Sets the selected file for this file dialog window to be the specified file. This file becomes the default file if it is set before the file dialog window is first shown.
When the dialog is shown, the specified file is selected. The kind of selection depends on the file existence, the dialog type, and the native platform. E.g., the file could be highlighted in the file list, or a file name editbox could be populated with the file name.
This method accepts either a full file path, or a file name with an extension if used together with the setDirectory
method.
Specifying "" as the file is exactly equivalent to specifying null
as the file.