Scope of document

• Component Developers
• Clients of XPCOM (for information only)

Why Component Loaders

Component Loaders

Internally XPCOM maps the passed in CONTRACTID to a CID and then the CID maps into a DLL name. XPCOM loads the DLL assuming the dynamic loading mechanism to create a factory. Then, asks the factory to create a particular instance. Here are roughly the steps involved:

1. CreateInstance(..., CONTRACTID,...)
2. Map CONTRACTID to CID
3. Map CID to DLL
4. factory = Dynamically Load DLL to create Factory
5. Use Factory to create object instance

• CreateInstance(..., CONTRACTID,...)
• Map CONTRACTID to CID
• Map CID to ComponentType
• If ComponentType is DLL
• factory = Dynamically Load DLL to create Factory
• else
• ComponentLoaderServiceCONTRACTID = "@mozilla.org/xpcom/component-loader;1?type=" + ComponentType ^*
• loaderInstance = GetService(..., ComponentLoaderServiceCONTRACTID,...)
• factory = loaderInstance->CreateFactory(..., componentLocation,...)
• Use Factory to create object instance

Format of ComponentType

ComponentType is assumed to be mimetype.

Component Registration

Registration of components in DLLs wont change. ComponentType of DLL is assumed here. To facilitate registration of components with specifc component types, the component manager will provide the following API:

RegisterComponentWithType(const nsCID &aClass,
                          const char *aClassName,
                          const char *aContractID,
                          const char *aComponentType,
                          const char *aComponentLocation,
                          PRBool aReplace,
                          PRBool aPersist);
 
 

Component Loader Service Registration

Since the loader is just another component with a special contractid, there is no special registration of the component loader.  Component Loaders use either the RegisterComponent() api if they are a DLL (most common) or use RegisterComponentWithType() api if they are themselves of a particular type (very rare).

Autoregistration of non DLL Components and Component Loaders

^* ContractID syntax might change