PRB: Script Error Occurs When Referencing Non-variant Array

• Microsoft Visual Basic, Scripting Edition, versions 1.1, 2.0, 3.0
• Microsoft JScript, versions 1.0, 2.0
• Microsoft Internet Explorer (Programming) version 4.0
• Active Server Pages

SYMPTOMS

When a script attempts to reference the elements of an array returned by a component, the script engine reports:

"Object doesn't support this property or method '<object>.<method>'"

CAUSE

The VBSCRIPT active scripting engine supplied by Microsoft only supports the indexing of SAFEARRAYs of VARIANTs. While VBSCRIPT is capable of accepting arrays of non-variant type for the purposes of boundary checking and passing it to other automation objects, the engine does not allow manipulation of the array contents at this time.

The JSCRIPT active scripting engine does not provide support for testing the bounds or indexing SAFEARRAYs of any type including VARIANTs. However, JSCRIPT is capable of passing SAFEARRAYs from one automation object to another.

RESOLUTION

To function correctly with applications and components that host VBSCRIPT, automation objects should create SAFEARRAYs of VARIANTs. Non-VARIANT data should be packaged in the VARIANT elements of the SAFEARRAY to be returned to the VBSCRIPT engine.

Scripts written in VBSCRIPT should use the TypeName function to check the data type of a variable. The TypeName function returns the string "Variant()," excluding the quotes, when passed an array of VARIANTs.

Scripts written in JSCRIPT should use the typeof operator to test the data type of a variable. The typeof operator returns the string "unknown," excluding the quotes for datatypes unsupported by JSCRIPT.

STATUS

This behavior is by design.

MORE INFORMATION

The VBSARRAY is a simple Active Template Library (ATL) version 2.1 component object that demonstrates this behavior. The component implements a dual interface Ivbsa that supports three methods: TestBstrs, TestVariants, and TestPassArray. The first demonstrates the problem by returning a SAFEARRAY of BSTRs. The second demonstrates the solution by packaging each of the BSTRs in a VARIANT. The third demonstrates that an array of non-VARIANT type can be passed from component to VBSCRIPT or JSCRIPT to component. The data remains intact.

Here is the implementation of TestVariants:

      // Return a VARIANT array of VARIANTs which hold BSTRs
      STDMETHODIMP Cvbsa::TestVariants(VARIANT * pvaVariant)
      {
         HRESULT hr = NOERROR;
         LPSAFEARRAY psa;
         SAFEARRAYBOUND rgsabound[]  = { 3, 0 }; // 3 elements, 0-based
         int i;

         if (!pvaVariant)
         {
            return E_INVALIDARG;
         }

         VariantInit(pvaVariant);

         psa = SafeArrayCreate(VT_VARIANT, 1, rgsabound);
         if (!psa)
         {
            return E_OUTOFMEMORY;
         }

         VARIANT vFlavors[3];
         for (i = 0; i < 3; i++)
         {
            VariantInit(&vFlavors[i]);
            V_VT(&vFlavors[i]) = VT_BSTR;
         }

         V_BSTR(&vFlavors[0]) = SysAllocString(OLESTR("Vanilla"));
         V_BSTR(&vFlavors[1]) = SysAllocString(OLESTR("Chocolate"));
         V_BSTR(&vFlavors[2]) = SysAllocString(OLESTR("Espresso Chip"));
         if (!V_BSTR(&vFlavors[0]) || !V_BSTR(&vFlavors[1]) ||
             !V_BSTR(&vFlavors[2]))
         {
            hr = E_OUTOFMEMORY;
            goto Error;
         }

         {
                //Plug references to the data into the SAFEARRAY
               LPVARIANT rgElems;
               if (FAILED(hr = SafeArrayAccessData(psa,(LPVOID*)&rgElems)))

            {
               goto Error;
            }
            for (i = 0; i < 3; i++)
            {
               rgElems[i] = vFlavors[i];
            }
            SafeArrayUnaccessData(psa);
         }

         V_VT(pvaVariant) = VT_ARRAY | VT_VARIANT;
         V_ARRAY(pvaVariant) = psa;

         return NOERROR;

   Error:
         for (i = 0; i < 3; i++)
         {
            if (V_BSTR(&vFlavors[i])
            {
               VariantClear(&vFlavors[i]);
            }
         }
         return hr;
   } 

      <SCRIPT LANGUAGE=JSCRIPT>
      function JScriptSafeArrayTest()
      {
         pvaBstr = SimpleComponent.TestBstrs()
         if (typeof(pvaBstr) == "unknown")
         {
            Alert("JSCRIPT cannot handle the type returned by TestBstrs()")
            SimpleComponent.TestPassedArray(pvaBstr)
         }

         pvaVariant = SimpleComponent.TestVariants()
         if (typeof(pvaVariant) == "unknown")
         {
         Alert("JSCRIPT cannot handle the type returned by TestVariants()")
            SimpleComponent.TestPassedArray(pvaVariant)
         }
      }
      </SCRIPT> 

1. Follow the instructions below on obtaining the sample component VBSARRAY.DLL and sample page VBSARRAY.HTM.



2. Register the component VBSARRAY.DLL using a tool such as REGSVR32.EXE.



3. Launch Internet Explorer, and load the test page VBSARRAY.HTM.



4. Follow the instructions on the page, clicking the various buttons and observing the resulting behavior.

Vbsarray.exe

http://www.microsoft.com/downloads/search.asp

REFERENCES

Platform SDK Automation Reference

Microsoft Visual Basic Scripting Edition Language Reference

Additional query words:

Keywords : kbfile kbsample AXSDKScripting
Version : WINDOWS:1.0,1.1,2.0,3.0,4.0; winnt:
Platform : WINDOWS winnt
Issue type : kbprb