Theme and Style customization

public class MainActivity extends AppCompatActivity {

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

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:custom="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <com.customthemeattributedemo.customview.CustomTextView
        style="?mediumTextStyle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="20dp"
        android:text="@string/message_hello"
        custom:font_family="@string/bold_font" />

    <com.customthemeattributedemo.customview.CustomTextView
        style="?largeTextStyle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="20dp"
        android:text="@string/message_hello"
        custom:font_family="@string/bold_font" />
</LinearLayout>

public class CustomTextView extends TextView {

    private static final String TAG = "TextViewPlus";
    private Context mContext;

    public CustomTextView(Context context) {
        super(context);
        mContext = context;
    }

    public CustomTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        mContext = context;
        setCustomFont(context, attrs);
    }

    public CustomTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        mContext = context;
        setCustomFont(context, attrs);
    }

    private void setCustomFont(Context ctx, AttributeSet attrs) {
        TypedArray customFontNameTypedArray = ctx.obtainStyledAttributes(attrs, R.styleable.CustomTextView);
        String customFont = customFontNameTypedArray.getString(R.styleable.CustomTextView_font_family);
        Typeface typeface = null;
        typeface = Typeface.createFromAsset(ctx.getAssets(), customFont);
        setTypeface(typeface);
        customFontNameTypedArray.recycle();
    }
}

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <attr name="mediumTextStyle" format="reference" />
    <attr name="largeTextStyle" format="reference" />

    <declare-styleable name="CustomTextView">

        <attr name="font_family" format="string" />
        <!--- Your other attributes -->

    </declare-styleable>
</resources>

<resources>
    <string name="app_name">Custom Style Theme Attribute Demo</string>
    <string name="message_hello">Hello Hiren!</string>

    <string name="bold_font">bold.ttf</string>
</resources>

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>

        <item name="mediumTextStyle">@style/textMedium</item>
        <item name="largeTextStyle">@style/textLarge</item>
    </style>

    <style name="textMedium" parent="textParentStyle">
        <item name="android:textAppearance">@android:style/TextAppearance.Medium</item>
    </style>

    <style name="textLarge" parent="textParentStyle">
        <item name="android:textAppearance">@android:style/TextAppearance.Large</item>
    </style>

    <style name="textParentStyle">
        <item name="android:textColor">@android:color/white</item>
        <item name="android:background">@color/colorPrimary</item>
        <item name="android:padding">5dp</item>
    </style>

</resources>