It's apparently a question that has been asked multiple times, but only has solutions on a case-by-case basis. I'm designing an application called Trackr, and all it does is opening a service when a button is pressed. I keep getting this error:
11-13 16:44:06.546: D/ActivityThread(4656): setTargetHeapUtilization:0.25
11-13 16:44:06.546: D/ActivityThread(4656): setTargetHeapIdealFree:8388608
11-13 16:44:06.546: D/ActivityThread(4656): setTargetHeapConcurrentStart:2097152
11-13 16:44:06.926: W/dalvikvm(4656): threadid=1: thread exiting with uncaught exception (group=0x41225438)
11-13 16:44:06.936: E/AndroidRuntime(4656): FATAL EXCEPTION: main
11-13 16:44:06.936: E/AndroidRuntime(4656): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.trackr/com.example.trackr.StartScreen}: java.lang.NullPointerException
11-13 16:44:06.936: E/AndroidRuntime(4656): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
11-13 16:44:06.936: E/AndroidRuntime(4656): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
11-13 16:44:06.936: E/AndroidRuntime(4656): at android.app.ActivityThread.access$700(ActivityThread.java:143)
11-13 16:44:06.936: E/AndroidRuntime(4656): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1241)
11-13 16:44:06.936: E/AndroidRuntime(4656): at android.os.Handler.dispatchMessage(Handler.java:99)
11-13 16:44:06.936: E/AndroidRuntime(4656): at android.os.Looper.loop(Looper.java:137)
11-13 16:44:06.936: E/AndroidRuntime(4656): at android.app.ActivityThread.main(ActivityThread.java:4962)
11-13 16:44:06.936: E/AndroidRuntime(4656): at java.lang.reflect.Method.invokeNative(Native Metood)
11-13 16:44:06.936: E/AndroidRuntime(4656): at java.lang.reflect.Method.invoke(Method.java:511)
11-13 16:44:06.936: E/AndroidRuntime(4656): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1004)
11-13 16:44:06.936: E/AndroidRuntime(4656): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:771)
11-13 16:44:06.936: E/AndroidRuntime(4656): at dalvik.system.NativeStart.main(Native Method)
11-13 16:44:06.936: E/AndroidRuntime(4656): Caused by: java.lang.NullPointerException
11-13 16:44:06.936: E/AndroidRuntime(4656): at com.example.trackr.StartScreen.onCreate(StartScreen.java:17)
11-13 16:44:06.936: E/AndroidRuntime(4656): at android.app.Activity.performCreate(Activity.java:5160)
11-13 16:44:06.936: E/AndroidRuntime(4656): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
11-13 16:44:06.936: E/AndroidRuntime(4656): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)
11-13 16:44:06.936: E/AndroidRuntime(4656): ... 11 more
I have 2 classes, StartScreen(an activity) and StartService(a service). I also have a Manifest for the app and layout files for each one.
package com.example.trackr;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
public class StartScreen extends Activity {
Intent startMonitor;
Button newBut;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_start_screen);
startMonitor.setClassName("com.example.trackr","StartService");
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.start_screen, menu);
return true;
}
public void callService(View view){
startService(startMonitor);
}
}
This is the layout file:
<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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".StartScreen" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_centerHorizontal="true"
android:layout_marginBottom="90dp"
android:onClick="callService"
android:text="Enable" />
</RelativeLayout>
And then this is the manifest file:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.trackr"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="18" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.trackr.StartScreen"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<service android:name="com.example.trackr.StartService"></service>
</application>
</manifest>
I know it may seem like an easy question, but it's got me stumped. I would really appreciate some help. Thanks!
