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The Diagram View

The diagram view contains two important elements, rounded rectangles, which represent nodes, and lines. Class diagrams may also contain annotations (described in “Class Modeling With Xcode Design Tools”).

In this section:

Diagram Elements
Diagram Tools
Roll-Up and Expansion
Layout
Multiple Selection
Colors and Fonts

Diagram Elements

The diagram view contains two important elements, “roundtangles” and lines. Class diagrams may also contain annotations (described in the “Class Modeling With Xcode Design Tools”).

Nodes

Nodes are the base elements in the model. In the class model, they are classes, categories, and protocols (interfaces in Java); in the data model they are entities.

A node may be split into three sections: The title bar containing the name of the element (including the namespace or package for C++/Java), and two compartments. The compartments show attributes and relationships in data models and properties (instance variables) and operations (methods or member functions) in class models (see Figure 10-3).

Lines

The semantic meaning of a line is different in the class and data models, and it further depends on whether the line is solid or dashed, what sort of arrowhead is present, and what objects it connects. In class diagrams, you can only edit lines to or from annotations—they are created automatically based on the inheritance hierarchies defined by the code in your project.

Diagram Tools

The diagram view provides several tools, whose function should be familiar from other drawing packages. You select the tools from the palette in the bottom-left corner of the diagram view, shown in Figure 10-2.

Arrow

You use the arrow tool to make selections and to move and resize graphic elements.

Text (Class Diagrams Only)

You use the text tool to annotate diagrams in a class model. To edit text in the text area, simply double click inside the element. You can use the Formatting menu, Font panel, Colors panel and so on to format the text as you wish. You can use the line tool to connect a text area to a specific class.

Line

You use the line tool to add a relationship in data model or to connect a comment to a specific class in a class model. To connect two elements, select the line tool, then drag from one end of the connection to the element at the other end. Note that in a data model, when you are establishing a relationship, you must make the connection from the source to the destination of the relationship.

Magnifying Glass

You use the magnifying tool to zoom into part of the diagram, or, by holding down the Option key, to zoom out . See “Zoom” for other ways to zoom. To effect the zoom, you select the tool, then click inside the diagram.

Hand

You use the hand tool to move the diagram if its bounds extend beyond the current view.

Roll-Up and Expansion

You can display a node and the compartments within it in a variety of ways:

• Rolled up, so that just the name of the class or entity is showing. This gives the most compact representation, with maximum information density in the diagram. (In Figure 10-3 the NSDocument node is rolled up.)

• Compartment titles showing. The titles are Attributes and Relationships in the data model, Properties and Operations in the class model. This gives a compact representation, but with easy access to detail .

• Compartments expanded. All the information in a compartment is visible but at the cost of screen real estate. (In Figure 10-3 the properties compartment of MyDocument is expanded, but the opertations compartment is not.)

To roll up or roll down the node, use Design > Roll Up Compartments or Design > Roll Down Compartments respectively. To hide or expose compartment information, you use the disclosure triangle within a compartment, or Design > Expand Compartments or Design > Collapse Compartments .

Layout

There are a number of options for moving and resizing elements; you can also constrain the way the elements can be moved and resized, and even prevent them from being moved and resized at all. Furthermore, you can zoom into and out of the diagram, and arrange the page layout as you wish.

Moving and Resizing Shapes

You can rearrange elements in a diagram to suit your needs—lines that join elements are updated appropriately. Use the arrow tool to select an element, and then simply drag it. You can move all the elements in the current selection (see “Multiple Selection”) in the same way.

When you select a shape, “handles” appear around its edges (as shown in Figure 10-4). You can drag the handles to resize the shape as you wish.

You can also automatically resize elements in several ways, using the Design > Diagram > Size menu: Make Same Width and Make Same Height resize the selected elements appropriately; Size to Fit resizes the selected elements so that they fully enclose their contents with minimal padding.

Alignment and Grid

You can use a variety of options to automatically align selected elements and to help you keep elements aligned . You can use the menu items in the Design > Diagram > Alignment menu to perform a number of operations, aligning specified edges or centers of a selection and aligning a selection in a row or column.

You can also use a grid to help keep elements aligned. By default, the diagram view displays a background grid, and move and resize operations are snapped to it. Using the Design > Diagram menu, you can turn the grid display on and off; you can also independently turn the snap-to-grid feature on and off.

Automatic Layout

The class modeler provides two ways to automatically lay out elements in a diagram, force-directed layout and hierarchical layout. You access them using the Design > Automatic Layout menu.

With hierarchical layout , parent elements are typically at the top of the diagram, children at the bottom. This gives a generally horizontal layout, and is generally better for deep hierarchies.

The force-directed layout tends to produce circular arrangements, with commonly referenced classes in the middle. This is usually better for shallow hierarchies. Note that the force-directed layout can take unbounded time to calculate—it is not recommended for very large collections.

You can apply the automatic layout feature just to selected items or to the whole diagram. The layout respects the current size of elements in the selection. If you expand or contract a node, then perform automatic layout again, the result is different from what it was prior to the change in size .

Locking

You can lock individual graphic elements in place using Design > Diagram > Lock, or the Lock contextual menu. If you subsequently apply automatic layout, locked elements are unaffected. To unlock an item, use Design > Diagram > Unlock, or the Unlock contextual menu.

Zoom

You can zoom into and out of the diagram in three different ways:

• Use the Design > Diagram menu to zoom in, out, and to fit.

• Use the pop-up menu to select a percentage zoom.

• Use the magnifying glass tool (click to zoom in, Option-click to zoom out).

Page Layout

If you move diagram elements outside the current diagram bounds (whether directly, or through applying automatic layout, or by unhiding elements), the page area automatically expands. Conversely, if you remove elements such that a page is left blank, the page area automatically contracts.

You can adjust the size of a page using the File > Page Setup menu. The page layout adjusts automatically to accommodate a change in page size.

Multiple Selection

You can use multiple selection in the diagram view to move a collection of elements in a flotilla drag, or for roll-up, expand all, and so on. You can make multiple selection in several ways:

• You can select a single element, then hold down the Shift key and click additional elements. Unselected elements are added to the current selection; selected elements are removed from the current selection.

• You can drag the background of the diagram to create a selection rectangle. Elements whose boundaries intersect with this rectangle are selected.

• You can select classes or entities in the browser—the browser selection and diagram selection are kept synchronized.

You can use Edit > Select All to select all elements in the diagram. Note that for items in the Diagram menu, clicking on the background (rather than a drawn element) is the equivalent of selecting all, but may be faster.

Colors and Fonts

The diagram view provides default coloring for various elements . By default, all text is black, and the title bar and outline of drawing elements are colored. In the data model the color is the same for all entities.

You change the background color of the title bar and color of the outline of elements by dropping a color swatch from the Color panel onto the element. You change the other color settings, and the font used for the title, property, and operations text, using the Appearance pane of the Info window (inspector). You can also select multiple elements and change their color and text settings simultaneously, as shown in Figure 10-5.

You can also change the default settings for the entire model using the Appearance pane—see “Info Window.”

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