Question

I am building an Android application and I have chosen to use flat flies in external storage for my persistence method. I have a class that extends Application with some static instance methods. After debugging a few times, I note that none of the instance variables are null, and the NullPointerException is coming from within Context.getExternalFilesDir(null).

I would like to preface any answers with it is not returning null. Also, I have the correct permissions in my manifest, as well as a check for if the SD card is mounted to the device.

This is the class that holds the call to getExternalFilesDir(null) and throws the error.

public class WhileImOut extends Application {

    public static TaskManager taskManager;
    private static Context appContext;

    public WhileImOut() {
        super();
        appContext = this;
        initialize();
    }

    public static void initialize() {
        if (taskManager == null && Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
            try{
            File f = appContext.getExternalFilesDir(null); // Exception being thrown here
            taskManager = new TaskManager(f.getAbsolutePath());
            }catch(NullPointerException e){
                Log.d("Bad","NPE");
            }catch(Exception e){

            }
        }
    }
}

This is in my AndroidManifest.xml:

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

Any help would be greatly appreciated. I’ve been struggling with this for a few hours, and I will take any advice that is given. Thank you

EDIT: LogCat information

10-10 18:55:56.424: E/AndroidRuntime(964): FATAL EXCEPTION: main
10-10 18:55:56.424: E/AndroidRuntime(964): java.lang.RuntimeException: Unable to resume activity {zsmith.capstone.whileimout/zsmith.capstone.whileimout.TaskListActivity}: java.lang.NullPointerException
10-10 18:55:56.424: E/AndroidRuntime(964):  at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2575)
10-10 18:55:56.424: E/AndroidRuntime(964):  at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2603)
10-10 18:55:56.424: E/AndroidRuntime(964):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2089)
10-10 18:55:56.424: E/AndroidRuntime(964):  at android.app.ActivityThread.access$600(ActivityThread.java:130)
10-10 18:55:56.424: E/AndroidRuntime(964):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
10-10 18:55:56.424: E/AndroidRuntime(964):  at android.os.Handler.dispatchMessage(Handler.java:99)
10-10 18:55:56.424: E/AndroidRuntime(964):  at android.os.Looper.loop(Looper.java:137)
10-10 18:55:56.424: E/AndroidRuntime(964):  at android.app.ActivityThread.main(ActivityThread.java:4745)
10-10 18:55:56.424: E/AndroidRuntime(964):  at java.lang.reflect.Method.invokeNative(Native Method)
10-10 18:55:56.424: E/AndroidRuntime(964):  at java.lang.reflect.Method.invoke(Method.java:511)
10-10 18:55:56.424: E/AndroidRuntime(964):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
10-10 18:55:56.424: E/AndroidRuntime(964):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
10-10 18:55:56.424: E/AndroidRuntime(964):  at dalvik.system.NativeStart.main(Native Method)
10-10 18:55:56.424: E/AndroidRuntime(964): Caused by: java.lang.NullPointerException
10-10 18:55:56.424: E/AndroidRuntime(964):  at zsmith.capstone.whileimout.TaskListActivity.onResume(TaskListActivity.java:58)
10-10 18:55:56.424: E/AndroidRuntime(964):  at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1184)
10-10 18:55:56.424: E/AndroidRuntime(964):  at android.app.Activity.performResume(Activity.java:5082)
10-10 18:55:56.424: E/AndroidRuntime(964):  at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2565)

Answer 1

You are doing your initialization in the constructor; this will not work. You should be doing your initialization in onCreate(). When the constructor is invoked, the context has not been properly initialized.

public class WhileImOut extends Application {

    public static TaskManager taskManager;
    private static Context appContext;

    public void onCreate() {
        super();
        appContext = this;
        initialize();
    }

    public static void initialize() {
        if (taskManager == null && Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
            try{
            File f = appContext.getExternalFilesDir(null); // Exception being thrown here
            taskManager = new TaskManager(f.getAbsolutePath());
            }catch(NullPointerException e){
                Log.d("Bad","NPE");
            }catch(Exception e){

            }
        }
    }
}

(By the way, is there any reason to have a separate initialize() method? If so, is there any reason for it to be public?)