Android Material Design

Basics

The theme is defined in the styles.xml. You have to make sure the minSdkVersion is compatible with the theme. The backward compatible themes without Material Design is

Theme.AppCompat
Theme.AppCompat.Light
Theme.AppCompat.Light.DarkActionBar
Theme.AppCompat.Light.NoActionBar

The equivalent Material Themes are

android.style/Theme.Material
android.style/Theme.Material.Light
android.style/Theme.Material.Light.DarkActionBar
android.style/Theme.Material.Light.NoActionBar

To support older phones we are required to provide a drawable-v21, values-v21 and layout-v21 if we want to be backward compatible.

To implement this we create our styles.xml with a Parent theme which could be thought of as an abstract class.

<resources>
        <!-- Base application theme. -->
        <style name="MaterialTheme" parent="ParentMaterialTheme">
                <!-- Customize your theme here. -->
        </style>

        <style name="ParentMaterialTheme" parent="Theme.AppCompat.Light.NoActionBar">

         <!-- Parent theme For all Pre - lollipop and lollipop above versions i.e. For all devices -->
                <item name="colorPrimary">@color/colorPrimary</item>
                <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
                <item name="colorAccent">@color/colorAccent</item>
        </style>
...

In the styles-v21 in the folder we then have

<?xml version="1.0" encoding="utf-8"?>
<resources>
        <style name="MaterialTheme" parent="ParentMaterialTheme">
                <!-- Customize for only Lollipop and above versions such as Marshmallow device features -->
        </style>
</resources>

Colours

Here are some basic colour pallets for android And for the controls We can find useful guides on https://material.io/design/color/the-color-system.html#color-theme-creation.
Generally you choose these colours.

• Primary
• Primary Dark
• Accent (Secondary Colour)
• Color Control High
• Color Button
• Control Activated

Toolbar

Introduction

• Action Bar can be replaced with Toolbar
• Inherit from ViewGroup and therefore can be placed anywhere
• Compatible with API 7 onwards

Comparability

To keep backward comparability we use the include tag in the activity so they application pick the layout from the appropriate folder.

<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">

        <include
                android:id="@+id/toolbar"
                layout="@layout/toolbar"/>

Theming

We can specify a sub theme for out widgets using the app:theme tag. For example we could have a toolbar.xml with the following.

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.Toolbar
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/colorPrimary"
        android:minHeight="?attr/actionBarSize"
        app:popupTheme="@style/PopupTheme"
        app:theme="@style/ToolBarTheme"/>

The colours for this and it's child components could be define in values/styles.xml

 <style name="ToolBarTheme"  parent="ThemeOverlay.AppCompat.Light">
   <item name="android:textColorPrimary">#FFF</item>    <!-- Text Color of Toolbar Title  -->
   <item name="android:textColorSecondary">#FFF</item>  <!-- Color of Overflow Menu ( 3 DOTS icon )
                                                                    and color of Navigation Drawer Icon-->
 </style>

 <style name="PopupTheme" parent="ThemeOverlay.AppCompat.Light">
     <item name="android:textColorPrimary">@color/grey_500</item>    <!-- Text color of Overflow Menu items-->
     <item name="android:background">@color/overflowMenuBg</item>        <!-- Background of Overflow Menu -->
 </style>

Popup (Overflow) Menu

To Create a popup menu you simply create the layout e.g. res/menu/menu_main.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/edit"
                android:orderInCategory="100"
                android:title="@string/edit"
                app:showAsAction="never"/>
        <item
                android:id="@+id/discard"
                android:icon="@drawable/ic_discard"
                android:orderInCategory="100"
                android:title="@string/delete"
                app:showAsAction="never"/>

...

Override the onOptionsItemSelected

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {

        String msg = "";
        switch (item.getItemId()) {
            case R.id.discard:
                msg = getString(R.string.delete);
                break;
            case R.id.search:
                msg = getString(R.string.search);
                break;
...

Recycler View

This is an improved version of the listview. It provides

• Linear Layout
• Grid Layout
• Staggered Layout

Along with animations

• Delete Item
• Add Item

At the time of writing the required you to make the following gradle changes

...
    compile 'com.android.support:recyclerview-v7:24.1.1'
    compile 'com.android.support:cardview-v7:24.1.1'
...

There appears to be little to do with Material Design in this part of the course but instead a tutorial on creating a recyclerview. I use the one at [[1]]