ErrorPanel
A titled block that shows the messages an error fence caught. It is the component DomUI puts on a page that has nothing else to show them with.
Div panel = new Div();
cp.add(panel);
panel.setErrorFence(); // Messages from below stop here...
panel.add(new ErrorPanel()); // ...and this shows what was caught
What it does
An ErrorPanel needs nothing but to be added: on the way into the page it looks
for the nearest error fence above it and registers itself as a listener of that
fence, and when it is removed it deregisters again. Everything after that is
automatic - it has no methods of its own worth calling.
- It is invisible while there is nothing to show, and appears the moment the first message arrives.
- Its title follows the severest message in it: "Errors on the page", "Warning(s) on the page" or the info header.
- Each message is written with its error location in bold in front of it, and the
control a message belongs to gets the
ui-input-errclass - which is what makes the field turn red.
Where it comes from by itself
A page usually never makes one. When a message arrives at a fence that has no listener at all, the framework asks the application for a display component:
@Override public void addDefaultErrorComponent(NodeContainer page) {
ErrorPanel panel = new ErrorPanel();
page.add(0, panel);
}
That is DomApplication.addDefaultErrorComponent(), and it is the reason a page
that does nothing about errors still shows them. Overriding that one method
changes how messages appear in the whole application - which is where an
application decides between this component and
ErrorMessageDiv, and where in the page they land.
Which of the two to use
ErrorPanel is a block with a caption around the messages: it is meant to be
noticed, and it fits at the top of a page or a dialog. ErrorMessageDiv writes
the bare lines with no title and no frame, which is what fits inside a panel, a
tab or a fragment that only has room for one line.