Exposing the indexer / default property via COM Interop
I am attempting to write a component in C# to be consumed by classic ASP that allows me to access the indexer of the component (aka default property).
For example:
C# component:
public class MyCollection {
public string this[string key] {
get { /* return the value associated with key */ }
}
public void Add(string key, string value) {
/* add a new element */
}
}
ASP consumer:
Dim collection
Set collection = Server.CreateObject("MyCollection ")
Call collection.Add("key", "value")
Response.Write(collection("key")) ' should print "value"
Is there an attribute I need to set, do I need to implement an interface or do I need to do something else? Or this not possible via COM Interop?
The purpose is that I am attempting to create test doubles for some of the built-in ASP objects such as Request, which make use of collections using these default properties (such as Request.QueryString("key") ). Alternative suggestions are welcome.
Update: I asked a follow-up question: Why is the indexer on my .NET component not always accessible from VBScript?
尝试将属性的DispId属性设置为0，如此处在MSDN文档中所述。
Here is a better solution that uses an indexer rather than an Item method:
public class MyCollection {
private NameValueCollection _collection;
[DispId(0)]
public string this[string name] {
get { return _collection[name]; }
set { _collection[name] = value; }
}
}
It can be used from ASP like:
Dim collection
Set collection = Server.CreateObject("MyCollection")
collection("key") = "value"
Response.Write(collection("key")) ' should print "value"
Note: I could not get this to work earlier because I had overloaded the indexer, this[string name] , with this[int index] .
Thanks to Rob Walker's tip, I got it working by adding the following method and attribute to MyCollection:
[DispId(0)]
public string Item(string key) {
return this[key];
}
Edit: See this better solution which uses an indexer.
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