Question

I have control (implemented C#, .Net 2.0) that inherits from combobox. It has filtering and other stuff. To keep UI right, when amount of items during filtering falls, drop down list changes its size to fit the number of items left (it is done by NativeMethods.SetWindowPos(…)).

Is there any way to check if drop down list is revealed up or down (literally) – not to check if it is open, it is open, but in which direction, upwards or downwards?

cheers, jbk

Answer 1

So i found an answer:

Here we have both handles to combobox:

    /// <summary>
    /// Gets a handle to the combobox
    /// </summary>
    private IntPtr HwndCombo
    {
        get
        {
            COMBOBOXINFO pcbi = new COMBOBOXINFO();
            pcbi.cbSize = System.Runtime.InteropServices.Marshal.SizeOf(pcbi);
            NativeMethods.GetComboBoxInfo(this.Handle, ref pcbi);
            return pcbi.hwndCombo;
        }
    }

And to dropdownlist of combobox:

    /// <summary>
    /// Gets a handle to the combo's drop-down list
    /// </summary>
    private IntPtr HwndDropDown
    {
        get
        {
            COMBOBOXINFO pcbi = new COMBOBOXINFO();
            pcbi.cbSize = System.Runtime.InteropServices.Marshal.SizeOf(pcbi);
            NativeMethods.GetComboBoxInfo(this.Handle, ref pcbi);
            return pcbi.hwndList;
        }
    }

Now, we can get rectangles from handles:

    RECT comboBoxRectangle;
    NativeMethods.GetWindowRect((IntPtr)this.HwndCombo, out comboBoxRectangle);

and

    // get coordinates of combo's drop down list
    RECT dropDownListRectangle;
    NativeMethods.GetWindowRect((IntPtr)this.HwndDropDown, out dropDownListRectangle);

now we can check:

    if (comboBoxRectangle.Top > dropDownListRectangle.Top)
    {
         ....
    }