Can be used to load data from a Google Play Services API such as FusedLocationProvider or Wearable DataApi

GoogleApiClientLoader.kt

import android.content.Context
import android.os.Bundle
import android.support.v4.content.Loader

import com.google.android.gms.common.ConnectionResult
import com.google.android.gms.common.api.GoogleApiClient

import timber.log.Timber

/**
 * Stores away the application context associated with context.
 * Since Loaders can be used across multiple activities it's dangerous to
 * store the context directly; always use [.getContext] to retrieve
 * the Loader's Context, don't use the constructor argument directly.
 * The Context returned by [.getContext] is safe to use across
 * Activity instances.

 * @param context used to retrieve the application context.
 */
abstract class GoogleApiClientLoader<D>(context: Context) : Loader<D>(context),
        GoogleApiClient.ConnectionCallbacks, GoogleApiClient.OnConnectionFailedListener {

    /**
     * Do not call [GoogleApiClient.disconnect] on this object, except from
     * [GoogleApiClientLoader] class.
     */
    private val mGoogleApiClient: GoogleApiClient

    private var mData: D? = null

    /**
     * @return the connection result if [.mGoogleApiClient] connection failed,
     * * or null otherwise.
     */
    var connectionResult: ConnectionResult? = null
        private set

    init {
        @Suppress("LeakingThis")
        mGoogleApiClient = getNewApiClient(context)
    }

    protected abstract fun getNewApiClient(context: Context): GoogleApiClient
    protected abstract fun startLoadingData(googleApiClient: GoogleApiClient)
    protected abstract fun stopLoading(googleApiClient: GoogleApiClient)
    protected abstract fun onGoogleApiClientDisconnect(googleApiClient: GoogleApiClient)
    protected fun onResult(data: D?) {
        mData = data
        deliverResult(data)
    }

    override fun onStartLoading() {
        if (mData != null) deliverResult(mData)
        if (mGoogleApiClient.isConnected) {
            startLoadingData(mGoogleApiClient)
        } else mGoogleApiClient.connect()
    }

    override fun onStopLoading() {
        if (mGoogleApiClient.isConnected) stopLoading(mGoogleApiClient)
    }

    override fun onForceLoad() {
        if (mData != null) deliverResult(mData)
        if (!mGoogleApiClient.isConnected) mGoogleApiClient.connect()
    }

    override final fun onConnected(connectionHint: Bundle?) {
        connectionResult = null
        if (mData != null) deliverResult(mData)
        startLoadingData(mGoogleApiClient)
    }

    override final fun onConnectionSuspended(cause: Int) {
        Timber.wtf("onConnectionSuspended(cause=%d)", cause)
        deliverResult(null)
    }

    override final fun onConnectionFailed(connectionResult: ConnectionResult) {
        this.connectionResult = connectionResult
        deliverResult(null)
    }

    override fun onReset() {
        if (mGoogleApiClient.isConnected || mGoogleApiClient.isConnecting) {
            onGoogleApiClientDisconnect(mGoogleApiClient)
            mGoogleApiClient.disconnect()
        }
    }
}