Permissions + SumType (https://github.com/madebyatomicrobot/sumtype)

1_DevicePhoneNumber.java

// annotation processor will generate DevicePhoneNumberSumType (see: 4_DevicePhoneNumberSumType.java)
@SumType
public interface DevicePhoneNumber {
    String phoneNumber();
    void phoneNumberNotAvailable();
    String[] permissionsRequired();
}

2_otto.java

// lives on the application, not activity
@Produce
public DevicePhoneNumberSumType produceCurrentPhoneNumber() {
    return buildDevicePhoneNumberSumType();
}

@Subscribe
public void handleGetPhoneNumber(GetDevicePhoneNumber event) {
    bus.post(buildDevicePhoneNumber());
}

private DevicePhoneNumberSumType buildDevicePhoneNumber() {
    String[] permissionsRequired = { android.Manifest.permission.READ_PHONE_STATE };
    if (PermissionUtil.checkPermissionsGranted(application, permissionsRequired)) {
        TelephonyManager phoneManager = (TelephonyManager) application.getSystemService(Context.TELEPHONY_SERVICE);
        String phoneNumber = phoneManager.getLine1Number();
        if (!TextUtils.isEmpty(phoneNumber)) {
            return DevicePhoneNumberSumType.ofPhoneNumber(phoneNumber);
        } else {
            return DevicePhoneNumberSumType.ofPhoneNumberNotAvailable();
        }
    } else {
        return DevicePhoneNumberSumType.ofPermissionsRequired(permissionsRequired);
    }
}

3_usage.java

// subscriber lives on the activity
@Subscribe
public void handleDevicePhoneNumber(DevicePhoneNumberSumType devicePhoneNumber) {
    devicePhoneNumber.accept(new DevicePhoneNumberSumTypeVisitor() {
            @Override
            public void visitPhoneNumber(String phoneNumber) {
                // Display the phone number
            }

            @Override
            public void visitPhoneNumberNotAvailable() {

            }

            @Override
            public void visitPermissionsRequired(String[] permissionsRequired) {
                // Request permissions
            }
        });
}

4_generated.java

// HERE FOR REFERENCE ONLY - GENERATED AT COMPILE TIME BY ANNOTATION PROCESSOR

import java.lang.IllegalStateException;
import java.lang.Object;
import java.lang.Override;
import java.lang.String;

/**
 * Generated sum type class for {@link DevicePhoneNumber} */
public final class DevicePhoneNumberSumType implements DevicePhoneNumber {
  private static final Object voidPlaceholder = new Object();

  private final String phoneNumber;

  private final Object phoneNumberNotAvailable;

  private final String[] permissionsRequired;

  private DevicePhoneNumberSumType(String phoneNumber, Object phoneNumberNotAvailable, String[] permissionsRequired) {
    this.phoneNumber = phoneNumber;
    this.phoneNumberNotAvailable = phoneNumberNotAvailable;
    this.permissionsRequired = permissionsRequired;
  }

  public static DevicePhoneNumberSumType ofPhoneNumber(String phoneNumber) {
    if (phoneNumber == null) {
      throw new IllegalArgumentException();
    }
    return new DevicePhoneNumberSumType(phoneNumber, null, null);
  }

  @Override
  public String phoneNumber() {
    if (phoneNumber == null) {
      throw new IllegalStateException();
    }
    return phoneNumber;
  }

  public static DevicePhoneNumberSumType ofPhoneNumberNotAvailable() {
    return new DevicePhoneNumberSumType(null, voidPlaceholder, null);
  }

  @Override
  public void phoneNumberNotAvailable() {
    if (phoneNumberNotAvailable == null) {
      throw new IllegalStateException();
    }
  }

  public static DevicePhoneNumberSumType ofPermissionsRequired(String[] permissionsRequired) {
    if (permissionsRequired == null) {
      throw new IllegalArgumentException();
    }
    return new DevicePhoneNumberSumType(null, null, permissionsRequired);
  }

  @Override
  public String[] permissionsRequired() {
    if (permissionsRequired == null) {
      throw new IllegalStateException();
    }
    return permissionsRequired;
  }

  public void accept(DevicePhoneNumberSumTypeVisitor visitor) {
    if (phoneNumber != null) {
      visitor.visitPhoneNumber(phoneNumber);
      return;
    }
    if (phoneNumberNotAvailable != null) {
      visitor.visitPhoneNumberNotAvailable();
      return;
    }
    if (permissionsRequired != null) {
      visitor.visitPermissionsRequired(permissionsRequired);
      return;
    }
  }

  public interface DevicePhoneNumberSumTypeVisitor {
    void visitPhoneNumber(String phoneNumber);

    void visitPhoneNumberNotAvailable();

    void visitPermissionsRequired(String[] permissionsRequired);
  }
}

5_PermissionUtil.java

import android.content.Context;
import android.support.v4.content.ContextCompat;

import static android.content.pm.PackageManager.PERMISSION_GRANTED;

public class PermissionUtil {
    public static boolean checkPermissionsGranted(Context context, String...permissions) {
        for (String permission : permissions) {
            if (ContextCompat.checkSelfPermission(context, permission) != PERMISSION_GRANTED) {
                return false;
            }
        }

        return true;
    }
}