UNITY3D中设置文件选择框的范例：

using OpenWinForm = System.Windows.Forms;
在unity3d中，使用FileDialog应该把System.Windows.Forms.dll拷贝到unity工程的plugins目录，
并且把Player Setting中Other Settings下的api compatibility Level改为.NET2.0。要不无法编译通过。
//比如unity3d要让用户选择某个音乐文件播放;
private void SelectMusic(){
        OpenWinForm.OpenFileDialog op = new OpenWinForm.OpenFileDialog();
        op.Title = "音乐";
        op.Filter = "音频文件(*.wiseglove;*.ogg)|*.wiseglove;*.ogg";
        if (op.ShowDialog() == OpenWinForm.DialogResult.OK || op.ShowDialog() == OpenWinForm.DialogResult.Yes)
        {
            string selectName = op.FileName;
            customBgmPath.text = selectName;

            string path = customBgmPath.text;      
            WWW www = new WWW("file://"+path);
            if(www.audioClip){
                AudioClip clip = www.audioClip;
                AudioPlayCtr.instance.ChangeBgMusic(clip);
            }
        }
        else {
            return;
        }
    }
    //自定义文件保存文件夹;
    private void SaveCutScreenPath()
    {
        OpenWinForm.FolderBrowserDialog fb = new OpenWinForm.FolderBrowserDialog();
        fb.ShowNewFolderButton = true;
        fb.RootFolder = Environment.SpecialFolder.MyDocuments;
        fb.SelectedPath = "C:";
        fb.Description = "请选择截图保存目录";
        fb.RootFolder = Environment.SpecialFolder.MyDocuments;
        if (fb.ShowDialog() == OpenWinForm.DialogResult.OK || fb.ShowDialog() == OpenWinForm.DialogResult.Yes)
        {
            string selectName = fb.SelectedPath;
            customCutScreenPath.text = selectName;
        }
        else {
            return;
        }
    }

//比如unity3d截图后，弹出对话框用户选择保存路径;
public IEnumerator CutScreent() {
        int width = Screen.width;
        int height = Screen.height;
        yield return new WaitForEndOfFrame(); 
        Texture2D tex = new Texture2D(width, height, TextureFormat.RGB24, false);//设置Texture2D
        tex.ReadPixels(new Rect(0, 0, width, height), 0, 0);//获取Pixels           
        tex.Apply();//应用改变
        byte[] bytes = tex.EncodeToPNG();//转换为byte[]
        Destroy(tex);

        OpenWinForm.SaveFileDialog saveFileDialog = new OpenWinForm.SaveFileDialog();
        saveFileDialog.Filter = "图像文件(*.png)|*.png";
        saveFileDialog.FilterIndex = 2;
        saveFileDialog.RestoreDirectory = true;
        if (saveFileDialog.ShowDialog() == OpenWinForm.DialogResult.OK)
        {
            string fName = saveFileDialog.FileName;
            Stream flstr = new FileStream(fName, FileMode.Create);//文件操作
            BinaryWriter sw = new BinaryWriter(flstr, System.Text.Encoding.Unicode);
            sw.Write(bytes);
            sw.Close();
            flstr.Close();
        }
    }

不忙啊， 调用winform还有个坑， 得注册组件才不会出现 oop, could not register... 等等文字

    /* 注册winform对话框*/
    #region winform
    private System.Threading.Thread CloseOops;
    private bool ThreadRunning = true;
    private void OopsWindowsThreadStart()
    {
        CloseOops = new System.Threading.Thread(ClearOopsWindows) { IsBackground = true };
        ThreadRunning = true;
        CloseOops.Start();
    }
    private void ClearOopsWindows()
    {
        while (ThreadRunning)
        {
            FindAndCloseWindow();
        }
    }

    [System.Runtime.InteropServices.DllImport("user32.dll")]
    public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
    [System.Runtime.InteropServices.DllImport("user32.dll")]
    public static extern int SendMessage(IntPtr hWnd, uint Msg, int wParam, int lParam);

    public const int WM_SYSCOMMAND = 0x0112;
    public const int SC_CLOSE = 0xF060;

    public static void FindAndCloseWindow()
    {
        IntPtr lHwnd = FindWindow(null, "Oops");
        if (lHwnd != IntPtr.Zero)
        {
            SendMessage(lHwnd, WM_SYSCOMMAND, SC_CLOSE, 0);
        }
    }
    #endregion

记得在脚本程序的 start()函数里调用下  OopsWindowsThreadStart（）， 到此较好呈现winform对话框。