Will Toast.makeText cause app crash when I invoke it in asynchronous thread in Android Studio?

The following code is about Google in-app payment based office sample code.

I have to test it in a real mobile phone because it' hard to test Google in-app payment in Android Studio emulator.

Unfortunately, the app crashed in real mobile phone when I open the FragmentBuy, I hardly get the error information about the crash.

I checked my code again and agin, I guest there are two place which cause crash, one is private fun processPurchases(purchasesResult: Set<Purchase>) , another is private fun acknowledgeNonConsumablePurchasesAsync(nonConsumables: List<Purchase>).

1: They lanuch Toast.makeTex in in asynchronous thread, is it reason of crash?

2: Which one is correct between Billing.getInstance(requireActivity(), getString(R.string.skuRegisterApp)) and Billing.getInstance(requireContext), getString(R.string.skuRegisterApp)) ?

3: Is there other problems with my code ?

FragmentBuy.kt

class FragmentBuy : Fragment() {

    private lateinit var binding: LayoutBuyBinding

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        binding = DataBindingUtil.inflate(
            inflater, R.layout.layout_buy, container, false
        )
   
        val mBilling=Billing.getInstance(requireActivity(), getString(R.string.skuRegisterApp)) // or Billing.getInstance(requireContext), getString(R.string.skuRegisterApp))

        mBilling.initBillingClient()

        binding.btnPurchase.setOnClickListener {
           mBilling.purchaseProduct(requireActivity())
        }

        return binding.root
    }

}

fun Context.toast(msg: String){
    Toast.makeText(this, msg, Toast.LENGTH_LONG).show()
}


fun Fragment.toast(@StringRes resId: Int) {
    toast(requireContext().getString(resId))
}

Billing.kt

class Billing private constructor (private val mContext: Context, private val purchaseItem :String)
        :PurchasesUpdatedListener, BillingClientStateListener   {

     private lateinit var playStoreBillingClient: BillingClient
     private val mapSkuDetails = mutableMapOf<String,SkuDetails>()

     fun initBillingClient() {
         playStoreBillingClient = BillingClient
             .newBuilder(mContext)
             .enablePendingPurchases() // required or app will crash
             .setListener(this)
             .build()

         if (!playStoreBillingClient.isReady) {
             playStoreBillingClient.startConnection(this)
         }
     }

    override fun onBillingSetupFinished(billingResult: BillingResult) {
        when (billingResult.responseCode) {
            BillingClient.BillingResponseCode.OK -> {
                querySkuDetailsAsync(BillingClient.SkuType.INAPP, listOf(purchaseItem) )
                queryAndProcessPurchasesAsync()
                mContext.toast(R.string.msgBillINIOK)
            }
            ...
        }
    }

    private fun querySkuDetailsAsync(@BillingClient.SkuType skuType: String, skuList: List<String>) {
        val params = SkuDetailsParams.newBuilder().setSkusList(skuList).setType(skuType).build()
        playStoreBillingClient.querySkuDetailsAsync(params) { billingResult, skuDetailsList ->
            when (billingResult.responseCode) {
                BillingClient.BillingResponseCode.OK -> {
                    if (skuDetailsList.orEmpty().isNotEmpty()) {
                        skuDetailsList?.forEach {
                            mapSkuDetails.put(it.sku,it)
                        }
                    }
                }
                '''
            }
        }
    }

    private fun queryAndProcessPurchasesAsync() {
        val purchasesResult = HashSet<Purchase>()
        var result = playStoreBillingClient.queryPurchases(BillingClient.SkuType.INAPP)
        result?.purchasesList?.apply { purchasesResult.addAll(this) }

        processPurchases(purchasesResult)
    }


    private fun processPurchases(purchasesResult: Set<Purchase>): Job {
        return CoroutineScope(Job() + Dispatchers.IO).launch {
            val validPurchases = HashSet<Purchase>(purchasesResult.size)
            purchasesResult.forEach { purchase ->
                if (purchase.purchaseState == Purchase.PurchaseState.PURCHASED) {
                    if (purchase.sku.equals(purchaseItem)) {
                        if (isSignatureValid(purchase)) {
                            validPurchases.add(purchase)
                            setIsRegisteredAppAsTrue(mContext)
                            mContext.toast(R.string.msgOrderOK)  //Will it be crash?
                        }
                    }
                }
                ...

            }
            acknowledgeNonConsumablePurchasesAsync(validPurchases.toList())
        }
    }


    private fun acknowledgeNonConsumablePurchasesAsync(nonConsumables: List<Purchase>) {
        nonConsumables.forEach { purchase ->
            val params = AcknowledgePurchaseParams.newBuilder()
                           .setPurchaseToken(purchase
                           .purchaseToken).build()

            playStoreBillingClient.acknowledgePurchase(params) { billingResult ->
                when (billingResult.responseCode) {
                    BillingClient.BillingResponseCode.OK -> {
                         mContext.toast(R.string.msgOrderAcknowledgeOK)     //Will it be crash?
                    }
                    else -> mContext.toast(R.string.msgOrderAcknowledgeError, billingResult.debugMessage)
                }
            }
        }
    }



    //执行playStoreBillingClient.launchBillingFlow(...)后 launch
    override fun onPurchasesUpdated(billingResult: BillingResult, purchases: MutableList<Purchase>?) {
        when (billingResult.responseCode) {
            BillingClient.BillingResponseCode.OK -> {
                purchases?.apply { processPurchases(this.toSet()) }
            }
            ...
        }
    }


    fun purchaseProduct(activity: Activity) {
        val skuDetails = mapSkuDetails[purchaseItem]
        skuDetails?.let{
            val purchaseParams = BillingFlowParams.newBuilder().setSkuDetails(skuDetails).build()
            playStoreBillingClient.launchBillingFlow(activity, purchaseParams)
        }
    }


    companion object {
        private const val LOG_TAG = "BillingRepository"

        private var INSTANCE: Billing? = null
        fun getInstance(mContext: Context, purchaseItem: String): Billing =
                     INSTANCE ?: synchronized(this) {
                         INSTANCE ?: Billing(mContext, purchaseItem).also { INSTANCE = it }
                     }
    }


}

1. Yes. You can only show toast messages from the main UI thread. To launch a toask message from any other thread, you can use a Hander like so:

 new Handler(Looper.getMainLooper()).post(() -> {
        Toast.makeText(someContext, "some toast", Toast.LENGTH_SHORT).show();
 });

Also, you have to use activity context, rather than fragment context. To get the activity context from within a fragment, you can use:

getActivity()

So you can do something like this inside your fragment:

 new Handler(Looper.getMainLooper()).post(() -> {
            Toast.makeText(getActivity(), "some toast", Toast.LENGTH_SHORT).show();
 });

Since you are using an extension function, you need to change it to use activity context:

fun Fragment.toast(@StringRes resId: Int) {
    getActivity().toast(requireContext().getString(resId))
}

And then you can use toast() inside your Handler (to show it from a different Thread):

 new Handler(Looper.getMainLooper()).post(() -> {
        toast("some toast")
 });

2. The first one is more correct, but you should use getString() with your activity's context:

   Billing.getInstance(requireActivity(), getActivity().getString(R.string.skuRegisterApp))

3. everything else seems fine