Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Android Build a Self-Destructing Message Android App Sending Messages Sending the Message

Posted by Ahmed Fahmy
Ahmed Fahmy
5,295 Points

The App crashes when i try to select a recipient.

Error log:

06-27 11:30:09.989    1949-1949/com.example.fahmy.ribbit E/InputEventReceiver﹕ Exception dispatching input event.
06-27 11:30:09.991    1949-1949/com.example.fahmy.ribbit E/MessageQueue-JNI﹕ Exception in MessageQueue callback: handleReceiveCallback
06-27 11:30:09.994    1949-1949/com.example.fahmy.ribbit E/MessageQueue-JNI﹕ java.lang.NullPointerException: Attempt to invoke interface method 'android.view.MenuItem android.view.MenuItem.setVisible(boolean)' on a null object reference
            at com.example.fahmy.ribbit.RecipientsActivity.onListItemClick(RecipientsActivity.java:138)
            at android.app.ListActivity$2.onItemClick(ListActivity.java:319)
            at android.widget.AdapterView.performItemClick(AdapterView.java:300)
            at android.widget.AbsListView.performItemClick(AbsListView.java:1143)
            at android.widget.AbsListView$PerformClick.run(AbsListView.java:3044)
            at android.widget.AbsListView.onTouchUp(AbsListView.java:3845)
            at android.widget.AbsListView.onTouchEvent(AbsListView.java:3617)
            at android.view.View.dispatchTouchEvent(View.java:8388)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2424)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2158)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2172)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2172)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2172)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2172)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2314)
            at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1692)
            at android.app.Activity.dispatchTouchEvent(Activity.java:2739)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2275)
            at android.view.View.dispatchPointerEvent(View.java:8578)
            at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4021)
            at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3887)
            at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
            at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3502)
            at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3468)
            at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3578)
            at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3476)
            at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3635)
            at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
            at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3502)
            at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3468)
            at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3476)
            at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
            at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5701)
            at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5675)
            at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5646)
            at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5791)
            at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
            at android.os.MessageQueue.nativePollOnce(Native Method)
            at android.os.MessageQueue.next(MessageQueue.java:143)
            at android.os.Looper.loop(Looper.java:122)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
06-27 11:30:09.994    1949-1949/com.example.fahmy.ribbit D/AndroidRuntime﹕ Shutting down VM
06-27 11:30:09.995    1949-1949/com.example.fahmy.ribbit E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.fahmy.ribbit, PID: 1949
    java.lang.NullPointerException: Attempt to invoke interface method 'android.view.MenuItem android.view.MenuItem.setVisible(boolean)' on a null object reference
            at com.example.fahmy.ribbit.RecipientsActivity.onListItemClick(RecipientsActivity.java:138)
            at android.app.ListActivity$2.onItemClick(ListActivity.java:319)
            at android.widget.AdapterView.performItemClick(AdapterView.java:300)
            at android.widget.AbsListView.performItemClick(AbsListView.java:1143)
            at android.widget.AbsListView$PerformClick.run(AbsListView.java:3044)
            at android.widget.AbsListView.onTouchUp(AbsListView.java:3845)
            at android.widget.AbsListView.onTouchEvent(AbsListView.java:3617)
            at android.view.View.dispatchTouchEvent(View.java:8388)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2424)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2158)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2172)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2172)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2172)
            at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2430)
            at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2172)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2314)
            at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1692)
            at android.app.Activity.dispatchTouchEvent(Activity.java:2739)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2275)
            at android.view.View.dispatchPointerEvent(View.java:8578)
            at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4021)
            at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3887)
            at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
            at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3502)
            at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3468)
            at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3578)
            at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3476)
            at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3635)
            at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
            at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3502)
            at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3468)
            at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3476)
            at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3449)
            at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5701)
            at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5675)
            at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5646)
            at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5791)
            at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
            at android.os.MessageQueue.nativePollOnce(Native Method)
            at android.os.MessageQueue.next(MessageQueue.java:143)
            at android.os.Looper.loop(Looper.java:122)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
RecipientsActivity.java 
import android.app.AlertDialog;
import android.app.ListActivity;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.NavUtils;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.Toast;

