title: Android drawer layout not showing
body: <p>I am new to android development. I am trying to implement a drawer layout  there isn't error in the build but the drawer hamburger icon doesn't show.
  here is my xml layout</p>
  
  <pre><code> &lt;LinearLayout
          xmlns:android="http://schemas.android.com/apk/res/android"
          xmlns:tools="http://schemas.android.com/tools"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:orientation="vertical"
          tools:context=".MainActivity"&gt;
  
          &lt;android.support.v7.widget.Toolbar
              android:id="@+id/toolbar"
              android:layout_height="wrap_content"
              android:layout_width="match_parent"
              android:background="?attr/colorPrimary"
              android:minHeight="?android:attr/actionBarSize"
              /&gt;
  
          &lt;android.support.v4.widget.DrawerLayout
              android:id="@+id/drawer_layout"
              android:layout_width="match_parent"
              android:layout_height="match_parent"&gt;
  
              &lt;TextView
                  android:id="@+id/drawer"
                  android:text="@string/hello_world"
                  android:layout_width="wrap_content"
                  android:layout_height="wrap_content" /&gt;
  
              &lt;ListView android:layout_width="240dp"
                  android:layout_height="match_parent"
                  android:layout_gravity="start"
                  /&gt;
  
          &lt;/android.support.v4.widget.DrawerLayout&gt;
  
      &lt;/LinearLayout&gt;
  </code></pre>
  
  <p><strong>MainActivity.java</strong></p>
  
  <pre><code>package com.example.arslan.tutsplus02;
  
  import android.content.res.Configuration;
  import android.support.v4.widget.DrawerLayout;
  import android.support.v7.app.ActionBarDrawerToggle;
  import android.support.v7.app.AppCompatActivity;
  import android.os.Bundle;
  import android.view.Menu;
  import android.view.MenuItem;
  import android.support.v7.widget.Toolbar;
  import android.view.View;
  
  public class MainActivity extends AppCompatActivity {
  
      private DrawerLayout mDrawerLayout;
      private ActionBarDrawerToggle mActionBarDrawerToggle;
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
          setSupportActionBar(toolbar);
  
          getSupportActionBar().setDisplayShowHomeEnabled(true);
          getSupportActionBar().setHomeButtonEnabled(true);
  
          mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
          mActionBarDrawerToggle = new ActionBarDrawerToggle(this,mDrawerLayout,R.string.drawer_opened,R.string.drawer_closed)
          {
              @Override
              public void onDrawerOpened(View drawerView) {
                  if (getSupportActionBar()!= null ) {
                      getSupportActionBar().setTitle(R.string.drawer_opened);
                  }
              }
  
              @Override
              public void onDrawerClosed(View drawerView) {
                  super.onDrawerClosed(drawerView);
                  if (getSupportActionBar()!= null ) {
                      getSupportActionBar().setTitle(R.string.drawer_closed);
                  }
              }
          };
          mDrawerLayout.setDrawerListener(mActionBarDrawerToggle);
      }
  
      @Override
      protected void onPostCreate(Bundle savedInstanceState) {
          super.onPostCreate(savedInstanceState);
          mActionBarDrawerToggle.syncState();
  
      }
  
      @Override
      public void onConfigurationChanged(Configuration newConfig) {
          super.onConfigurationChanged(newConfig);
          mActionBarDrawerToggle.onConfigurationChanged(newConfig);
      }
  
      @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_main, menu);
          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.
          int id = item.getItemId();
  
          if (mActionBarDrawerToggle.onOptionsItemSelected(item))
          {
              return true;
          }
  
          //noinspection SimplifiableIfStatement
          if (id == R.id.action_settings) {
              return true;
          }
  
          return super.onOptionsItemSelected(item);
      }
  }
  </code></pre>
  
  <p>Thanks</p>