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Articles Reviews Oracle
Written by Bogdan V   
Tuesday, 31 October 2006
Article Index
Using Oracle Forms  Hot
Single-Record and MultiRecord Blocks
Canvases
Page 3 of 3



Canvases are the Form components that are used to display items on the screen. By arranging items on one or more canvases, they can be presented logically to the user.

There are several types of canvases that can be displayed within the windows of the Form.

These include Content, Stacked, Tabbed, and Toolbar canvases.

Content Canvas

A Content canvas is the “background” of the window. It is a type of canvas that completely fills the window that it is in. If the canvas is larger than the window, it is cropped; if the canvas is smaller than the window, Forms will fill in the extra space with the specified background color. Since a content canvas completely fills the window, only one content canvas can be seen at any time. If the form navigates to an item on a different canvas, then that new content canvas replaces the currently displayed canvas.

If the canvas is larger than the window/view in which it is displayed, scrollbars can be added to the window to display all the items. Good design principles, however, suggest that you do not scroll more than two window-widths in any direction, and do not allow scrolling both horizontally and vertically in one form.

Stacked Canvas

A stacked canvas can be layered on top of a content canvas, and is used to hide part of the content canvas or display alternate data. For example, a form designed to display customer information may display the common customer information at the top of the canvas and allow either financial data, order data, or contact information to be displayed on the bottom half of the window.

Each set of data is arranged on a stacked canvas that is displayed in the same position. When the user wants to see order data, the stacked canvas with order data is “brought to the top.”

In most cases, the size of a stacked canvas is smaller than the window it is displayed in, because the stacked canvases are used to cover up only part of the content canvas in the window. If it is not smaller than the existing canvas, then the stacked canvas will completely obscure the content canvas, which defeats the purpose of having an alternate view.


Stacked canvases can be displayed and hidden programmatically. They are also displayed automatically when the user navigates to an item on the canvas. A stacked canvas will remain in view until it is explicitly dismissed or replaced by another canvas.

A common error that can occur is that stacked canvases can disappear at inopportune times. This is usually related to the automatic re-ordering that Forms uses to display the active item. In this case, something that has to be displayed in order to show the active item has overlapped the stacked canvas and caused it to be pushed farther down in the stack of displayed canvases.

Tabbed Canvas

Tabbed canvases are a specialized type of stacked canvas that has multiple pages of information identified by folder-like tabs across the top or side of the display. Each tab page can contain different data, which is easily accessed by clicking the identifying tab.

Tabbed canvases are two-part objects: the Tab Canvas itself is the container, which contains multiple Tab Pages. Remember that Forms insists that the “active item” is displayed at all times. This can cause confusion when working with Tabbed canvasses. Because Forms considers the Tab Canvas itself as the display canvas, not the individual pages, it is possible to have a Tab Page displayed that does not contain the current item. As long as the Tab Canvas is displayed, Forms is satisfied.

Toolbar Canvas

Finally, Forms has a special type of canvas for custom button bars. Forms has a default “smartbar” toolbar that is included in each Form to provide the standard functionality for cut and paste, save, etc., and can be seen in Figure 3-3. If you need a custom toolbar, this type of canvas can be used as a replacement.
 

Forms has a special type of canvas for custom button bars. Forms has a default “smartbar” toolbar that is included in each Form to provide the standard functionality for cut and paste, save, etc

   Figure 3-3:  Displaying a simple form in a web browser.

When a form is displayed in the browser window, the “active” item—that is, the item with focus—must be displayed. Using the order of blocks and items, Forms determines which item should be the “starting” place in the form. Forms will do whatever is necessary to display that item within the open view port on screen. If the item is not in the current view, then the Form will manipulate the layers of display to ensure that the item can be seen. When the user (or internal code) navigates to another item, that item will then be brought into the view port if it is not already visible.

 

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1 of 4 people found the following review helpful

thanks, Thursday, 26 February 2009

Written by silvia

Overall rating
5.0
Thank you.
It helps me a lot for doing my paper. :)
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2 of 3 people found the following review helpful

Bogdan V
thanks, Sunday, 14 September 2008

Written by Bogdan V   -  View all my reviews  - #1 Reviewer

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5.0
what can i say, just thank you and i will try my best to add more articles.
regards bogdan,
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4 of 5 people found the following review helpful

A very good overview, Thursday, 24 July 2008

Written by aishwarya

Overall rating
5.0
the overview on forms given here is wonderful specially for starters like me. The explanation given about forms is really crip and clear..Kindly request you to add more lessons...
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