问题
Hi i'm new bee to android. while executing my application I'm getting nullpoint exception error, dont know why it is happening. please any one help me to get rid from this issue. thanks in advance.
This is my logcat:
09-14 12:30:14.027: INFO/System.out(365): Constructor StudentList Adapter...
09-14 12:30:14.027: DEBUG/AndroidRuntime(365): Shutting down VM
09-14 12:30:14.027: WARN/dalvikvm(365): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): FATAL EXCEPTION: main
09-14 12:30:14.047: ERROR/AndroidRuntime(365): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.UserLogin/com.UserLogin.FindPlaces}: java.lang.NullPointerException
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.app.ActivityThread.startActivityNow(ActivityThread.java:2503)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:651)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.widget.TabHost.setCurrentTab(TabHost.java:323)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.widget.TabHost$2.onTabSelectionChanged(TabHost.java:129)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.widget.TabWidget$TabClickListener.onClick(TabWidget.java:453)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.view.View.performClick(View.java:2408)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.view.View$PerformClick.run(View.java:8816)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.os.Handler.handleCallback(Handler.java:587)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.os.Handler.dispatchMessage(Handler.java:92)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.os.Looper.loop(Looper.java:123)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.app.ActivityThread.main(ActivityThread.java:4627)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at java.lang.reflect.Method.invokeNative(Native Method)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at java.lang.reflect.Method.invoke(Method.java:521)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at dalvik.system.NativeStart.main(Native Method)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): Caused by: java.lang.NullPointerException
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at com.UserLogin.FindPlaces.displayLocs(FindPlaces.java:35)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at com.UserLogin.FindPlaces.onCreate(FindPlaces.java:30)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
09-14 12:30:14.047: ERROR/AndroidRuntime(365): ... 18 more
09-14 12:30:14.057: WARN/ActivityManager(58): Force finishing activity com.UserLogin/.Innerpage
09-14 12:30:14.594: WARN/ActivityManager(58): Activity pause timeout for HistoryRecord{4506eef0 com.UserLogin/.Innerpage}
09-14 12:30:16.347: INFO/Process(365): Sending signal. PID: 365 SIG: 9
09-14 12:30:16.367: INFO/ActivityManager(58): Process com.UserLogin (pid 365) has died.
09-14 12:30:16.367: INFO/WindowManager(58): WIN DEATH: Window{4506a6e0 com.UserLogin/com.UserLogin.Innerpage paused=false}
09-14 12:30:16.367: INFO/WindowManager(58): WIN DEATH: Window{451492d0 com.UserLogin/com.UserLogin.UserLogin paused=false}
09-14 12:30:16.397: INFO/UsageStats(58): Unexpected resume of com.android.launcher while already resumed in com.UserLogin
Java file:
import java.util.ArrayList;
import android.app.ListActivity;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
public class FindPlaces extends ListActivity{
private SQLiteDatabase DbLoc;
ListView lv;
private ArrayList<Fields> results = new ArrayList<Fields>();
@Override
public void onCreate(Bundle savedInstance) {
super.onCreate(savedInstance);
//setContentView(R.layout.places);
getallLocs();
displayLocs();
}
private void displayLocs() {
lv = (ListView)findViewById(R.id.listPlaces);
lv.setAdapter(new StudentListAdapter(this, R.layout.placeslist, results));
//lv.setAdapter(new ArrayAdapter<Fields>(this,android.R.layout.simple_list_item_1, results));
}
class StudentListAdapter extends ArrayAdapter<Fields>{
private ArrayList<Fields> locationDetails;
private Context mContext;
public StudentListAdapter(Context context,int textViewResourceId, ArrayList<Fields> results) {
super(context, textViewResourceId, results);
