Fix BillingResult ObjectDisposedException in Billing 8.0.0.1

[Copilot]

This PR fixes an ObjectDisposedException that occurs when accessing BillingResult.ResponseCode after calling QueryProductDetailsAsync in the Billing Client 8.0.0.1 binding.

Problem

Users reported crashes when trying to access ResponseCode from the result of QueryProductDetailsAsync:

var productList = new[] { QueryProductDetailsParams.Product.NewBuilder().SetProductId(sku).SetProductType(productType).Build() };
var _params = QueryProductDetailsParams.NewBuilder().SetProductList(productList).Build();
var returnValue = await billingClient.QueryProductDetailsAsync(_params);
if (returnValue.Result.ResponseCode == BillingResponseCode.Ok) { ... } // crashes here

The exception occurred because the native Java BillingResult objects were being disposed after callback completion, but the C# wrappers still held references to them:

System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'Android.BillingClient.Api.BillingResult'.
   at Java.Interop.JniPeerMembers.AssertSelf(IJavaPeerable self)
   at Android.BillingClient.Api.BillingResult.get_ResponseCode()

Solution

Modified all internal response listeners in source/com.android.billingclient/billing/Additions/Additions.cs to create persistent copies of BillingResult objects using the Builder pattern. Instead of passing the original BillingResult reference (which may be disposed by the native side), we now create new instances with the same data:

var resultCopy = BillingResult.NewBuilder()
    .SetResponseCode((int)result.ResponseCode)
    .SetDebugMessage(result.DebugMessage)
    .SetOnPurchasesUpdatedSubResponseCode(result.OnPurchasesUpdatedSubResponseCode)
    .Build();

This ensures the managed objects have persistent Java references that won't be disposed unexpectedly.

Files Changed

• Fixed InternalProductDetailsResponseListener (primary fix for the reported issue)
• Fixed InternalAcknowledgePurchaseResponseListener
• Fixed InternalBillingClientStateListener
• Fixed InternalConsumeResponseListener
• Fixed InternalPriceChangeConfirmationListener
• Fixed InternalPurchaseHistoryResponseListener
• Fixed InternalPurchasesUpdatedListener

The same issue did not occur in version 7.1.1.4, indicating this is a regression introduced in the 8.0.0 upgrade.

Fixes #1231.

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[jonathanpeppers]

This is not the appropriate fix.

1. Undo all your changes

2. Next, let's maybe take this approach instead:

        public async Task<QueryPurchasesResult> QueryPurchasesAsync(QueryPurchasesParams purchasesParams)
        {
            var tcs = new TaskCompletionSource<QueryPurchasesResult>();

            var listener = new InternalPurchasesResponseListener
            {
                PurchasesResponseHandler = (r, s) => tcs.TrySetResult(new QueryPurchasesResult
                {
                    Result = r,
                    Purchases = s
                })
            };

            QueryPurchases(purchasesParams, listener);

            var result = await tcs.Task;
            GC.KeepAlive (listener);
            return result;
        }

3. Apply this change to all places needed in source/com.android.billingclient/billing/Additions/Additions.cs.

[Copilot]

This is not the appropriate fix.

1. Undo all your changes
   ...

I've implemented the requested changes:

1. ✅ Undid all previous changes by reverting to the original file state
2. ✅ Applied the GC.KeepAlive approach to all async methods in BillingClient:
   • AcknowledgePurchaseAsync
   • ConsumeAsync
   • QueryProductDetailsAsync
   • QueryPurchasesAsync
   • StartConnectionAsync

Each method now uses async/await pattern with GC.KeepAlive(listener) to prevent the listener from being garbage collected before the native callback completes. This should resolve the ObjectDisposedException without creating unnecessary BillingResult copies.

Fixed in commit e3ae4b3.

[jonathanpeppers]

@tipa I think this is plausible that it could fix the ObjectDisposedException, but it seems like the old version would have had a similar issue.

The version number is unchanged, because we didn't ship it yet:

• Xamarin.Android.Google.BillingClient.8.0.0.1.nupkg.zip

[tipa]

@jonathanpeppers the problem persists - I will send you an example project for you to reproruce the crash

[jonathanpeppers]

/azp run

[azure-pipelines]

Azure Pipelines could not run because the pipeline triggers exclude this branch/path.

[jonathanpeppers]

The .nupkg here can be tested with:

• https://github.com/dotnet/maui-samples/blob/3404ccbab7a3a1ca2dc55d6f426b614aba6cdda2/10.0/BillingService/BillingService/BillingService.csproj#L60

I believe it currently hits a build error with r8.jar.