The Phone Number Hint API, a library powered by [Google Play services](https://developers.google.com/android),
provides a frictionless way to show a user's (SIM-based) phone numbers as a
hint.

The benefits to using Phone Number Hint include the following:

- No additional permission requests are needed
- Eliminates the need for the user to manually type in the phone number
- No Google Account is needed
- Not directly tied to sign-in or sign-up workflows
- Wider support for Android versions compared to Autofill

## How it works

The Phone Number Hint API utilizes a [`PendingIntent`](https://developer.android.com/reference/android/app/PendingIntent.md.txt)
to initiate the flow. Once the PendingIntent has been launched the user will be
presented with a UI, listing out all (SIM-based) phone numbers. The user can
then choose to select a phone number they would like to use or cancel the flow.
The selected phone number will then be made available to the developer to
retrieve from the [`Intent`](https://developer.android.com/reference/android/content/Intent.md.txt).
![Phone Number Hint UI and Settings.](https://developer.android.com/static/identity/phone-number-hint/images/phone_number_hint_ui.png) **Figure 1.** Phone Number Hint UI and Settings

To prepare your app, complete the steps in the following sections.

## Configure your app

Add the [Google Play services](https://developers.google.com/android)
dependency for the Phone Number Hint API to your
[module's Gradle build file](https://developer.android.com/studio/build#module-level),
which is commonly `app/build.gradle`:

```groovy
  apply plugin: 'com.android.application'

  ...

  dependencies {
    implementation 'com.google.android.gms:play-services-auth:22.0.0'
  }
```

### Create a GetPhoneNumbeHintIntentRequest object

Start by creating a [`GetPhoneNumberHintIntentRequest`](https://developers.google.com/android/reference/com/google/android/gms/auth/api/identity/GetPhoneNumberHintIntentRequest) object using the
provided [`GetPhoneNumberHintIntentRequest.Builder()`](https://developers.google.com/android/reference/com/google/android/gms/auth/api/identity/GetPhoneNumberHintIntentRequest.Builder)
method. This request object can then be used to get an `Intent` to start the
Phone Number Hint flow.

### Kotlin

```kotlin
val request: GetPhoneNumberHintIntentRequest = GetPhoneNumberHintIntentRequest.builder().build()
```

### Java

```java
GetPhoneNumberHintIntentRequest request = GetPhoneNumberHintIntentRequest.builder().build();
```

### Requesting Phone Number Hint

Call [`SignInClient.getPhoneNumberHintIntent()`](https://developers.google.com/android/reference/com/google/android/gms/auth/api/identity/SignInClient#getPhoneNumberHintIntent(com.google.android.gms.auth.api.identity.GetPhoneNumberHintIntentRequest)),
passing in the previous `GetPhoneNumberHintIntentRequest` object,
to retrieve the `PendingIntent` to initiate the Phone Number Hint flow.

### Kotlin

```kotlin
val phoneNumberHintIntentResultLauncher = ...

Identity.getSignInClient(activity)
  .getPhoneNumberHintIntent(request)
  .addOnSuccessListener { result: PendingIntent ->
    try {
      phoneNumberHintIntentResultLauncher.launch(
        IntentSenderRequest.Builder(result).build()
      )
    } catch (e: Exception) {
        Log.e(TAG, "Launching the PendingIntent failed")
    }
  }
  .addOnFailureListener {
      Log.e(TAG, "Phone Number Hint failed")
  }
```

### Java

```java
ActivityResultLauncher<Intent> phoneNumberHintIntentResultLauncher = ...

Identity.getSignInClient(activity)
    .getPhoneNumberHintIntent(request)
    .addOnSuccessListener( result -> {
        try {
            phoneNumberHintIntentResultLauncher.launch(result.getIntentSender());
        } catch(Exception e) {
            Log.e(TAG, "Launching the PendingIntent failed", e);
        }
    })
    .addOnFailureListener(e -> {
        Log.e(TAG, "Phone Number Hint failed", e);
    });
```

### Retrieving the phone number

Pass in the `Intent` to [`SignInClient.getPhoneNumberFromIntent`](https://developers.google.com/android/reference/com/google/android/gms/auth/api/identity/SignInClient#getPhoneNumberFromIntent(android.content.Intent))
to retrieve the phone number.

### Kotlin

```kotlin
val phoneNumberHintIntentResultLauncher =
  registerForActivityResult(ActivityResultContracts.StartIntentSenderForResult()) { result ->
        try {
            val phoneNumber = Identity.getSignInClient(activity).getPhoneNumberFromIntent(result.data)
        } catch(e: Exception) {
            Log.e(TAG, "Phone Number Hint failed")
        }
    }
```

### Java

```java
ActivityResultLauncher<Intent> phoneNumberHintIntentResultLauncher =
    registerForActivityResult(
        new ActivityResultContracts.StartActivityForResult(),
        new ActivityResultCallback<ActivityResult>() {
            @Override
            public void onActivityResult(ActivityResult result) {
                try {
                    String phoneNumber = Identity.getSignInClient(activity).getPhoneNumberFromIntent(result.getData());
                } catch {
                    Log.e(TAG, "Phone Number Hint failed", e);
                }
            }
    });
```