how to use GetSaveFileName API in c#

See more:

.NET2.0

C#

.NET

WinForms

I don't want to use SaveFileDialog class to pop dialog.
because some reasons,i want to use the api GetSaveFileName,but some parameters within c# i don't know how to define ,can anybody give demo and show me how to use this API.
My question's important is about parameter but not use dllimport.
thanks for you answer.

my demo is below，but it can't pop dialog:

public partial class Form1 : Form
{
    public struct OPENFILENAMEA
    {
        public uint lStructSize;
        public uint hwndOwner;
        public uint hInstance;
        public uint lpstrFilter;
        public uint lpstrCustomFilter;
        public uint nMaxCustFilter;
        public uint nFilterIndex;
        public uint lpstrFile;
        public uint nMaxFile;
        public uint lpstrFileTitle;
        public uint nMaxFileTitle;
        public uint lpstrInitialDir;
        public uint lpstrTitle;
        public uint Flags;
        public ushort nFileOffset;
        public ushort nFileExtension;
        public uint lpstrDefExt;
        public uint lCustData;
        public uint lpfnHook;
        public uint lpTemplateName;
    }

    [DllImport("comdlg32.dll", CharSet = CharSet.Auto, SetLastError = true)]
    public static extern bool GetSaveFileName(OPENFILENAMEA ofn);

    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        OPENFILENAMEA ofn = new OPENFILENAMEA();
        bool isTrue = GetSaveFileName(ofn);

    }
}