Have you checked my sample application for lib-gwt-file (it is called
lib-gwt-file-test) ? There is a part which does that. I have a
CSS-hidden FileUploadExt, and a regular GWT button. When the button is
clicked, it invokes the FileUploadExt.click() method, which causes the
browser to display the platform file selection dialog.
You can find it here:
http://www.vectomatic.org/mvn-sites/lib-gwt-file-test-latest/xref/org/vectomatic/file/client/TestAppMain.html#281
(code)
http://www.vectomatic.org/gwt/lib-gwt-file-test-latest/lib-gwt-file-test.html
(online app)
https://github.com/laaglu/lib-gwt-file-test (github repo)
I have another piece of code online which also does that. In my online
SVG editor, I trigger a file selection dialog from an Ext-GWT menu:
https://github.com/laaglu/svgreal
http://www.vectomatic.org/gwt/svgreal-latest/svgreal.html?demo=013
http://www.vectomatic.org/mvn-sites/svgreal-latest/xref/org/vectomatic/svg/edit/client/SvgrealApp.html#673
Regards,
Lukas