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copied!<p>The default value needs to be specified on the first method called (i.e. your wrapper) as this is where the value is applied to the parameter. <code>Type.Missing</code> is a special value that has meaning in COM interop. Here are some options you could try that may suit your needs.</p> <ol> <li><p>Use the <a href="http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.optionalattribute.aspx" rel="nofollow">OptionalAttibute</a> on the base method and specify the default value on the overridden method.</p> <pre><code>class Class2 : Class1 { public override string MethodWithOptParams(string message = "default message") { return base.MethodWithOptParams(message); } } class Class1 { public virtual string MethodWithOptParams([Optional]string message) { return message; } } </code></pre></li> <li><p>Declare your default values as constants in and apply the same constant as the default value.</p> <pre><code>class Class2 : Class1 { public override string MethodWithOptParams(string message = DefaultMessage) { return base.MethodWithOptParams(message); } } class Class1 { protected const string DefaultMessage = "default message"; public virtual string MethodWithOptParams(string message = DefaultMessage) { return message; } } </code></pre></li> <li><p>Use null as the default value in your wrapper and code the two alternative calls to the base method.</p> <pre><code>class Class2 : Class1 { public override string MethodWithOptParams(string message = null) { if (message == null) { return base.MethodWithOptParams(); } else { return base.MethodWithOptParams(message); } } } class Class1 { public virtual string MethodWithOptParams(string message = "default message") { return message; } } </code></pre></li> </ol>

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