MS Word Automation in C# - Unable to cast object of type 'System.String[*]' to type 'System.String[]'

Question

I use this code to get a String array of headings used in a MS Word 2007 document (.docx):

dynamic arr = Document.GetCrossReferenceItems(WdReferenceType.wdRefTypeHeading);

Using the debugger, I see that arr is dynamically assigned a String array with titles of all my headings in the document (about 40 entries). So far so good.

Then, I want to access the strings, but no matter how I do it, I get the following exception:

InvalidCastException: 
           Unable to cast object of type 'System.String[*]' to type 'System.String[]'.

I have tried different ways of accessing the strings:

By index:

String arr_elem = arr[1];

By casting to an IEnumerable:

IEnumerable list = (IEnumerable)arr;

By using a simple foreach loop:

foreach (String str in arr)
{
   Console.WriteLine(str);
}

However, no matter what I try, I always end up with the same exception as shown above.

Can anyone explain what I am missing here / what I am doing wrong? And especially String[*] - what does it mean?

Answer 1

string[] is a vector - a 1-d, 0-based array. string[*], however, is a regular array that just happens to have one dimension. Basically, you are going to have to handle it as Array, and either copy the data out, or use the Array API rather than the string[] API.

This is the same as the difference between typeof(string).MakeArrayType() (the vector) and typeof(string).MakeArrayType(1) (a 1-d non-vector).

Answer 2

try

object arr_r = Document.GetCrossReferenceItems(WdReferenceType.wdRefTypeHeading);
Array arr = ((Array) (arr_r));

string myHeading = (string) arr.GetValue(1);

Answer 3

The problem is that you're using dynamic in a situation where it apparently wasn't intended. When the dynamic runtime sees a 1D array, it assumes a vector, and tries to index into it or enumerate it as if it were a vector. This is one of those rare cases where you have a 1D array that is not a vector, so you have to handle it as an Array:

Array arr = (Array)(object)Document.
            GetCrossReferenceItems(WdReferenceType.wdRefTypeHeading);
// works
String arr_elem = arr.GetValue(1);
// now works
IEnumerable list = (IEnumerable)arr; 
// now works
foreach (String str in arr)
{
    Console.WriteLine(str);
}