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POWhy is the indexer on my .NET component not always accessible from VBScript?
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  1. POWhy is the indexer on my .NET component not always accessible from VBScript?
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    copied!<p>I have a .NET assembly which I am accessing from VBScript (classic ASP) via COM interop. One class has an indexer (a.k.a. default property) which I got working from VBScript by adding the following attribute to the indexer: <code>[DispId(0)]</code>. It works in most cases, but not when accessing the class as a member of another object.</p> <p>How can I get it to work with the following syntax: <code>Parent.Member("key")</code> where Member has the indexer (similar to accessing the default property of the built-in <code>Request.QueryString</code>: <code>Request.QueryString("key")</code>)?</p> <p>In my case, there is a parent class <code>TestRequest</code> with a <code>QueryString</code> property which returns an <code>IRequestDictionary</code>, which has the default indexer.</p> <p>VBScript example:</p> <pre><code>Dim testRequest, testQueryString Set testRequest = Server.CreateObject("AspObjects.TestRequest") Set testQueryString = testRequest.QueryString testQueryString("key") = "value" </code></pre> <p>The following line causes an error instead of printing "value". This is the syntax I would like to get working:</p> <pre><code>Response.Write(testRequest.QueryString("key")) </code></pre> <blockquote> <p>Microsoft VBScript runtime (0x800A01C2)<br> Wrong number of arguments or invalid property assignment: 'QueryString'</p> </blockquote> <p>However, the following lines <em>do</em> work without error and output the expected "value" (note that the first line accesses the default indexer on a temporary variable):</p> <pre><code>Response.Write(testQueryString("key")) Response.Write(testRequest.QueryString.Item("key")) </code></pre> <p>Below are the simplified interfaces and classes in C# 2.0. They have been registered via <code>RegAsm.exe /path/to/AspObjects.dll /codebase /tlb</code>:</p> <pre><code>[InterfaceType(ComInterfaceType.InterfaceIsIDispatch)] public interface IRequest { IRequestDictionary QueryString { get; } } [ClassInterface(ClassInterfaceType.None)] public class TestRequest : IRequest { private IRequestDictionary _queryString = new RequestDictionary(); public IRequestDictionary QueryString { get { return _queryString; } } } [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)] public interface IRequestDictionary : IEnumerable { [DispId(0)] object this[object key] { [DispId(0)] get; [DispId(0)] set; } } [ClassInterface(ClassInterfaceType.None)] public class RequestDictionary : IRequestDictionary { private Hashtable _dictionary = new Hashtable(); public object this[object key] { get { return _dictionary[key]; } set { _dictionary[key] = value; } } } </code></pre> <p>I've tried researching and experimenting with various options but have not yet found a solution. Any help would be appreciated to figure out why the <code>testRequest.QueryString("key")</code> syntax is not working and how to get it working.</p> <p>Note: This is a followup to <a href="https://stackoverflow.com/questions/299251/exposing-the-indexer-default-property-via-com-interop">Exposing the indexer / default property via COM Interop</a>.</p> <p>Update: Here is some the generated IDL from the type library (using <a href="http://www.microsoft.com/downloads/details.aspx?familyid=9d467a69-57ff-4ae7-96ee-b18c4790cffd&amp;displaylang=en" rel="nofollow noreferrer">oleview</a>):</p> <pre><code>[ uuid(C6EDF8BC-6C8B-3AB2-92AA-BBF4D29C376E), version(1.0), custom(0F21F359-AB84-41E8-9A78-36D110E6D2F9, AspObjects.IRequest) ] dispinterface IRequest { properties: methods: [id(0x60020000), propget] IRequestDictionary* QueryString(); }; [ uuid(8A494CF3-1D9E-35AE-AFA7-E7B200465426), version(1.0), custom(0F21F359-AB84-41E8-9A78-36D110E6D2F9, AspObjects.IRequestDictionary) ] dispinterface IRequestDictionary { properties: methods: [id(00000000), propget] VARIANT Item([in] VARIANT key); [id(00000000), propputref] void Item( [in] VARIANT key, [in] VARIANT rhs); }; </code></pre>
 

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