import com.parse.FindCallback;
import com.parse.ParseException;
import com.parse.ParseFile;
import com.parse.ParseObject;
import com.parse.ParseQuery;
import com.parse.ParseRelation;
import com.parse.ParseUser;
import com.parse.SaveCallback;

import java.util.ArrayList;
import java.util.List;


public class RecipientsActivity extends ListActivity {
    public static final String TAG = RecipientsActivity.class.getSimpleName();

    protected ParseRelation<ParseUser> mFriendsRelation;
    protected ParseUser mCurrentUser;
    protected List<ParseUser> mFriends;
    protected ProgressBar mProgressBar;
    protected MenuItem mSendMenuItem;
    protected Uri mMediaUri;
    protected String mFileType;

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

        getListView().setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);

        mMediaUri = getIntent().getData();
        mFileType = getIntent().getExtras().getString(ParseConstants.KEY_FILE_TYPE);
    }

    @Override
    public void onResume() {
        super.onResume();

        mProgressBar = (ProgressBar) findViewById(R.id.recipientsProgressBar);
        mProgressBar.setVisibility(View.VISIBLE);

        mCurrentUser = ParseUser.getCurrentUser();
        mFriendsRelation = mCurrentUser.getRelation(ParseConstants.KEY_FRIENDS_RELATION);

        ParseQuery<ParseUser> query = mFriendsRelation.getQuery();
        query.orderByAscending(ParseConstants.KEY_USERNAME);
        query.findInBackground(new FindCallback<ParseUser>() {
            @Override
            public void done(List<ParseUser> friends, ParseException e) {
                mProgressBar.setVisibility(View.INVISIBLE);

                if (e == null) {
                    mFriends = friends;
                    String[] usernames = new String[mFriends.size()];
                    int i = 0;
                    for (ParseUser user : mFriends) {
                        usernames[i] = user.getUsername();
                        i++;
                    }
                    ArrayAdapter<String> adapter = new ArrayAdapter<String>(
                            getListView().getContext(),
                            android.R.layout.simple_list_item_checked,
                            usernames);
                    setListAdapter(adapter);
                } else {
                    Log.e(TAG, e.getMessage());
                    AlertDialog.Builder builder = new AlertDialog.Builder(RecipientsActivity.this);
                    builder.setMessage(e.getMessage())
                            .setTitle(getString(R.string.error_title))
                            .setPositiveButton(android.R.string.ok, null);
                    AlertDialog dialog = builder.create();
                    dialog.show();
                }
            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_recipients, menu);
        mSendMenuItem = menu.getItem(0);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        switch (item.getItemId()) {
            case android.R.id.home:
                NavUtils.navigateUpFromSameTask(this);
                return true;
            case R.id.action_send:
                ParseObject message = createMessage();

                if (message == null) {
                    // error
                    AlertDialog.Builder builder = new AlertDialog.Builder(this);
                    builder.setMessage(getString(R.string.error_selecting_file))
                            .setTitle(getString(R.string.error_selecting_file_title))
                            .setPositiveButton(android.R.string.ok, null);
                    AlertDialog dialog = builder.create();
                    dialog.show();
                }
                else {
                    send(message);
                    finish();
                }
                return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        super.onListItemClick(l, v, position, id);

        if (l.getCheckedItemCount() > 0) {
            mSendMenuItem.setVisible(true);
        }
        else {
            mSendMenuItem.setVisible(false);
        }
    }

    protected ParseObject createMessage() {
        ParseObject message = new ParseObject(ParseConstants.CLASS_MESSAGES);
        message.put(ParseConstants.KEY_SENDER_ID, ParseUser.getCurrentUser().getObjectId());
        message.put(ParseConstants.KEY_SENDER_NAME, ParseUser.getCurrentUser().getUsername());
        message.put(ParseConstants.KEY_RECIPIENT_IDS, getRecipientsIds());
        message.put(ParseConstants.KEY_FILE_TYPE, mFileType);

        byte[] fileBytes = FileHelper.getByteArrayFromFile(this, mMediaUri);

        if (fileBytes == null) {
            return null;
        }
        else {
            if (mFileType.equals(ParseConstants.TYPE_IMAGE)) {
                fileBytes = FileHelper.reduceImageForUpload(fileBytes);
            }

