CA2216: Disposable types should declare finalizer

Cause

A type that implements System.IDisposable, and has fields that suggest the use of unmanaged resources, does not implement a finalizer as described by Object.Finalize.

Rule Description

A violation of this rule is reported if the disposable type contains fields of the following types:

• System.IntPtr

• System.UIntPtr

• System.Runtime.InteropServices.HandleRef

How to Fix Violations

To fix a violation of this rule, implement a finalizer that calls your Dispose method.

When to Suppress Warnings

It is safe to suppress a warning from this rule if the type does not implement IDisposable for the purpose of releasing unmanaged resources.

Example

The following example shows a type that violates this rule.

using System;  
using System.Runtime.InteropServices;

namespace UsageLibrary
{
    public class  DisposeMissingFinalize :IDisposable
    {
        private bool disposed = false;
        private IntPtr unmanagedResource;

        [DllImport("native.dll")]
        private static extern IntPtr AllocateUnmanagedResource();

        [DllImport("native.dll")]
        private static extern void FreeUnmanagedResource(IntPtr p);

        DisposeMissingFinalize()
        {
            unmanagedResource = AllocateUnmanagedResource();
        }

        protected virtual void Dispose(bool disposing) 
        {
            if (!disposed) 
            {
                // Dispose of resources held by this instance.
                FreeUnmanagedResource(unmanagedResource);
                disposed = true;

                // Suppress finalization of this disposed instance.
                if (disposing)
                {
                    GC.SuppressFinalize(this);
                }
            }
        }

        public void Dispose()
        {
            Dispose(true);
        }

        // Disposable types with unmanaged resources implement a finalizer.
        // Uncomment the following code to satisfy rule:
        //  DisposableTypesShouldDeclareFinalizer
        // ~TypeA()
        // {
        //     Dispose(false);
        // }
    }
}

Related Rules

CA2115: Call GC.KeepAlive when using native resources

CA1816: Call GC.SuppressFinalize correctly

CA1049: Types that own native resources should be disposable

See Also

Reference

Implementing Finalize and Dispose to Clean Up Unmanaged Resources

System.IDisposable

System.IntPtr

System.Runtime.InteropServices.HandleRef

System.UIntPtr

Object.Finalize