// TODO Auto-generated constructor stub
System.out.println("Constructor StudentList Adapter...");
this.locationDetails = results;
mContext = context;
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return results.size();
}
@Override
public Fields getItem(int position) {
// TODO Auto-generated method stub
return locationDetails.get(position);
}
@Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return super.getItemId(position);
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
// TODO Auto-generated method stub
View v = convertView;
if(v == null){
LayoutInflater vl = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
v = vl.inflate(R.layout.placeslist, null);
}
Fields o = results.get(position);
if (o != null) {
TextView iv = (TextView)v.findViewById(R.id.toptext);
TextView tv_sNo = (TextView)v.findViewById(R.id.toptext1);
iv.setText(o.getLocationName());
tv_sNo.setText(o.getLocationImage());
}
DbLoc.close();
return v;
}
}
static class ViewHolder
{
TextView Locationname;
ImageView Locationimage;
}
private void getallLocs() {
// TODO Auto-generated method stub
try {
DatabaseHelper dbHelper = new DatabaseHelper(
this.getApplicationContext());
DbLoc = dbHelper.getWritableDatabase();
Cursor c = DbLoc.rawQuery("SELECT " + DatabaseHelper.LocationName+ " , " + DatabaseHelper.LocationImage + " FROM "
+ DatabaseHelper.LOCATIONTABLE , null);
if (c != null) {
if (c.moveToFirst()) {
do {
String LocationName= c.getString(c.getColumnIndex("LocationName"));
String Mobile = c.getString(c
.getColumnIndex("LocationImage"));
Fields p = new Fields(LocationName, Mobile);
results.add(p);
} while (c.moveToNext());
}
}
} catch (SQLiteException se) {
Log.e(getClass().getSimpleName(),
"Could not create or Open the database");
}
finally { if (DbLoc != null) DbLoc.execSQL("DELETE FROM " +
DatabaseHelper.FRIENDTABLE); DbLoc.execSQL("DELETE FROM " +
DatabaseHelper.LOCATIONTABLE);
DbLoc.execSQL("DROP TABLE IF EXISTS tablename"+ DatabaseHelper.FRIENDTABLE);
DbLoc.execSQL("DROP TABLE IF EXISTS tablename"+ DatabaseHelper.LOCATIONTABLE);
DbLoc.close();
}
}
}
Places.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent" android:padding="6dip">
<ListView android:id="@+id/listPlaces" android:layout_width="fill_parent"
android:layout_height="wrap_content" />
</LinearLayout>
Placeslist.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="wrap_content">
<TextView android:id="@+id/toptext" android:layout_width="fill_parent"
android:layout_height="0dip" android:layout_weight="1"
android:gravity="center_vertical" />
<TextView android:id="@+id/toptext1" android:layout_width="fill_parent"
android:layout_height="0dip" android:layout_weight="1"
android:gravity="center_vertical" />
</LinearLayout>
回答1:
uncomment this line
setContentView(R.layout.places);
EDITED:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="fill_parent"
android:layout_height="fill_parent" android:padding="6dip">
<ListView android:id="@android:id/list" android:layout_width="fill_parent"
android:layout_height="wrap_content" />
</LinearLayout>
replace this with your file(Places.xml)
UPDATED
public void onCreate(Bundle savedInstance) {
super.onCreate(savedInstance);
//setContentView(R.layout.places);
getallLocs();
setListAdapter(new ArrayAdapter<Fields>(this,android.R.layout.simple_list_item_1, results));
// displayLocs();
}
private void displayLocs() {
lv = (ListView)findViewById(R.id.listPlaces);
lv.setAdapter(new StudentListAdapter(this, R.layout.placeslist, results));
//lv.setAdapter(new ArrayAdapter<Fields>(this,android.R.layout.simple_list_item_1, results));
}
回答2:
You can't use findViewById() if you haven't set a content-view for the activity. So your lv will be null.
You're using a ListActivity. If you want to add your own style to it, the ListView in your layout needs the id android:list:
<ListView android:id="@android:id/list"
...
/>
As illustrated here.
If you use a ListActivity, you don't use findViewById() to get the ListView, you can use the getListView()-method.
来源：https://stackoverflow.com/questions/7412599/error-androidruntime335-caused-by-java-lang-nullpointerexception