            String fileName = FileHelper.getFileName(this, mMediaUri, mFileType);
            ParseFile file = new ParseFile(fileName, fileBytes);
            message.put(ParseConstants.KEY_FILE, file);

            return message;
        }
    }

    protected ArrayList<String> getRecipientsIds() {
        ArrayList<String> recipientsIds = new ArrayList<String>();
        for (int i = 0; i < getListView().getCount(); i++) {
            if (getListView().isItemChecked(i)) {
                recipientsIds.add(mFriends.get(i).getObjectId());
            }
        }
        return recipientsIds;
    }

    protected void send (ParseObject message) {
        message.saveInBackground(new SaveCallback() {
            @Override
            public void done(ParseException e) {
                if (e == null) {
                    // success!
                    Toast.makeText(RecipientsActivity.this,
                            getString(R.string.success_message), Toast.LENGTH_LONG).show();
                }
                else {
                    AlertDialog.Builder builder = new AlertDialog.Builder(RecipientsActivity.this);
                    builder.setMessage(getString(R.string.error_sending_message))
                            .setTitle(getString(R.string.error_selecting_file_title))
                            .setPositiveButton(android.R.string.ok, null);
                    AlertDialog dialog = builder.create();
                    dialog.show();
                }
            }
        });
    }
}
Ahmed Fahmy
Ahmed Fahmy
5,295 Points

When i try to run the app in debug mode it shows the mSendMenuItem equals to null!

3 Answers

Daniel Hartin
Daniel Hartin
18,106 Points
Daniel Hartin
Daniel Hartin
18,106 Points

Hi Ahmed

It looks to me like your variable mSendMenuItem is only set in the method which runs when you inflate the menu but is referenced in your onListItemClicked method which can run without the menu being inflated first which result in the null reference exception you are seeing.

I'm not sure what you're trying to achieve so not sure how to advise but making the menu item visible or invisible seems a little strange to me.

Hope this is of some help Daniel

Ahmed Fahmy
Ahmed Fahmy
5,295 Points
Ahmed Fahmy
Ahmed Fahmy
5,295 Points

Hi Daniel

I found that i forgot to add the theme attribute in my AndroidManifest for the RecipientsActivity, so i fixed it. Thanks for your help :)

Harry James
Harry James
14,780 Points
Harry James
Harry James
14,780 Points

Hey Ahmed!

Glad to hear you got the problem fixed! If you could mark a Best Answer on this post then it'll let other forum users know that the question has been resolved :)

Stefan Indaco
Stefan Indaco
4,245 Points
Stefan Indaco
Stefan Indaco
4,245 Points

I wasn't too clear on the solution so hopefully this helps anyone who runs into this problem. I used android studio targetSDK 23, min 15 At first I removed the setupActionBar() method in the RecipientsActivity because it was causing a nullExceptionPointer error (if you hover over setupActionBar method it warns you about this), this would resolve the problem where when you select a photo, the app would crash. now i can select a photo and move onto the recipients screen where if I select a recipient, I received the same error as in this post's title pointing at the mSendMenuItem having a problem on line 138

"if(list.getCheckedItemCount()>0){mSendMenuItem.setVisible(true);}"

there was no actionbar anymore since I disabled the setup so there was no send button to dropdown from a non-existent menuoptions list I added the theme like ahmed did "@android:style/Theme.Holo.Light.DarkActionBar" to both my recipients.xml under RelativeLayou as well as androidManifest for just the RecipientsActivity.java Activity (one of these I'm assuming can be removed, thinking the one in the recipients.xml file). I added getWindow().requestFeature(Window.FEATURE_ACTION_BAR) in the onCreate method right before the super.onCreate(savedInstanceState); but I feel this can be removed too, haven't tried.