Various Canvas Types in Oracle Form

Various Canvas Types in Oracle Form

What is a Canvas?

A canvas is a surface inside a window container on which you place visual objects such as interface items and graphics. It is similar to the canvas upon which a picture is painted. To see a canvas and its contents at run time, you must display it in a window. A canvas always displays in the window to which it is assigned.

Canvas Types

Oracle Forms provides four types of canvases, all of which can be displayed in the same window at runtime. A canvas’ type defines how Oracle Forms will display it in the window to which it is assigned. When you create a canvas, you specify its type by setting the Canvas Type property.

The four canvas types are:

  • Content
  • Stacked
  • Tab
  • Toolbar

Content Canvas:

The most common canvas type is the content canvas (the default type). A content canvas is the “base” view that occupies the entire content pane of the window in which it is displayed. You must define at least one content canvas for each window you create.

When building an application, one of the first steps is to create content canvases that will be displayed in the windows of your form(s). While you can assign more than one content canvas to the same window at design time, at runtime only one content canvas is displayed at one time in the window.

Stacked Canvas:

A stacked canvas is displayed at top—or stacked on—the content canvas assigned to the current window. Stacked canvases obscure some part of the underlying content canvas, and often are shown and hidden programmatically. You can display more than one stacked canvas in a window at the same time.

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.

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. To convert an existing content canvas to a stacked canvas, simply change its Canvas Type property from Content to Stacked.

Tab Canvas:

A tab canvas—made up of one or more tab pages—allows you to group and display a large amount of related information on a single dynamic Oracle Forms canvas object. Like stacked canvases, tab canvases are displayed on top of a content canvas, partly obscuring it. Tab pages (that collectively comprise the tab canvas) each display a subset of the information displayed on the entire tab canvas.

A tab canvas can have many tab pages, and must have at least one. Think of tab pages as the folders in a filing system. Each individual tab page (folder) has a labelled tab that developers and end users click to access the page. At design time or runtime, you click the labelled tab to display the page at the front of the tab canvas, thereby obscuring any other page(s).

Tab pages are sub-objects of a tab canvas. Like the canvas to which it is attached, each tab page has properties; similarly, any item you place on a tab canvas has a canvas property as well as tab page properties. The ordering of tab pages in the Object Navigator determines the left-to-right (or top-to-bottom) order of the tabs at runtime.

Toolbar Canvas:

A toolbar canvas often is used to create toolbars for individual windows. You can create two types of toolbar canvases: horizontal or vertical. Horizontal toolbar canvases are displayed at the top of a window, just under its menu bar, while vertical toolbars are displayed along the far left edge of a window.

You can create toolbar canvases, both horizontal and vertical, for any window in a form. Oracle Forms displays horizontal toolbar canvases across the top of a window, and vertical toolbar canvases on the left edge of a window.

When you create a toolbar canvas, you assign it to a window by setting the canvas Window property, and then register it with the window by setting the window’s Vertical Toolbar Canvas or Horizontal Toolbar Canvas properties as appropriate. You can change the appearance of a toolbar at runtime by dynamically showing and hiding different items on the toolbar. You also can create more than one toolbar for the same window, and display them in response to navigation events and programmatic control, much like stacked canvases assigned to the same window.


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