dependencies {
         compile 'com.lemon.library:custom-font:1.0.0'
}

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="font">
        <attr name="type">
            <enum name="regular" value="1" />
            <enum name="medium" value="2" />
            <enum name="bold" value="3" />
        </attr>
    </declare-styleable>
</resources>

public class BaseApplication extends Application {
    @Override
    public void onCreate() {
        super.onCreate();

        HashMap<Integer, String> fontTypeMap = new HashMap<>();
        // 1st param = your attrs.xml under declare-styleable attr enum value
        // 2nd param = your assets path
        fontTypeMap.put(1, "fonts/SanFranciscoText-Regular.otf");
        fontTypeMap.put(2, "fonts/SanFranciscoText-Medium.otf");
        fontTypeMap.put(3, "fonts/SanFranciscoText-Bold.otf");
        CustomFontConfiguration customFontConfiguration = new CustomFontConfiguration.Builder()
                .setResourceDeclareStyleableName(R.styleable.font) // your attrs.xml declare-styleable name
                .setResourceAttr(R.styleable.font_type) // your attrs.xml under declare-styleable attr name
                .setFontTypeMap(fontTypeMap)
                .build();
        CustomFontEngine.setConfiguration(customFontConfiguration);

    }
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.lemon.customfont">

    <application
        android:name=".BaseApplication"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

<com.lemon.library.widget.CustomFontTextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="CustomFontTextViewRegular"
        customfont:type="regular" />
        
<com.lemon.library.widget.CustomFontButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="CustomFontButtonRegular"
        customfont:type="regular" />
        
<com.lemon.library.widget.CustomFontEditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="@dimen/activity_vertical_margin"
        android:text="CustomFontEditTextMedium"
        customfont:type="medium" />

LCustomFont library for Android
Copyright (c) 2017 LemonNicholas (http://github.com/LemonNicholas).

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.