同时加载多个广告

suspend fun prepare(format: AdFormat): VideoAd? = try {
    ads.format(format).also {
        it.load()
        it.listener = this
    }
} catch (e: VideoAdException) {
    null                                   // 这次该格式无填充
}

lifecycleScope.launch {
    val overlay = async { prepare(AdFormat.OVERLAY) }
    val pause = async { prepare(AdFormat.PAUSE) }
    val linear = async { prepare(AdFormat.LINEAR) }
    overlayAd = overlay.await()
    pauseAd = pause.await()
    linearAd = linear.await()
}