Passing an int array by refеrence to a shell function - how?

[iliyang]

OK, but the function prototype is: protected static extern IntPtr SendMessage(IntPtr hWnd, int msg, int wParam, ref int lParam) that is, I have to pass an integer, not an interger pointer...

[jjansen]

iliyang wrote: that is, I have to pass an integer, not an interger pointer... The syntax is: lResult = SendMessage( // returns LRESULT in lResult (HWND) hWndControl, // handle to destination control (UINT) HDM_GETORDERARRAY, // message ID (WPARAM) wParam, // = (WPARAM) (int) iSize; (LPARAM) lParam // = (LPARAM) (LPINT) lpiArray; ); where lpiArray is: Pointer to an array of integers that receive the index values for items in the header. So you do have to pass an array (even if the array is only one element long). The pointer in the code of my previous post is merely a pointer to the FIRST integer in a row. From there the app can access the next integer, and the next, and so on. It will assume there are iSize integers in a row, starting at the address that is the pointer.

[iliyang]

OK, 10x a lot! It worked finde when I called the function like this: int[] MyArrayOfInts = ... fixed(int* p_MyArrayOfInts = MyArrayOfInts) { ThatFunction(*p_MyArrayOfInts); // not: ThatFunction(p_MyArrayOfInts); }

[jjansen]

Huh? :confused: That's not a pointer to an array you're putting in the function but the value of the first array element. Anyhow, I was going to recommend an alternative method. The Interop-call to SendMessage should look something like this: [DllImport("user32.dll"] public static extern int SendMessage(IntPtr hwnd, uint wMsg, IntPtr wParam, IntPtr lParam); You can get an IntPtr to your array using Marshal.Copy(Int[] source, int startIndex, IntPtr destination, int length). I've never used Marshal.Copy before, so if you're decide to try it this way let me know how it turns out.

[iliyang]

Yes, I know that I'm passing the first element of the array, but I just tried and it worked fine :) The second method (with the IntPtr) I found ealier but I didn't know how to obtain an IntPtr object. I suppose with the IntPtr is better too. But how should I get an IntPtr object to copy the array into?

[jjansen]

Just make one: int[] MyArray = ... IntPtr MyPointer = IntPtr.Zero; // make and initialize Marshal.Copy(MyArray, 0, MyPointer, MyArray.Length); (Note: Don't confuse the marshal-call with the overload Marshal.Copy(IntPtr, int[], int, int) .)

[iliyang]

Nope, Marshal.Copy throws a NullReference exception when passing a null (0) IntPtr object. So for now, the "mystical" solution works the best :rolleyes:

[jjansen]

You're right, my mistake. I wrongly assumed that the Copy method returns a pointer to the array. On second thought this isn't what Copy does at all. Instead you have to allocate some space yourself using Marshal.AllocHGlobal with the appropriate number of bytes. This gives you a valid IntPtr. int Nr = ...; // number of elements in array int[] MyArray = new int[Nr]; IntPtr MyPtr = Marshal.AllocHGlobal(Nr * sizeof(int)) Then call SendMessage with MyPtr. Next use the Copy(IntPtr MyPtr, int[] MyArray, 0, MyArray.Length) method. Finally use Marshal.FreeHAlloc.

[iliyang]

Well, this time works but the values returned are messed. But, you know, this does work fine: _columnOrder = new int[this.Columns.Count]; int size = 0; IntPtr pHeader = SendMessage(this.Handle, (int) Win32.Consts.LVM_GETHEADER, 0, ref size); SendMessage(pHeader, (int) Win32.Consts.HDM_GETORDERARRAY, _columnOrder.Length, ref _columnOrder[0]); See the ref _columnOrder[0] in the second SendMessage call ;)

[jjansen]

OK, good luck with your project.