Is it safe to conclude the basic relationships among GWT panels and widgets below? A GWT panel is translated into a parent DOM node that can contain child panels or/and child widgets. A GWT widget is translated into a leaf DOM node that is merely self-contained. GWT RootPanel must solely act as the root container of all other panels and widgets.

gwt

sof

Reputation: 9649

GWT panels and widgets

Is it safe to conclude the basic relationships among GWT panels and widgets below?

A GWT panel is translated into a parent DOM node that can contain child panels or/and child widgets.
A GWT widget is translated into a leaf DOM node that is merely self-contained.
GWT RootPanel must solely act as the root container of all other panels and widgets.

Upvotes: 1

Answers (2)

kapandron

Reputation: 3671

Here's GWT hierarchy:

GWT hierarchy

A panel is also a widget. Panels are widgets which can contain other widgets and panels. In generally they are used for layout and only rarely have data associated with them directly - the DisclosurePanel for example, can have data in the header, and the TabPanel's tabs. Some are based on an HTML table element(e.g. HorizontalPanel) and some are based on the tag div.

RootPanel is the panel to which contains other widgets. This panel is at the top of the containment hierarchy. The default it wraps tag body of the host-page. RootPanel can contain any number of widgets, which will be laid out in their natural HTML ordering.

See docs.

Upvotes: 2

Colin Alworth

Reputation: 18331

Every GWT Widget instance has an element (reachable by calling getElement()), and panels are just a kind of Widget - they still have a base element. Most Widgets build more content to do their work (for example: CheckBox is a span with both an input and a label), and panels may need more than one element as well.

Widgets are appended to other widgets not just because this is how the DOM needs to be arranged, but also to track attaching and detaching widgets from the DOM. Among other things, this makes it possible to wire up event handlers only when actually attached, and unwire them when no longer part of the page.

RootPanel is a special widget that represents existing elements, either the body itself, or an element with a given ID. There may be more than one RootPanel, but they should not be nested. (That said, there may only be exactly one RootLayoutPanel, a sort of specialized RootPanel that also handles passing browser size information to child layout panels).

This may be the same idea that you were after, but I wanted to clarify that a Widget is frequently more than a single DOM node.

Upvotes: 2

GWT panels and widgets

Answers (2)

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