java - Null Pointer Exception with Dialog Android

i have this Dialog and i would like to show it when i click on a preference

public class ADialog extends AlertDialog.Builder {

    public ADialog(Context arg0) {
        super(arg0);
        final LayoutInflater inflater = LayoutInflater.from(arg0);
        final View Viewlayout = inflater.inflate(R.layout.myLayout, null);


        setTitle("Text Dialog");
        setView(Viewlayout);

        setNeutralButton("CLOSE",
                new DialogInterface.OnClickListener() {
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
            });


        create();
        show();
    }
}

This is the code from Preference

Context context;
    Pref = (Preference) this.findPreference("pref");

            pref.setOnPreferenceClickListener(new OnPreferenceClickListener(){  
                @Override
                public boolean onPreferenceClick(Preference preference) {
                    // TODO Auto-generated method stub
                    ADialog dialog = new ADialog(context);

                    return false;


                }});

I'm getting a Java Null Pointer Exception in super(arg0); Why?

THIS IS THE LOGCAT. Settings line 57 correspond to ADialog dialog = new ADialog(context);

> 11-17 18:15:45.416: E/AndroidRuntime(14709): FATAL EXCEPTION: main
> 11-17 18:15:45.416: E/AndroidRuntime(14709):
> java.lang.NullPointerException 11-17 18:15:45.416:
> E/AndroidRuntime(14709):  at

> android.app.AlertDialog.resolveDialogTheme(AlertDialog.java:143) 11-17
> 18:15:45.416: E/AndroidRuntime(14709):    at
> android.app.AlertDialog$Builder.(AlertDialog.java:360) 11-17
> 18:15:45.416: E/AndroidRuntime(14709):    at
> com.packagename.ADialog.(Dialog.java:21) 11-17 18:15:45.416:
> E/AndroidRuntime(14709):  at
> com.packagename.Settings$1.onPreferenceClick(Settings.java:57)
> 11-17 18:15:45.416: E/AndroidRuntime(14709):  at
> android.preference.Preference.performClick(Preference.java:952) 11-17
> 18:15:45.416: E/AndroidRuntime(14709):    at

> android.preference.PreferenceScreen.onItemClick(PreferenceScreen.java:215)
> 11-17 18:15:45.416: E/AndroidRuntime(14709):  at
> android.widget.AdapterView.performItemClick(AdapterView.java:297)
> 11-17 18:15:45.416: E/AndroidRuntime(14709):  at
> android.widget.AbsListView.performItemClick(AbsListView.java:1100)
> 11-17 18:15:45.416: E/AndroidRuntime(14709):  at
> android.widget.AbsListView$PerformClick.run(AbsListView.java:2788)
> 11-17 18:15:45.416: E/AndroidRuntime(14709):  at
> android.widget.AbsListView$1.run(AbsListView.java:3463) 11-17
> 18:15:45.416: E/AndroidRuntime(14709):    at

> android.os.Handler.handleCallback(Handler.java:730) 11-17
> 18:15:45.416: E/AndroidRuntime(14709):    at
> android.os.Handler.dispatchMessage(Handler.java:92) 11-17
> 18:15:45.416: E/AndroidRuntime(14709):    at
> android.os.Looper.loop(Looper.java:137) 11-17 18:15:45.416:
> E/AndroidRuntime(14709):  at
> android.app.ActivityThread.main(ActivityThread.java:5289) 11-17
> 18:15:45.416: E/AndroidRuntime(14709):    at
> java.lang.reflect.Method.invokeNative(Native Method) 11-17
> 18:15:45.416: E/AndroidRuntime(14709):    at

> java.lang.reflect.Method.invoke(Method.java:525) 11-17 18:15:45.416:
> E/AndroidRuntime(14709):  at
> com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739)
> 11-17 18:15:45.416: E/AndroidRuntime(14709):  at
> com.android.internal.os.ZygoteInit.main(ZygoteInit.java:555) 11-17
> 18:15:45.416: E/AndroidRuntime(14709):    at
> dalvik.system.NativeStart.main(Native Method

I've also this

    Context mContext;

audioManager = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);

For use it in this class i used the Context but the logcat is a Java Null Pointer Exception

Answer

here you are passing null context so pass the correct context

ADialog dialog = new ADialog(context);

into

ADialog dialog = new ADialog(getAppicationContext());s..

or add like this

Context context=getApplicationContext()