Question

Everything has been working as usual until now: when I click on a button I have clicked a hundred times, suddenly I get a NullPointerException.

This is the relevant code:

View dbButton = findViewById(R.id.db_button);
dbButton.setOnClickListener(this);


public void onClick (View v) {
    switch (v.getId()) {
    case R.id.new_sms_button:
        Intent inte = new Intent(this, NewSMS.class);
        startActivity(inte);
        break;
    case R.id.about_button:
        Intent i = new Intent(this, About.class);
        startActivity(i);
        break;
    case R.id.db_button:
        Intent in = new Intent(this, Profile.class); duplicata
        startActivity(in);
        break;
    case R.id.prefs_button:
        Intent intent1 = new Intent(this, Settings.class);
        startActivity(intent1);
        break;
    }
}

And this is the Profile class:

public class Profile extends Activity {

private UsersData usersData;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.userprofile);

    usersData = new UsersData(this);
    Cursor cursor = getUserData();
    showUserData(cursor);
}

private static String[] FROM = { PHONE_NUMBER, SMS_SENT, SMS_RECEIVED, };
private Cursor getUserData() {
    SQLiteDatabase db = usersData.getReadableDatabase();
    Cursor cursor = db.query(TABLE_NAME, FROM, null, null, null, null, null);
    startManagingCursor(cursor);
    return cursor;
}

private void showUserData(Cursor cursor) {
    StringBuilder builder = new StringBuilder("Data:\n");
    while (cursor.moveToNext()) {
        String num = cursor.getString(0);
        long smss = cursor.getLong(1);
        long smsr = cursor.getLong(2);
        builder.append("num: ").append(num).append("\n");
        builder.append("sent: ").append(smss).append("\n");
        builder.append("received: ").append(smsr).append("\n");
    }
    TextView text = (TextView) findViewById(R.id.userdata);
    text.setText(builder);
}
}

LogCat:

01-10 14:16:56.655: E/AndroidRuntime(2550): FATAL EXCEPTION: main
01-10 14:16:56.655: E/AndroidRuntime(2550): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.app/com.app.Profile}: java.lang.NullPointerException
01-10 14:16:56.655: E/AndroidRuntime(2550):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at android.os.Looper.loop(Looper.java:123)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at android.app.ActivityThread.main(ActivityThread.java:3683)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at java.lang.reflect.Method.invokeNative(Native Method)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at java.lang.reflect.Method.invoke(Method.java:507)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at dalvik.system.NativeStart.main(Native Method)
01-10 14:16:56.655: E/AndroidRuntime(2550): Caused by: java.lang.NullPointerException
01-10 14:16:56.655: E/AndroidRuntime(2550):     at com.rpgsms.Profile.showUserData(Profile.java:78)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at com.rpgsms.Profile.onCreate(Profile.java:50)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
01-10 14:16:56.655: E/AndroidRuntime(2550):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)

UsersData is the app’s database class. Any idea why this is happening?

Answer 1

It’s difficult to tell which statement Profile.java:78 is, but it’s possibly the Cursor parameter being null caused by a failure in db.query(). You need to add more error checking and report them via Log.e().

And incidentally you can simplify your onClick() method rather than creating multiple Intents with different names:

public void onClick (View v) {
    Intent intent = null;
    switch (v.getId()) {
    case R.id.new_sms_button:
        intent = new Intent(this, NewSMS.class);
        break;
    case R.id.about_button:
        intent = new Intent(this, About.class);
        break;
    case R.id.db_button:
        intent = new Intent(this, Profile.class);
        break;
    case R.id.prefs_button:
        intent = new Intent(this, Settings.class);
        break;
    default:
        break;
    }

    if (intent != null) {
        startActivity(intent);
    }
}