Force closing app when setting the external font

Hi friends,

i have an app with swipe menu and have set a font Roboto font for that in Mainactivity also created a folder in assets and pasted the fonts. But when i run the app it force closes. Please help me.

Mainactivity.java

import java.util.ArrayList;

import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.content.Intent;
import android.content.res.Configuration;
import android.content.res.TypedArray;
import android.graphics.Typeface;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.widget.DrawerLayout;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.TextView;

public class MainActivity extends Activity {
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;

// nav drawer title
private CharSequence mDrawerTitle;

// used to store app title
private CharSequence mTitle;

// slide menu items
private String[] navMenuTitles;
private TypedArray navMenuIcons;

private ArrayList<NavDrawerItem> navDrawerItems;
private NavDrawerListAdapter adapter;

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

    Typeface tf = Typeface.createFromAsset(getAssets(),
            "fonts/Roboto-Regular.ttf");
    TextView tv = (TextView) findViewById(R.id.title);
    tv.setTypeface(tf);


    mTitle = mDrawerTitle = getTitle();

    // load slide menu items
    navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);

    // nav drawer icons from resources
    navMenuIcons = getResources()
            .obtainTypedArray(R.array.nav_drawer_icons);

    mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    mDrawerList = (ListView) findViewById(R.id.list_slidermenu);

    navDrawerItems = new ArrayList<NavDrawerItem>();

    // adding nav drawer items to array
    // Home
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));
    // Find People
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
    // Photos
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[2], navMenuIcons.getResourceId(2, -1)));
    // Communities, Will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[3], navMenuIcons.getResourceId(3, -1)));
    // Pages
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[4], navMenuIcons.getResourceId(4, -1)));
    // What's hot, We  will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[5], navMenuIcons.getResourceId(5, -1)));
    // What's hot, We  will add a counter here
    navDrawerItems.add(new NavDrawerItem(navMenuTitles[6], navMenuIcons.getResourceId(6, -1)));


    // Recycle the typed array
    navMenuIcons.recycle();

    mDrawerList.setOnItemClickListener(new SlideMenuClickListener());

    // setting the nav drawer list adapter
    adapter = new NavDrawerListAdapter(getApplicationContext(),
            navDrawerItems);
    mDrawerList.setAdapter(adapter);

    // enabling action bar app icon and behaving it as toggle button
    getActionBar().setDisplayHomeAsUpEnabled(true);
    getActionBar().setHomeButtonEnabled(true);

    mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
            R.drawable.ic_drawer, //nav menu toggle icon
            R.string.app_name, // nav drawer open - description for accessibility
            R.string.app_name // nav drawer close - description for accessibility
    ) {
        public void onDrawerClosed(View view) {
            getActionBar().setTitle(mTitle);
            // calling onPrepareOptionsMenu() to show action bar icons
            invalidateOptionsMenu();
        }

        public void onDrawerOpened(View drawerView) {
            getActionBar().setTitle(mDrawerTitle);
            // calling onPrepareOptionsMenu() to hide action bar icons
            invalidateOptionsMenu();
        }
    };
    mDrawerLayout.setDrawerListener(mDrawerToggle);

    if (savedInstanceState == null) {
        // on first time display view for first nav item
        displayView(0);
    }
}

/**
 * Slide menu item click listener
 * */
private class SlideMenuClickListener implements
        ListView.OnItemClickListener {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
            long id) {
        // display view for selected nav drawer item
        displayView(position);
    }
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // toggle nav drawer on selecting action bar app icon/title
    if (mDrawerToggle.onOptionsItemSelected(item)) {
        return true;
    }
    // Handle action bar actions click
    switch (item.getItemId()) {
    case R.id.action_settings:
        return true;
    default:
        return super.onOptionsItemSelected(item);
    }
}

/* *
 * Called when invalidateOptionsMenu() is triggered
 */
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
    // if nav drawer is opened, hide the action items
    boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
    menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
    return super.onPrepareOptionsMenu(menu);
}

