java - How to debug a NullPointerException in an Android app?

Question

I have a very simple app which isn't starting correctly. The app should load a splashscreen, and then the main app. For some reason it's now not working -

Logcat:

    02-08 13:30:41.846: E/AndroidRuntime(275): Uncaught handler: thread main exiting due to uncaught exception
02-08 13:30:41.865: E/AndroidRuntime(275): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.KES.GApps/com.KES.GApps.Splashscreen}: java.lang.NullPointerException
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.app.ActivityThread.access$2200(ActivityThread.java:119)
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.os.Handler.dispatchMessage(Handler.java:99)
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.os.Looper.loop(Looper.java:123)
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.app.ActivityThread.main(ActivityThread.java:4363)
02-08 13:30:41.865: E/AndroidRuntime(275):  at java.lang.reflect.Method.invokeNative(Native Method)
02-08 13:30:41.865: E/AndroidRuntime(275):  at java.lang.reflect.Method.invoke(Method.java:521)
02-08 13:30:41.865: E/AndroidRuntime(275):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
02-08 13:30:41.865: E/AndroidRuntime(275):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
02-08 13:30:41.865: E/AndroidRuntime(275):  at dalvik.system.NativeStart.main(Native Method)
02-08 13:30:41.865: E/AndroidRuntime(275): Caused by: java.lang.NullPointerException
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.view.ViewGroup.addViewInner(ViewGroup.java:1860)
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.view.ViewGroup.addView(ViewGroup.java:1756)
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.view.ViewGroup.addView(ViewGroup.java:1736)
02-08 13:30:41.865: E/AndroidRuntime(275):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:217)
02-08 13:30:41.865: E/AndroidRuntime(275):  at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:207)
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.app.Activity.setContentView(Activity.java:1633)
02-08 13:30:41.865: E/AndroidRuntime(275):  at com.KES.GApps.Splashscreen.onCreate(Splashscreen.java:13)
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
02-08 13:30:41.865: E/AndroidRuntime(275):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)
02-08 13:30:41.865: E/AndroidRuntime(275):  ... 11 more
02-08 13:30:41.884: I/dalvikvm(275): threadid=7: reacting to signal 3
02-08 13:30:41.884: E/dalvikvm(275): Unable to open stack trace file '/data/anr/traces.txt': Permission denied

xml for the splashscreen (welcome.xml):

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="@drawable/img1"
    android:orientation="vertical" >

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:layout_height="200dp"
        android:layout_gravity="fill_horizontal"
        android:contentDescription="@string/crestinfo"
        android:src="@drawable/logov2" />

    <TextView
        android:id="@+id/welcomescreen"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:gravity="right"
        android:text="@string/welcomescreen"
        android:textAppearance="?android:attr/textAppearanceLarge"
        android:textColor="#ffffff"
        android:textStyle="bold" android:padding="5dp" android:textSize="15pt" />

</LinearLayout>

java:

package com.KES.GApps;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;


public class Splashscreen extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.welcome);
        Thread splashThread = new Thread() {
            @Override
            public void run() {
               try {
                  int waited = 0;
                  while (waited < 2000) {
                     sleep(100);
                     waited += 100;
                  }
               } catch (InterruptedException e) {
                  // do nothing
               } finally {
                  finish();
                  Intent i = new Intent();
                  i.setClassName("com.KES.GApps",
                                 "com.KES.GApps.KingEdwardVIISchoolActivity");
                  startActivity(i);
               }
            }
         };
         splashThread.start();
    }
}

Manifest file:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.KES.GApps"
    android:versionCode="6"
    android:versionName="1.5" >

    <uses-sdk android:minSdkVersion="7" />

    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:name="KingEdwardVIISchool"
        android:debuggable="true"
        android:icon="@drawable/icon"
        android:label="@string/app_name"
        android:launchMode="standard" >
        <activity
            android:name="KingEdwardVIISchoolActivity"
            android:configChanges="orientation|keyboardHidden"
            android:label="@string/app_name"
            android:screenOrientation="portrait" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
            </intent-filter>
        </activity>
        <activity
            android:name="Splashscreen"
            android:configChanges="orientation|keyboardHidden"
            android:label="@string/app_name"
            android:screenOrientation="portrait" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Answer 1

According to the LogCat output the problem is in your welcome.xml layout file. It is inflated incorrectly for some reason.

Try removing android:textAppearance="?android:attr/textAppearanceLarge" attribute and ENSURE that you have run Clean.. command on your project before the launch.

Also ENSURE that all the references in the xml-file are valid (i.e. logov2, img1). I would temporarily remove all references from your xml-file and check if it helps.