/// <summary>
/// Retrieves a DsObject structure from the "array" in our DsObjectNames structure.
/// Because marshalling cannot properly marshal a nested, variable sized
/// array in a struct, we have to do this the hard way.
/// That is, the "array" of DsObjects that's in our managed DsObjectNames structure
/// definition is merely a pointer to a big chunk of data that we have to manually
/// retrieve DsObjects from by manipulating pointers, rather than doing aObjects[i].
/// </summary>
/// <param name="index">The index of the DsObject to retrieve</param>
/// <returns></returns>
private UnsafeNativeMethods.DsObject GetDsObjectForIndex(int index)
{
ThrowIfDisposed();
//Ensure we're within proper bounds.
if (index < 0 || index >= Count)
{
throw new ArgumentOutOfRangeException("index");
}
//Now we calculate the offset of the specified array index.
//This is the address of the first element in the array, plus
//the number of entries past that times the size of an entry, or:
//offset = StartOfStructAddress + FirstArrayEntryOffset + index * SizeOfEntry
IntPtr offset = new IntPtr(_ptrToDsObjectNames.ToInt64() +
_dsObjectArrayFieldOffset +
index * _sizeOfDsObject);
//Marshal that to a DsObject structure.
UnsafeNativeMethods.DsObject dsObject =
(UnsafeNativeMethods.DsObject)Marshal.PtrToStructure(offset,
typeof(UnsafeNativeMethods.DsObject));
return dsObject;
}
/// <summary>
/// Extracts the name for the specified entry number from the DsObjectNames data
/// </summary>
/// <param name="index">The index of the name to retrieve</param>
/// <returns></returns>
private String BuildStringForItemName(int index)
{
ThrowIfDisposed();
//Ensure we're within proper bounds.
if (index < 0 || index >= Count)
{
throw new ArgumentOutOfRangeException("index");
}
//First we have to get a DsObject out of the array (aObjects) of DsObjects.
//The information in this struct will tell us where to find the name data
//we want.
UnsafeNativeMethods.DsObject dsObject = GetDsObjectForIndex(index);
//The offset of the name from the start of the DsObjectNames structure is stored in
//the corresponding DsObject's offsetName field, so the pointer to the beginning of the
//string can be computed as:
//
// offset = StartOfStructAddress + dsObject.offsetName;
IntPtr nameOffset = new IntPtr(_ptrToDsObjectNames.ToInt64() + dsObject.offsetName);
//We marshal this pointer to a string and return it.
return Marshal.PtrToStringAuto(nameOffset);
}
