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Android Build a Self-Destructing Message Android App Using Fragments for Tabs Modifying Fragments from the Template

Aalok Patel
Aalok Patel
244 Points

App not running "___" has stopped

When I run the app, I get this error message: (using Android Studio)

10-02 01:42:54.972 1242-1242/com.example.aalok.chirp E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: com.example.aalok.chirp, PID: 1242 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.aalok.chirp/com.example.aalok.chirp.MainActivity}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) at android.app.ActivityThread.access$800(ActivityThread.java:135) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:136) at android.app.ActivityThread.main(ActivityThread.java:5017) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at com.example.aalok.chirp.SectionsPagerAdapter.getPageTitle(SectionsPagerAdapter.java:38) at com.example.aalok.chirp.MainActivity.onCreate(MainActivity.java:94) at android.app.Activity.performCreate(Activity.java:5231) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)             at android.app.ActivityThread.access$800(ActivityThread.java:135)             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)             at android.os.Handler.dispatchMessage(Handler.java:102)             at android.os.Looper.loop(Looper.java:136)             at android.app.ActivityThread.main(ActivityThread.java:5017)             at java.lang.reflect.Method.invokeNative(Native Method)             at java.lang.reflect.Method.invoke(Method.java:515)             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)             at dalvik.system.NativeStart.main(Native Method)

Here is my MainActivity.java package com.example.aalok.chirp;

import java.util.Locale;

import android.app.Activity; import android.app.ActionBar; import android.app.Fragment; import android.app.FragmentManager; import android.app.FragmentTransaction; import android.content.Intent; import android.support.v13.app.FragmentPagerAdapter; import android.os.Bundle; import android.support.v4.view.ViewPager; import android.util.Log; import android.view.Gravity; import android.view.LayoutInflater; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.view.ViewGroup; import android.widget.TextView;

import com.parse.Parse; import com.parse.ParseAnalytics; import com.parse.ParseUser;

import android.support.v4.app.FragmentActivity;

public class MainActivity extends FragmentActivity implements ActionBar.TabListener {

public static final String TAG = MainActivity.class.getSimpleName();

/**
 * The {@link android.support.v4.view.PagerAdapter} that will provide
 * fragments for each of the sections. We use a
 * {@link FragmentPagerAdapter} derivative, which will keep every
 * loaded fragment in memory. If this becomes too memory intensive, it
 * may be best to switch to a
 * {@link android.support.v13.app.FragmentStatePagerAdapter}.
 */
SectionsPagerAdapter mSectionsPagerAdapter;

/**
 * The {@link ViewPager} that will host the section contents.
 */
ViewPager mViewPager;

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

    ParseAnalytics.trackAppOpened(getIntent());

    ParseUser currentUser = ParseUser.getCurrentUser();
    if (currentUser == null) {
        //If user is not logged in, redirect user to Login Screen
        navigateToLogin();
    } else {
        Log.i(TAG, currentUser.getUsername());
    }

    // Set up the action bar.
    final ActionBar actionBar = getActionBar();
    actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

    // Create the adapter that will return a fragment for each of the three
    // primary sections of the activity.
    mSectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mViewPager.setAdapter(mSectionsPagerAdapter);

    // When swiping between different sections, select the corresponding
    // tab. We can also use ActionBar.Tab#select() to do this if we have
    // a reference to the Tab.
    mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
        @Override
        public void onPageSelected(int position) {
            actionBar.setSelectedNavigationItem(position);
        }
    });

    // For each of the sections in the app, add a tab to the action bar.
    for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
        // Create a tab with text corresponding to the page title defined by
        // the adapter. Also specify this Activity object, which implements
        // the TabListener interface, as the callback (listener) for when
        // this tab is selected.
        actionBar.addTab(
                actionBar.newTab()
                        .setText(mSectionsPagerAdapter.getPageTitle(i))
                        .setTabListener(this));
    }
}

private void navigateToLogin() {
    Intent intent = new Intent(this, LoginActivity.class);
    intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
    startActivity(intent);
}


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

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int itemId = item.getItemId();
    if (itemId == R.id.action_logout) {
        ParseUser.logOut();
        navigateToLogin();
    }
    return super.onOptionsItemSelected(item);
}

@Override
public void onTabSelected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
    // When the given tab is selected, switch to the corresponding page in
    // the ViewPager.
    mViewPager.setCurrentItem(tab.getPosition());
}

@Override
public void onTabUnselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}

@Override
public void onTabReselected(ActionBar.Tab tab, FragmentTransaction fragmentTransaction) {
}

}

SectionsPageAdapter.java package com.example.aalok.chirp;

import java.util.Locale; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentPagerAdapter; import android.content.Context;

/**

  • A {@link android.support.v13.app.FragmentPagerAdapter} that returns a fragment corresponding to
  • one of the sections/tabs/pages. */ public class SectionsPagerAdapter extends FragmentPagerAdapter {

    protected Context mContext;

    public SectionsPagerAdapter(Context context, FragmentManager fm) { super(fm); context = mContext; }

    @Override public Fragment getItem(int position) {

    return new InboxFragment();
    

    }

    @Override public int getCount() { return 2; }

    @Override public CharSequence getPageTitle(int position) { Locale l = Locale.getDefault(); switch (position) { case 0: return mContext.getString(R.string.title_section1).toUpperCase(l); case 1: return mContext.getString(R.string.title_section2).toUpperCase(l); } return null; } }

InboxFragment.java package com.example.aalok.chirp;

import android.os.Bundle; import android.support.v4.app.ListFragment; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup;

public class InboxFragment extends ListFragment{

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_inbox, container, false);
    return rootView;
}

}

1 Answer

Nic Huang
PLUS
Nic Huang
Courses Plus Student 10,573 Points

What version of Parse you are using ?? Is it the latest ??