VSMEF011 Both Import and ImportMany applied to same member

A member cannot have both [Import] and [ImportMany] attributes. These attributes are mutually exclusive.

Cause

A property, field, or constructor parameter is decorated with both [Import] and [ImportMany] attributes. MEF cannot determine whether to import a single value or a collection.

Rule description

The [Import] attribute is used to import a single export matching a contract, while [ImportMany] is used to import all exports matching a contract into a collection. Applying both to the same member creates an ambiguous situation that MEF cannot resolve.

Examples of violations

Both attributes on a property

using System.Collections.Generic;
using System.ComponentModel.Composition;

class Service
{
    [Import]
    [ImportMany]
    public IEnumerable<ILogger> Loggers { get; set; }  // ❌ Cannot have both
}

Both attributes on a constructor parameter

using System.Collections.Generic;
using System.ComponentModel.Composition;

[Export]
class Service
{
    [ImportingConstructor]
    public Service(
        [Import]
        [ImportMany]
        ILogger[] loggers)  // ❌ Cannot have both
    {
    }
}

Both attributes on a field

using System.Collections.Generic;
using System.ComponentModel.Composition;

class Service
{
    [Import]
    [ImportMany]
    private IEnumerable<ILogger> loggers;  // ❌ Cannot have both
}

How to fix violations

Option 1: Use Import for a single value

using System.ComponentModel.Composition;

class Service
{
    [Import]
    public ILogger Logger { get; set; }  // ✅ Single import
}

Option 2: Use ImportMany for a collection

using System.Collections.Generic;
using System.ComponentModel.Composition;

class Service
{
    [ImportMany]
    public IEnumerable<ILogger> Loggers { get; set; }  // ✅ Multiple imports
}

When to suppress warnings

This warning should not be suppressed as it indicates code that will fail during part discovery.