SplitLayoutPanel.setSize

[peter tong]

I have a RootPanel and a SplitLayoutPanel, I found when I add the SplitLayoutPanel inside RootPanel, the SplitLayoutPanel size is not auto fill all space of RootPanel,
but need call setSize and there is no corresponding RootPanel.getSize(), so I need try and error to set the parameter of SplitLayoutPanel.setsize to make it fill all the space of RootPanel.
is this a must to call setSize to make the ineer SplitLayoutPanel fill all the space of RootPanel?

RootPanel rootPanel = RootPanel.get();
SplitLayoutPanel splitLayoutPanel = new SplitLayoutPanel();
splitLayoutPanel.setSize("xx", "xx");  // try and error to find the expect width and height value, no wiser method?
rootPanel.add(splitLayoutPanel, 0, 0);