Material design is a set of rule built by Google that guide how to develop an Android app. They can be applied not only to Android apps but also to web design. In the process of developing an app, Android provides some libraries that help developers to implement the main material guide line rules. The most important libraries are:

• com.android.support:appcompat-v7:23.1.0
• com.android.support:design:23.1.0

After all, these two libraries are imported by default when a developer starts a new project using Android Studio.

One important aspect of an app is represented by the color schema. Material design rules describe how to chose colors.

Let us suppose we create a simple Android project and let us follow the steps to implement an Android app following Material design rules.

Material Design: Colors

The first step is choosing the color schema for our app. For this purpose there is a great website that can be used to create the color schema according to material design rules.

After the colors are selected we can download colors.xml:

<resources>
    <color name="primary">#3F51B5</color>
    <color name="primary_dark">#303F9F</color>
    <color name="primary_light">#C5CAE9</color>
    <color name="accent">#03A9F4</color>
    <color name="primary_text">#212121</color>
    <color name="secondary_text">#727272</color>
    <color name="icons">#FFFFFF</color>
    <color name="divider">#B6B6B6</color>
</resources>

You can select the schema you like. The first result is shown in the picture below: 

Now it's time to create our theme that uses the colors we selected before. The app should support the largest number of smart phones—not only those running Lollipop or later.

For this reason it is necessary to create two themes: one for the devices that run Android 5 or later and those that run pre-lollipop version.

So let's create two directories under the values:

style

style-v21

The first one is used by all smart phones running pre-Lollipop versions while the second folder is used by smart phones with OS starting from Lollipop.

In the first directory, style.xml we do:

<resources>
    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">    <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/primary&lt/item>
        <item name="colorPrimaryDark">@color/primary_dark</item>
        <item name="colorAccent">@color/accent</item>
    </style>
    <style name="MyAppTheme" parent="@style/AppTheme" />
</resources>

While in the second directory we simply add:

<resources>
   <style name="MyAppTheme" parent="AppTheme">
     <item name="android:windowContentTransitions">true</item>
     <item name="android:windowAllowEnterTransitionOverlap">true</item>
     <item name="android:windowAllowReturnTransitionOverlap">true</item>
     <item name="android:windowSharedElementEnterTransition">@android:transition/move</item>
     <item name="android:windowSharedElementExitTransition">@android:transition/move</item>
  </style>
</resources>

Finally, in Manifest.xml, modify the file like so:

<application
     android:theme="@style/MyAppTheme" >
     ...
</application>

Android Toolbar

One of the most important components in developing an Android app is the Toolbar. The toolbar plays the role that was played before by Android's action bar. The toolbar can be used to hold:

• Navigation button
• App tile and subtitle
• Action menu
• Brand logo

According to material design the Toolbar has the primary color we selected before. Add it to the Android app:

<RelativeLayout 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"
    tools:context=".MainActivity"
    android:id="@+id/layout">

   <include layout="@layout/toolbar" />

</RelativeLayout>

Where the toolbar layout is: 

<android.support.v7.widget.Toolbar xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:local="http://schemas.android.com/apk/res-auto"
    android:id="@+id/toolbar"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    android:background="@color/primary"
    local:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
    local:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

Notice at line 5 we set the default height of the toolbar using ?attr/actionBarSize and at line 6 the toolbar background.

