CODEWITHSUNDEEP
javaandroidandroid-activitynullpointerexceptionandroid-context
Andres Y.
Andres Y.

Reputation: 170

Android Activity Context NullPointerException

I'm having some strange errors reports on Google Play Developer Console regarding NPEs on Activity context or Application context. I can't recreate this error on my device and I know it's working fine on most devices.

This is my Main Activity, the one that is first opened on app startup:

public class ActSplash extends Activity {
  private Sync sync;
  private Context ctx;

@Override
public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.act_splash);

  do {
      ctx = this.getApplicationContext(); //Using just "this" doesn't work either.
  } while (ctx==null);

  sync = Sync.getInstance(ctx); //Apparently ctx is null at this point in some devices
}

This is my Sync class (Singleton)

public class Sync {
   private Context ctx;
   private static Sync INSTANCE = null;

   public static Sync getInstance(Context ctx) {
      if (INSTANCE == null) createInstance(ctx);
      return INSTANCE;
   }

   private synchronized static void createInstance(Context ctx) {
      if (INSTANCE == null) { 
        INSTANCE = new Sync(ctx);
      }
   }

   private Sync(Context _ctx)
   {
      ctx = _ctx;
      //NPE on following line
      WifiManager wifiMan = (WifiManager) ctx.getSystemService(Context.WIFI_SERVICE);
      ...
   }

This is the stack trace:

java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.xxx.xxx/com.xxx.xxx.ActSplash}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2178)
at android.app.ActivityThread.access$700(ActivityThread.java:141)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1271)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:5118)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:792)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.xxx.xxx.Sync.<init>(SourceFile:82)
at com.xxx.xxx.Sync.void createInstance(android.content.Context)(SourceFile:67)
at com.xxx.xxx.Sync.com.xxx.xxx.Sync getInstance(android.content.Context)(SourceFile:72)
at com.xxx.xxx.ActSplash.void onCreate(android.os.Bundle)(SourceFile:40)
at android.app.Activity.performCreate(Activity.java:5058)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2104)
... 11 more

What can I do to make sure I have ctx!=null before calling: 

sync = Util_Sync.getInstance(ctx);

Upvotes: 0

Views: 3319

Answers (3)

mangusta
mangusta

Reputation: 3544

Would you mind posting the full constructor ? null pointer exception occurs somewhere inside of Sync() constructor. _ctx is not null though

Upvotes: 0

Scary Wombat
Scary Wombat

Reputation: 44834

so as you have code that does not change

do {
  ctx = this.getApplicationContext(); //Using just "this" doesn't work either.
} while (ctx==null);

this is going to result in an endless loop, if it fails to get ctx.

Activity is a context! See http://developer.android.com/reference/android/content/Context.html

Known Indirect Subclasses AbstractInputMethodService, AccessibilityService, AccountAuthenticatorActivity, ActionBarActivity, Activity, ActivityGroup, AliasActivity, Application, BackupAgent, BackupAgentHelper, ContextThemeWrapper, and 23 others.

Try

ctx = this;

Update

Further to your Sync code being posted

private Context ctx;

is never used, so remove it.

Upvotes: 1

Code-Apprentice
Code-Apprentice

Reputation: 83527

Note that this can never be null. Assume to the contrary that it can be, then this means you would have a call such as myObj.myMethod() where myObj is null. But then this method call would throw a NPE before execution enters myMethod().

This means that your error is coming from somewhere else.

Upvotes: 0

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