elsa-workflows/elsa-core · error · InvalidOperationException

Method ' ' not found on type ' '.

Error message

Method '{methodName}' not found on type '{HostType.Name}'.

What it means

Thrown by HostMethodActivity.ResolveMethod when the configured method name cannot be found on the HostType using reflection (instance or static, public or non-public). The HostMethod activity executes a named method on a host type, so a missing method name makes execution impossible.

Solutions

1. Correct the MethodName value on the activity to exactly match a method on HostType (name is case-sensitive).
2. Verify HostType is the intended type; fix the activity's Type/HostType configuration if it points at the wrong class.
3. Restore or keep a compatibility method on the host type if existing workflow definitions reference the old name.
4. Consider changing the method from private in a base type to be discoverable, or move lookup to the declaring type.

Example fix

// before
activity.HostType = typeof(OrderService);
activity.MethodName = "ProcessOrder"; // renamed to ProcessAsync

// after
activity.HostType = typeof(OrderService);
activity.MethodName = nameof(OrderService.ProcessAsync);

var flags = BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic;
if (string.IsNullOrWhiteSpace(methodName) || hostType.GetMethod(methodName, flags) is null)
    throw new InvalidOperationException($"Method '{methodName}' does not exist on {hostType.FullName}.");

bool HostHasMethod(Type hostType, string name) => !string.IsNullOrWhiteSpace(name) && hostType.GetMethod(name, BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic) is not null;

try
{
    await hostMethodActivity.ExecuteAsync(context);
}
catch (InvalidOperationException ex) when (ex.Message.Contains("not found on type"))
{
    logger.LogError(ex, "HostMethod '{Method}' missing on {Type}; check workflow definition against current host assembly", methodName, hostType.Name);
}

When it happens

Trigger: Setting the MethodName (workflow property or designer field) to a name that does not exist on HostType, typos or case mismatches, the method being renamed or removed in a newer host assembly, or the overload lookup failing because GetMethod(name) cannot disambiguate multiple overloads (AmbiguousMatchException aside) or the method exists on a base type with different accessibility.

Common situations: Workflows persisted against an older version of the host class that has since been refactored, moving a method to a different class, and renaming methods without updating workflow definitions.

Related errors

• Can't find method name
• Multiple Invoke methods were found. Use either Invoke or…
• Multiple Invoke methods were found. Use either Invoke or…
• No Invoke methods were found. Use either Invoke or…
• No Invoke methods were found. Use either Invoke or…

AI-assisted analysis of elsa-workflows/elsa-core@fe9217bdfa (2026-09-13). Data as JSON: /api/errors/331b2a5ee24fd087. Report an issue: GitHub.

Appendix: source

Thrown at src/modules/Elsa.Workflows.Management/Activities/HostMethod/HostMethodActivity.cs:82

        {
            var callbackMethodName = bookmark.CallbackMethodName;
            
            if (string.IsNullOrWhiteSpace(callbackMethodName))
                continue;
            
            bookmark.CallbackMethodName = nameof(ResumeAsync);
            var metadata = bookmark.Metadata ?? new Dictionary<string, string>();
            
            metadata["HostMethodActivityResumeCallback"] = callbackMethodName;
            bookmark.Metadata = metadata;
        }
    }

    private MethodInfo ResolveMethod(string methodName)
    {
        var method = HostType.GetMethod(methodName, BindingFlags.Instance | BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic);
        if (method == null)
            throw new InvalidOperationException($"Method '{methodName}' not found on type '{HostType.Name}'.");

        return method;
    }

    private async ValueTask<object?[]> BuildArgumentsAsync(MethodInfo method, IReadOnlyCollection<InputDescriptor> inputDescriptors, ActivityExecutionContext context, IServiceProvider serviceProvider, CancellationToken cancellationToken)
    {
        var parameters = method.GetParameters();
        var args = new object?[parameters.Length];

        // Allow multiple providers; call in order.
        var providers = serviceProvider.GetServices<IHostMethodParameterValueProvider>().ToList();
        if (providers.Count == 0)
            providers.Add(new DefaultHostMethodParameterValueProvider());

        for (var i = 0; i < parameters.Length; i++)
        {
            var parameter = parameters[i];

View on GitHub (pinned to fe9217bdfa)