如何在没有图标的情况下显示文档窗口的标题？

Now I drag a file to the app icon in the dock, this app is based on document . I found that no little image on the left of window title after the app is run and the mainwindow is open . but when I drag a file to the dock icon before the app run and use this method to run the app , a little image on the left of window title to show the file ,just like the xcode etc. Now I want to show the little image both way or not to show the little image both way , How to do ? I think that it maybe the window property based on document , but I don't know how to fix it ? Thanks!Now I drag a file to the app icon in the dock,