In the activity it is necessary to set the toolbar:

@Override
protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
   setToolBar();
}
...
private void setToolBar() {
    Toolbar tb = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(tb);
    ActionBar ab = getSupportActionBar();
    ab.setHomeAsUpIndicator(R.drawable.ic_menu_white_24dp);
    ab.setDisplayHomeAsUpEnabled(true);
}

Running the example we get:

Add Action Menu To Toolbar

Once the toolbar is configured correctly, it is possible to add the action menu or menu items that appear on the Toolbar. To do it, under res/menu add a file called main_menu.xml:

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <item android:id="@+id/menu_settings"
          android:title="Settings"
          android:icon="@android:drawable/ic_menu_preferences"
          app:showAsAction="always"
          android:orderInCategory="100"/>

    <item android:id="@+id/menu_help"
        android:title="Help"
        android:icon="@android:drawable/ic_menu_help"
        app:showAsAction="ifRoom"
        android:orderInCategory="110" />

    <item android:id="@+id/menu_compass"
        android:title="Compass"
        android:icon="@android:drawable/ic_menu_compass"
        app:showAsAction="never"
        android:orderInCategory="105"/>

</menu>

Now in the activity there is:

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

Running the example the app looks like: 

When the user selects one of these item the app should be detect it and take the right action, to do so it is necessary to override a method: 

@Override
public boolean onOptionsItemSelected(MenuItem item) {
   int itemId = item.getItemId();
   String btnName = null;

   switch(itemId) {
     case R.id.menu_settings:
        btnName = "Settings";
        break;
     case R.id.menu_compass:
        btnName = "Compass";
        break;
    case R.id.menu_help:
        btnName = "Help";
        break;

  }

  Snackbar.make(layout, "Button " + btnName, Snackbar.LENGTH_SHORT).show();
  return true;
}

In this case we simply show an info message using a Snackbar. 

Android Navigation Drawer

Navigation drawer is one of the most import UI pattern introduced by Google in developing Android apps. Navigation drawer is a side menu that helps to organize the navigation inside the app. It is a uniform way to access different pages and information inside the app. You can refer to the official Google page to learn more. The implementation is very easy. The custom view that represents the navigation drawer must be the first element in the layout: 

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.DrawerLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/drawer_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".MainActivity"
  >

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <include layout="@layout/toolbar" />

        <!-- Let's add fragment -->
        <FrameLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:id="@+id/frame"/>

    </LinearLayout>



    <android.support.design.widget.NavigationView
        android:id="@+id/navigation"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start"
        app:menu="@menu/nav_items" />


</android.support.v4.widget.DrawerLayout>

In this case the toolbar is inside a LinearLayout, but the way the app handles it is the same shown before. In this case there is a FrameLayout to hold the page content shown through fragments. The NavigationView is the "real" menu of our app. The menu items are written in nav_items.

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <group android:checkableBehavior="single">
        <item android:id="@+id/fab"
              android:title="Floating Action Button"
              android:icon="@drawable/ic_action_fab" />

        <item android:id="@+id/star"
            android:title="Star"
            android:icon="@drawable/ic_action_star" />

        <item android:id="@+id/uploadr"
            android:title="Star"
            android:icon="@drawable/ic_action_upload" />
    </group>
</menu>

To handle when a user clicks on an item is very easy, just write:

private void setNavigationDrawer() {
    dLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
    NavigationView navView = (NavigationView) findViewById(R.id.navigation);
    navView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(MenuItem menuItem) {

            Fragment frag = null;
            int itemId = menuItem.getItemId();

            if (itemId == R.id.fab) {
               frag = new Fragment1();
            }
            else if (itemId == R.id.star) {
                frag = new Fragment2();
            }

            if (frag != null) {
                FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

                transaction.replace(R.id.frame, frag);
                transaction.commit();
                dLayout.closeDrawers();
                return true;
            }

            return false;
        }
    });
}

We simply add a listener to know when one of the menu items is pressed by the user and then set the right fragment. The last step is opening the drawer when the user clicks on the home icon, to do it:

@Override
public boolean onOptionsItemSelected(MenuItem item) {
     int itemId = item.getItemId();
     String btnName = null;

     switch(itemId) {
         ...
         // Android home
         case android.R.id.home: {
             dLayout.openDrawer(GravityCompat.START);
             return true;
         }
     }
   .....
 }

Running the example app we have:

At the end of this post, you know how to use Android navigation drawer and toolbar according to material design guide lines