决方法:
对于它的价值,我在Android HTTP库中看到很多错误.从条码扫描器中,我可以看到大约3500万人员的堆栈跟踪,因此,我想我已经看到了其中的一切.这是我们在下面的应用程序中发现并吞下的所有怪异内容.我建议您将其作为平台错误来解决,并优雅地失败.
https://code.google.com/p/zxing/source/browse/trunk/android/src/com/google/zxing/client/android/HttpHelper.java
private static int safelyConnect(String uri, HttpURLConnection connection) throws IOException {
try {
connection.connect();
} catch (NullPointerException npe) {
// this is an Android bug: http://code.google.com/p/android/issues/detail?id=16895
Log.w(TAG, "Bad URI? " + uri);
throw new IOException(npe.toString());
} catch (IllegalArgumentException iae) {
// Also seen this in the wild, not sure what to make of it. Probably a bad URL
Log.w(TAG, "Bad URI? " + uri);
throw new IOException(iae.toString());
} catch (SecurityException se) {
// due to bad VPN settings?
Log.w(TAG, "Restricted URI? " + uri);
throw new IOException(se.toString());
} catch (indexoutofboundsexception ioobe) {
// Another Android problem? https://groups.google.com/forum/?fromgroups#!topic/google-admob-ads-sdk/U-WfmYa9or0
Log.w(TAG, "Bad URI? " + uri);
throw new IOException(ioobe.toString());
}
try {
return connection.getResponseCode();
} catch (NullPointerException npe) {
// this is maybe this Android bug: http://code.google.com/p/android/issues/detail?id=15554
Log.w(TAG, "Bad URI? " + uri);
throw new IOException(npe.toString());
} catch (NumberFormatException nfe) {
// Again seen this in the wild for bad header fields in the server response!
Log.w(TAG, "Bad server status? " + uri);
throw new IOException(nfe.toString());
}
}
Android NullPointerException GetDatabaseLocked
我的程序有问题.
我使用数据库来保存我的应用程序的设置.当我在应用程序中保存密码时一切正常,但是当我保存“学校类”的名称时原则上使用相同的方法,但另一个表崩溃并且我收到此错误：
02-19 15:32:04.070: E/AndroidRuntime(14349): FATAL EXCEPTION: main
02-19 15:32:04.070: E/AndroidRuntime(14349): java.lang.NullPointerException
02-19 15:32:04.070: E/AndroidRuntime(14349): at android.database.sqlite.sqliteOpenHelper.getDatabaseLocked(sqliteOpenHelper.java:224)
02-19 15:32:04.070: E/AndroidRuntime(14349): at android.database.sqlite.sqliteOpenHelper.getWritableDatabase(sqliteOpenHelper.java:164)
02-19 15:32:04.070: E/AndroidRuntime(14349): at de.vertretungsplan2.helper.DBHandler.insertKurs(DBHandler.java:95)
02-19 15:32:04.070: E/AndroidRuntime(14349): at de.vertretungsplan2.tabswipe.adapter.KurseFragment$1.onItemClick(KurseFragment.java:38)
02-19 15:32:04.070: E/AndroidRuntime(14349): at android.widget.AdapterView.performItemClick(AdapterView.java:297)
02-19 15:32:04.070: E/AndroidRuntime(14349): at android.widget.AbsListView.performItemClick(AbsListView.java:1100)
02-19 15:32:04.070: E/AndroidRuntime(14349): at android.widget.AbsListView$PerformClick.run(AbsListView.java:2788)
02-19 15:32:04.070: E/AndroidRuntime(14349): at android.widget.AbsListView$1.run(AbsListView.java:3463)
02-19 15:32:04.070: E/AndroidRuntime(14349): at android.os.Handler.handleCallback(Handler.java:730)
02-19 15:32:04.070: E/AndroidRuntime(14349): at android.os.Handler.dispatchMessage(Handler.java:92)
02-19 15:32:04.070: E/AndroidRuntime(14349): at android.os.Looper.loop(Looper.java:137)
02-19 15:32:04.070: E/AndroidRuntime(14349): at android.app.ActivityThread.main(ActivityThread.java:5289)
02-19 15:32:04.070: E/AndroidRuntime(14349): at java.lang.reflect.Method.invokeNative(Native Method)
02-19 15:32:04.070: E/AndroidRuntime(14349): at java.lang.reflect.Method.invoke(Method.java:525)
02-19 15:32:04.070: E/AndroidRuntime(14349): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739)
02-19 15:32:04.070: E/AndroidRuntime(14349): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
02-19 15:32:04.070: E/AndroidRuntime(14349): at dalvik.system.NativeStart.main(Native Method)
这是应该在数据库中写入的方法：
public void insertKurs(String Kurs){
long rowId = -1;
try{
//open Database
sqliteDatabase db = this.getWritableDatabase();
//Content
ContentValues values = new ContentValues();
values.put(KURS_NAME, Kurs);
//insert Values in Table
rowId = db.insert(TABLE_NAME_KURS, null, values);
db.close();
}catch (sqliteException e){
Log.e(TAG,"insert()",e);
}finally{
Log.d(TAG, "insert(): rowId=" + rowId);
}
}
此方法没有任何问题：
public void insertPW(String PW){
sqliteDatabase db = null;
long rowId = -1;
try{
//open Database
db = this.getWritableDatabase();
//Content
ContentValues values = new ContentValues();
values.put(PASSWORD_NAME, PW);
//insert Values in Table
rowId = db.insert(TABLE_NAME_PW, null, values);
db.close();
}catch (sqliteException e){
Log.e(TAG,"insert()",e);
}finally{
Log.d(TAG, "insert(): rowId=" + rowId);
}
}
这是调用另一个的方法：
public void onItemClick(AdapterView<?>arg0,View v, int position,long id){
db.insertKurs(kursView1.getItemAtPosition(position).toString());
}
});
谢谢你的帮助,对不起我的英语：D
解决方法:
传递给sqliteOpenHelper构造函数的Context是null.
关于getActionBar和。setDisplayHomeAsUpEnabled的介绍已经告一段落，感谢您的耐心阅读，如果想了解更多关于Android ActionBar NullPointerException、Android FragmentManager BackStackRecord.run引发NullPointerException、Android HttpUrlConnection getInputStream引发NullPointerException、Android NullPointerException GetDatabaseLocked的相关信息，请在本站寻找。
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