/**
 * Diplaying fragment view for selected nav drawer list item
 * */
private void displayView(int position) {
    // update the main content by replacing fragments
    Fragment fragment = null;
    switch (position) {
    case 0:
        fragment = new HomeFragment();
        break;
    case 1:
         Intent intent = new Intent(this, Projects.class);
         startActivity(intent);

    break;
    case 2:
        fragment = new Aboutus();
        break;
    case 3:
        fragment = new Services();
        break;
    case 4:
        fragment = new News_events();
        break;
    case 5:
        Intent intent2 = new Intent(this, Gallery.class);
         startActivity(intent2);

    case 6:
        fragment = new Contactus();
        break;

    default:
        break;
    }

    if (fragment != null) {
        FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.frame_container, fragment).commit();

        // update selected item and title, then close the drawer
        mDrawerList.setItemChecked(position, true);
        mDrawerList.setSelection(position);
        setTitle(navMenuTitles[position]);
        mDrawerLayout.closeDrawer(mDrawerList);
    } else {
        // error in creating fragment
        Log.e("MainActivity", "Error in creating fragment");
    }
}

@Override
public void setTitle(CharSequence title) {
    mTitle = title;
    getActionBar().setTitle(mTitle);
}

/**
 * When using the ActionBarDrawerToggle, you must call it during
 * onPostCreate() and onConfigurationChanged()...
 */

@Override
protected void onPostCreate(Bundle savedInstanceState) {
    super.onPostCreate(savedInstanceState);
    // Sync the toggle state after onRestoreInstanceState has occurred.
    mDrawerToggle.syncState();
}

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    // Pass any configuration change to the drawer toggls
    mDrawerToggle.onConfigurationChanged(newConfig);
}

}

Logcat

12-04 07:23:40.905: E/AndroidRuntime(3654): FATAL EXCEPTION: main
12-04 07:23:40.905: E/AndroidRuntime(3654): java.lang.RuntimeException: Unable to start activity ComponentInfo{info.paarva.CrescentBuilders/info.paarva.slidingmenu.MainActivity}: java.lang.NullPointerException
12-04 07:23:40.905: E/AndroidRuntime(3654): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
12-04 07:23:40.905: E/AndroidRuntime(3654): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
12-04 07:23:40.905: E/AndroidRuntime(3654): at android.app.ActivityThread.access$600(ActivityThread.java:141)
12-04 07:23:40.905: E/AndroidRuntime(3654): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
12-04 07:23:40.905: E/AndroidRuntime(3654): at android.os.Handler.dispatchMessage(Handler.java:99)
12-04 07:23:40.905: E/AndroidRuntime(3654): at android.os.Looper.loop(Looper.java:137)
12-04 07:23:40.905: E/AndroidRuntime(3654): at android.app.ActivityThread.main(ActivityThread.java:5103)
12-04 07:23:40.905: E/AndroidRuntime(3654): at java.lang.reflect.Method.invokeNative(Native Method)
12-04 07:23:40.905: E/AndroidRuntime(3654): at java.lang.reflect.Method.invoke(Method.java:525)
12-04 07:23:40.905: E/AndroidRuntime(3654): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
12-04 07:23:40.905: E/AndroidRuntime(3654): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
12-04 07:23:40.905: E/AndroidRuntime(3654): at dalvik.system.NativeStart.main(Native Method)
12-04 07:23:40.905: E/AndroidRuntime(3654): Caused by: java.lang.NullPointerException
12-04 07:23:40.905: E/AndroidRuntime(3654): at info.paarva.slidingmenu.MainActivity.onCreate(MainActivity.java:54)
12-04 07:23:40.905: E/AndroidRuntime(3654): at android.app.Activity.performCreate(Activity.java:5133)
12-04 07:23:40.905: E/AndroidRuntime(3654): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
12-04 07:23:40.905: E/AndroidRuntime(3654): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
12-04 07:23:40.905: E/AndroidRuntime(3654): ... 11 more
12-04 07:23:42.341: I/Process(3654): Sending signal. PID: 3654 SIG: 9