About Stacked Canvases
Stacked canvases are displayed in a window along with the window's content canvas(es) and any number of other stacked canvases. You can set the bevel, color, and pattern attributes of a stacked canvas to make it look different than the underlying content canvas. Contrarily, you can make the stacked canvas look like the content canvas, and then show and hide the stacked canvas programmatically so end users are unaware that a separate canvas is being displayed.
This technique can be used to make items or boilerplate appear to change dynamically. When navigating from a content canvas item to a stacked canvas item, you can only see the stacked canvas, since the content canvas disappears.
Creating a stacked canvas is similar to creating a content canvas. To define a stacked canvas, you need to set certain canvas properties that apply only to stacked canvases, and create items and boilerplate text and graphics as you would for a content canvas.
Note: To convert an existing content canvas to a stacked canvas, simply change its Canvas Type property from Content to Stacked.
At runtime, stacked canvases are displayed automatically in response to navigation in the same manner as content canvases. To show and hide stacked canvases programmatically, use the SHOW_VIEW, HIDE_VIEW, and SET_VIEW_PROPERTY Built-ins.
Uses for Stacked Canvases
You can use stacked canvases to do the following:
- Display items or boilerplate graphics that end users need to see only in
certain situations. (Define a stacked canvas that displays help text or images
that remain hidden until they are explicitly invoked by the end user.)
- Display headers that display constant information such as company names,
Dates, and status information. (Define a stacked canvas that always appears
in front of the current content canvas. When the current content canvas is
replaced by another, the stacked canvas remains visible in the window. Use
this technique to avoid duplicating interface elements on multiple content
canvases in the same window.)
- Create a block with items that scroll dynamically in the window where they
are displayed, much like a spreadsheet. (If a block contains more items than
fit in a window, Oracle Forms automatically scrolls the window as the end
user tabs to items outside the window's frame. This can cause important fields—such
as primary key values—to be scrolled out of the window and thus out of the
end user's view. For example, for a block that displays information about
orders, the Order ID always should be visible, regardless of navigation by
the end user. By placing the Order ID item on the underlying content canvas,
and placing items that can be scrolled out of sight on a stacked canvas, the
stacked canvas becomes the scrolling region, rather than the window itself.
Note that stacked canvases can have their own scroll bars, independent of
the window's scroll bars.)
Related topics
Creating a stacked canvas
Editing a stacked canvas in the Layout Editor
Working with the Raise on Entry canvas property
About stacking order
Manipulating a stacked canvas programmatically