Registering VB Objects with the ROT in Java

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Registering VB Objects with the ROT
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Registering a Multiuse VB object in the ROT is easy First, determine the CLSID At runtime the CLSID can be found with the CLSIDFromProgID API function or stored as a string constant if you're sure it's not going to change You can turn the string into a CLSID using the CLSIDFromString function defined in VBoostTypes The CLSID is static if binary compatibility is enabled You can also determine the CLSID at runtime by using the CLSIDFromFileAndClassName function in the LookupCLSIDBas file on the book's CD With the CLSID in hand you may think that you are now ready to finish registering your object in the ROT with a simple call to RegisterActiveObject However, life becomes difficult when you do that RegisterActiveObject adds one or more references to the object, so the act of adding the object to the ROT keeps
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the object from being in the ROT and hitting its Class_Terminate event at the same time If you intend to terminate an ActiveX server gracefully, it is completely unacceptable to have outstanding references on an object You are stuck in the ROT until someone happens to explicitly remove you Even if the process ends (without running the termination code), the entry you placed in the ROT remains there until you reboot the machine The ROT has no way to clean up after itself To be a good COM citizen, you must be able to put the object in the ROT and run termination code when the only thing keeping the object alive is the references held by the ROT You can't do this with a normal VB object However, a highly specialized lightweight object, called ROTHook, allows the object to be in the ROT and terminate correctly I'll first look at how to use the ROTHook object and then delve into its implementation
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Using the ROTHook Object The ROTHook object is very easy to use in spite of its complexity under the covers The ROTHook structure has two members: Hook and Struct Hook points to the lightweight object implementation in Struct and has type IROTHook The IROTHook interface has two methods, ExposeObject and HideObject, and one property, Locked ExposeObject's first parameter is the object to place in the ROT, usually Me The second parameter is the object's ProgID The following steps are sufficient to place the first object in the ROT and to get it out again 1 Create an ActiveX EXE project 2 Establish a global VBoost variable by adding VBoostBas and the appropriate project references (see "VBoost Objects" in 1 or Appendix A) 3 Add a project reference to VBoost: ROT Hook Types You'll find this library in ROTHookTypesOlb 4 Add the ROTHookBas file to your project 5 Add the following code to a class with the Instancing property set to MultiUse or GlobalMultiUse class
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'Class DemoClass Private m_ROTHook As ROTHook Private Sub Class_Initialize() InitROTHook m_ROTHook m_ROTHookHookExposeObject Me, "ROTDemoDemoClass" End Sub Private Sub Class_Terminate() m_ROTHookHookHideObject End Sub Creating a DemoClass instance from inside or outside the project now places the object in the ROT, and GetObject(, "ROTDemoDemoClass") successfully retrieves the registered instance of the class The object stays in the ROT until the last object retrieved via an external CreateObject or GetObject is released or until you make an explicit call to HideObject If you never create an object from within the same project, such as when you have a server that has no UI, the object is always created and released externally The HideObject call in Class_Terminate is not needed to remove the ROT entry in the no-UI case Debugging with ROTHook You have to be aware of ROT implications when you debug projects that include registered objects from inside the IDE The ROTHook object works well in the IDE, except for the debugging limitations that result from an IUnknown hook (see "IUnknown hooking" in 5) If you stop the program with the End statement or the End button, you don't run normal termination code, and you can leave garbage in the ROT The system can generally work around the orphaned entries, but it does not clean them up until you reboot To help you end a debugging session cleanly, ROTHookBas includes a debug function, ClearROT, that you can call from the immediate pane by calling HideObject on all the currently registered objects To enable this capability, you must add the conditional compilation constant DEBUGROT and set it to a nonzero value You should turn the debugging code off before making an executable There are a couple of tools that can help you debug the ROT The first tool, IROTViewExe, ships in the Tools\OLETools directory on the VB CD IROTView lets you look at the names of all objects currently in the ROT You can see this list
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