Question

I am new at Android. I am getting errors java.lang.NullPointerException and java.lang.RuntimeException application force closes.

10-18 06:04:12.676: E/AndroidRuntime(340): FATAL EXCEPTION: main
10-18 06:04:12.676: E/AndroidRuntime(340): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.md.ExpertRemote/com.md.ExpertRemote.first.ExpertRemote}: java.lang.NullPointerException
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.app.ActivityThread.access$2300(ActivityThread.java:125)
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.os.Handler.dispatchMessage(Handler.java:99)
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.os.Looper.loop(Looper.java:123)
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.app.ActivityThread.main(ActivityThread.java:4627)
10-18 06:04:12.676: E/AndroidRuntime(340):  at java.lang.reflect.Method.invokeNative(Native Method)
10-18 06:04:12.676: E/AndroidRuntime(340):  at java.lang.reflect.Method.invoke(Method.java:521)
10-18 06:04:12.676: E/AndroidRuntime(340):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
10-18 06:04:12.676: E/AndroidRuntime(340):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
10-18 06:04:12.676: E/AndroidRuntime(340):  at dalvik.system.NativeStart.main(Native Method)
10-18 06:04:12.676: E/AndroidRuntime(340): Caused by: java.lang.NullPointerException
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.view.ViewGroup.addViewInner(ViewGroup.java:1969)
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.view.ViewGroup.addView(ViewGroup.java:1865)
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.view.ViewGroup.addView(ViewGroup.java:1845)
10-18 06:04:12.676: E/AndroidRuntime(340):  at com.md.ExpertRemote.first.ExpertRemote.onCreate(ExpertRemote.java:286)
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-18 06:04:12.676: E/AndroidRuntime(340):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
10-18 06:04:12.676: E/AndroidRuntime(340):  ... 11 more

Answer 1

Given the stack trace, it looks like this line:

at com.md.ExpertRemote.first.ExpertRemote.onCreate(ExpertRemote.java:286)

… is probably calling ViewGroup.addView() and passing a null value as one of the arguments. That argument is only being validated a few levels down, hence the extra lines of the stack trace.

Look at line 286 in ExpertRemote.java, and work out why one of the values could be null. (In my experience of questions like this, it’s often because you’re using the wrong kind of ID to find an object.) Unfortunately we can’t give more specific help than that without seeing the code.

It’s important to use this as a learning experience in three respects:

• Learn how to read stack traces. One very simple first pass is to find the first place where your code is mentioned.
• Learn how to use the debugger. While I haven’t done any Android development myself, I’d expect that when running in the debugger, the exception would trigger execution to pause at the problematic place. Even if it doesn’t, using a debugger will help you to validate any diagnosis of the problem (e.g. checking that the argument value really is null)
• Learn how to post better questions: think about what you’d need to know if you were trying to solve the problem. Of course, doing this should also help you to solve your own problems in the first place…