NullPointerException with ListView and setAdapter_问答_开发者

I keep getting the following nullPointerException and I can't quite figure it out any help would be greatly appreciated. The program query() from DB and then use adapter to populate ListView.

   public class ViewListingsActivity extends Activity {
    SQLiteDatabase db;
    ListView listview;
    Button button;
    SimpleCursorAdapter adapter;
    private static final String TAG = DBHelper.class.getSimpleName();
    public static final String DB_ADDRESS = BaseColumns._ID;
    public static final String DB_DESCRIPTION = "Description";
    public static final String DB_URL = "URL";
    final String dbTable = "Realtor_SMS_Table";

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.viewlisting);
        listview = (ListView) findViewById(R.id.list);
        button = (Button) findViewById(R.id.button1);
        DBHelper dbhelper = new DBHelper(ViewListingsActivity.this);
        db = dbhelper.getWritableDatabase();

        Cursor cursor = db.query(dbTable, null, null, null, null, null, null);
        startManagingCursor(cursor);

        String[] from = new String[] { DB_ADDRESS, DB_DESCRIPTION, DB_URL };
        int[] to = new int[] { R.id.textlistaddress, R.id.textlistdescription,
                R.id.textlisturl };
        adapter = new SimpleCursorAdapter(this, R.layout.rowlist, cursor, from,
                to);
        listview.setAdapter(adapter);

    }
}

here is my stack trace

----- pid 764 at 2011-08-05 13:26:24 -----
Cmd line: com.RealtorSMS

DALVIK THREADS:
"main" prio=5 tid=3 NATIVE
  | group="main" sCount=1 dsCount=0 s=0 obj=0x40018e70
  | sysTid=764 nice=0 sched=0/0 handle=-1096475492
  at android.os.BinderProxy.transact(Native Method)
  at android.app.ActivityManagerProxy.handleApplicationError(ActivityManagerNative.java:2103)
  at com.android.internal.os.RuntimeInit.crash(RuntimeInit.java:302)
  at com.android.internal.os.RuntimeInit$UncaughtHandler.uncaughtException(RuntimeInit.java:75)
  at java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:887)
  at java.lang.ThreadGroup.uncaughtException(ThreadGroup.java:884)
  at dalvik.system.NativeStart.main(Native Method)

"Binder Thread #3" prio=5 tid=15 NATIVE
  | group="main" sCount=1 dsCount=0 s=0 obj=0x43594008
  | sysTid=771 nice=0 sched=0/0 handle=1505008
  at dalvik.system.NativeStart.run(Native Method)

"Binder Thread #2" prio=5 tid=13 NATIVE
  | group="main" sCount=1 dsCount=0 s=0 obj=0x43590120
  | sysTid=770 nice=0 sched=0/0 handle=1487504
  at dalvik.system.NativeStart.run(Native Method)

"Binder Thread #1" prio=5 tid=11 NATIVE
  | group="main" sCount=1 dsCount=0 s=0 obj=0x4358e9b0
  | sysTid=769 nice=0 sched=0/0 handle=1396928
  at dalvik.system.NativeStart.run(Native Method)

"JDWP" daemon prio=5 tid=9 VMWAIT
  | group="system" sCount=1 dsCount=0 s=0 obj=0x4358d2a0
  | sysTid=768 nice=0 sched=0/0 handle=1493656
  at dalvik.system.NativeStart.run(Native Method)

"Signal Catcher" daemon prio=5 tid=7 RUNNABLE
  | group="system" sCount=0 dsCount=0 s=0 obj=0x4358d1e8
  | sysTid=767 nice=0 sched=0/0 handle=1490832
  at dalvik.system.NativeStart.run(Native Method)

"HeapWorker" daemon prio=5 tid=5 VMWAIT
  | group="system" sCount=1 dsCount=0 s=0 obj=0x427d1928
  | sysTid=765 nice=0 sched=0/0 handle=1488192
  at dalvik.system.NativeStart.run(Native Method)

----- end 764 -----

Here are the two xmls

rowlist.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="match_parent"
  android:layout_height="match_parent">
    <TextView android:layout_height="wrap_content" android:text="TextView" android:layout_width="match_parent" android:id="@+id/textlistaddress"></TextView>
    <TextView android:layout_height="wrap_content" android:text="TextView" android:layout_width="match_parent" android:id="@+id/textlistdescription"></TextView>
    <TextView android:layout_height="wrap_content" android:text="TextView" android:layout_width="match_parent" android:id="@+id/textlisturl"></TextView>

</LinearLayout>

viewlisting.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android开发者_运维问答:layout_width="match_parent"
    android:layout_height="match_parent" android:background="@drawable/realtorbackground"
    android:weightSum="1">
    <TextView android:layout_weight="0.08" android:layout_height="wrap_content"
        android:layout_width="match_parent" android:id="@+id/textViewtitleview"
        android:gravity="center" android:textSize="30dp" android:text="Current Listings"></TextView>
    <ListView android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/list"></ListView>
    <Button android:id="@+id/button1" android:layout_width="match_parent"
        android:layout_height="wrap_content" android:text="Delete Listing"></Button>

</LinearLayout>

here is the logcat:

08-05 13:26:24.077: ERROR/AndroidRuntime(764): Uncaught handler: thread main exiting due to uncaught exception
08-05 13:26:24.087: ERROR/AndroidRuntime(764): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.RealtorSMS/com.RealtorSMS.ViewListingsActivity}: java.lang.NullPointerException
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2268)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2284)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at android.app.ActivityThread.access$1800(ActivityThread.java:112)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1692)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at android.os.Looper.loop(Looper.java:123)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at android.app.ActivityThread.main(ActivityThread.java:3948)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at java.lang.reflect.Method.invokeNative(Native Method)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at java.lang.reflect.Method.invoke(Method.java:521)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:782)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:540)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at dalvik.system.NativeStart.main(Native Method)
08-05 13:26:24.087: ERROR/AndroidRuntime(764): Caused by: java.lang.NullPointerException
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at com.RealtorSMS.ViewListingsActivity.onCreate(ViewListingsActivity.java:39)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2231)
08-05 13:26:24.087: ERROR/AndroidRuntime(764):     ... 11 more

check viewlisting.xml, It does not contain ListView with id R.id.list

I guess there is something wrong with the compiler or Eclipse. I ran into this problem tonight as well. But after I renamed the ListView ID, and the XML file gets re-compiled, then it works!

I found sometimes, the changes in the XML file is not automatically rebuilt. And sometimes, the build result of the XML file seems lost.

I had same problem. I found that I used setcontentview() with the wrong argument because I copied and pasted code from another class. I repaired wrong argument and problem solved!

check if you have add in onCreate class method this line:

setContentView(R.layout.your_xml);

An answer of Proapp Aplicativos: "check if you have add in onCreate class method this line: setContentView(R.layout.your_xml);" helped me to resolve a problem.

Run in Eclipse Project -> Clean