## Add the Merchant Library

### Include Dependency
To get started, add the Button Merchant Library to your `build.gradle` file in the dependencies.

```groovy
    implementation 'com.usebutton.merchant:button-merchant:1+'
```

Allow Gradle to download and include the Button Merchant Library before continuing.

### Setup Library
Next, import and configure the Button Merchant Library in either the `Application` subclass (preferred), or in the launching `Activity`.

```kotlin
import com.usebutton.merchant.ButtonMerchant

class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()

// Replace app-xxxxxxxxxxxxxxxx with your App ID from the
        // Button Dashboard: https://app.usebutton.com
        ButtonMerchant.configure(this, "app-xxxxxxxxxxxxxxxx")
    }
}
```

```java
import com.usebutton.merchant.ButtonMerchant;

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

// Replace app-xxxxxxxxxxxxxxxx with your App ID from the
        // Button Dashboard: https://app.usebutton.com
        ButtonMerchant.configure(this, "app-xxxxxxxxxxxxxxxx");
    }
}
```

> 📘
>
> ### Note
> The Button Merchant Library is disabled by default. No user activity is reported and no data is collected until configured with an application id. Initialization can be deferred by simply not calling this method until ready to do so.

Additionally, some users will be initializing your application from a fresh install after following a promotion. In order to fulfill these specific user requests, include a call from within your application’s main `Activity` `onCreate` method to `ButtonMerchant.handlePostInstallIntent`. This will fetch the user’s intent prior to the fresh install, and route them directly to your relevant promotion. The `handlePostInstallIntent` method will pass a non-null url to the listener only once, upon first app launch following an install from a [Button Link](https://developer.usebutton.com/docs/web-app-links).

```kotlin
import com.usebutton.merchant.ButtonMerchant

class MainActivity : Activity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

ButtonMerchant.handlePostInstallIntent(this) { intent, throwable ->
            // If Intent is available, start it
            intent?.let { startActivity(it) }

// Or if an error is provided, handle that
            throwable?.let {
                Log.e("Button", "Error checking post install Intent", it)
            }
        }
    }
}
```

```java
import com.usebutton.merchant.ButtonMerchant;

public class MainActivity extends Activity {
    @Override
    public void onCreate() {
        super.onCreate();

ButtonMerchant.handlePostInstallIntent(this, new PostInstallIntentListener() {
            @Override
            public void onResult(@Nullable Intent intent, @Nullable Throwable t) {
                if (intent != null) {
                    startActivity(intent);
                } else if (t != null) {
                    Log.e(TAG, "Error checking post install Intent", t);
                }
            }
        });
    }
}
```

### Proguard Rules
If your app is using [Proguard](https://developer.android.com/studio/build/shrink-code), make sure it includes rules for the Button Merchant Library. This file is usually located in `yourapp/proguard-rules.pro`, or its location is specified in `build.gradle`, look for `proguardFiles` in your default or variant configuration (note: this can be multiple files).

Here is an example `proguard-rules.pro` snippet including the Button Merchant Library

```undefined
-keepattributes Exceptions,InnerClasses,EnclosingMethod
-keep class com.usebutton.** { *; }
-keepclassmembers class * implements android.os.Parcelable {
    static ** CREATOR;
}
-keep class com.google.android.gms.ads.identifier.AdvertisingIdClient { public *; }
```

## Register Deep Links
Button’s Merchant Library will abstract away any complexities of token management for you, including extracting the token from any incoming deeplinks.
For users that have already installed your application and are entering from another application’s promotion, pass the incoming URL to the Button Merchant Library in order to accurately attribute and handle their intent.

The `ButtonMerchant` class allows you to handle both [Android App Links](https://developer.android.com/training/app-links) and Custom Scheme URLs by passing the user intent to `trackIncomingIntent`.

This method should be called from the `onCreate` method in your launch `Activity` or whichever `Activity` handles incoming links. For example, if you use [Verified App Links](https://developer.android.com/training/app-links/verify-site-associations.html) to directly open the product `Activity`, `ButtonMerchant.trackIncomingIntent` should be called from `ProductActivity.onCreate`.

It is important that `trackIncomingIntent` is called first in the `Activity` that handles incoming links. If the link that opens the app is not a Button Link, the Merchant Library will make this determination and Button will not be a part of the user journey.

```kotlin
import com.usebutton.merchant.ButtonMerchant

class ProductActivity : Activity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

// Handle custom scheme deeplinks and App Links
        ButtonMerchant.trackIncomingIntent(this, intent)
    }
}
```

```java
import com.usebutton.merchant.ButtonMerchant;

public class ProductActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

// Handle custom scheme deeplinks and App Links
        ButtonMerchant.trackIncomingIntent(this, getIntent());
    }
}
```

> 🚧
>
> ### Note
> If your Activity is set to run in a non-standard `launchMode` such as `singleTop`, `singleTask`, or `singleInstance` mode, please make sure to call `ButtonMerchant.trackIncomingIntent(~)` from the `onNewIntent` method in addition to the aforementioned `onCreate`.

## Setup your Button Links domain
Once you’ve registered your Button Links subdomain (`yourdomain.bttn.io`), the last step is to add support for those links via intent filter within your Activity Declaration. If you’ve already registered an intent filter for your domain, you can simply add another to the same Activity Declaration.

We support verified web associated [App Links](http://developer.android.com/training/app-links/index.html#web-assoc) so make sure to add the `autoVerify="true"` attribute to your intent filter.

```xml
<activity name=".MainActivity">
        <!-- Make sure to add this as a NEW Intent Filter in your Activity block -->
        <intent-filter android:autoVerify="true">
                <action android:name="android.intent.action.VIEW"/>
                <category android:name="android.intent.category.DEFAULT"/>
                <category android:name="android.intent.category.BROWSABLE"/>

<data
                    android:host="yourdomain.bttn.io"
                    android:pathPattern=".*"
                    android:scheme="https" />
        </intent-filter>
</activity>
```

Button hosts the Digital Asset Links JSON file for your `bttn.io` subdomain.

- Once you have your updated Android Universal Link, navigate to the [Button Dashboard Apps Section](https://app.usebutton.com//merchant/integration-status/apps) to add your certificate fingerprint.

- Choose your Android application and click its name to drill in.

- Scroll down to the **Configurations** section and select **Add Manual Configuration**. If you've already added one, click **Edit** on the right side of that record.

- You can add your package name and sha256 certificate fingerprints to your app configuration here.

Use the following command to generate the fingerprint via the Java keytool:

```undefined
    keytool -list -printcert -jarfile  <APK_FILE>  | grep SHA256
```

Now, your link should open your app without ever opening your browser when the app is installed.

> 📘
>
> ### Note
> By supporting web associated app links you will prevent the Intent Chooser when opening the URL and your app will open automatically.