Volume Number: 19 (2003)
Issue Number: 10
Column Tag: Programming

Mac OS X Programming Secrets

Interface Builder Tips and Tricks

by Scott Knaster

When you're programming with Cocoa, you spend plenty of time in Interface Builder, instantiating objects, positioning things just right in windows, and making connections. In this month's column, we're going to shine the light of day on a few valuable tips and shortcuts for making yourself more productive when using Interface Builder.

Most of the intricate work in Interface Builder is in the design window, which is where you add objects from palettes, lay them out, resize them, and so on. In this section, we'll discuss some tips for use in design windows.

The first trick is useful for figuring out precise distances between objects while looking at them in the design window. If you select an object, then hold down the Option key, you'll see the exact distances from the borders of the object to the edges of the window (see Figure 1).

But wait, that's not all. By moving the mouse pointer while holding down Option, you can have Interface Builder show you the distance between objects, rather than just the distance to the window edges. In Figure 2, the pointer is on the static text object, and the window shows the distances from the selection to each edge of that object.

You can use another Interface Builder feature to make objects automatically resize or reposition themselves when you change the size of their enclosing window. For example, let's say you want to preserve the proportional distance between the three buttons in the window above: if you widen the window, you want the distance between the buttons to increase. To make this happen, you can create springs between the objects. To do this, select each object in turn, open the size inspector, and click that line that you want to become a spring (a proportional relationship that changes automatically when you resize the window). Figure 3 shows what this looks like for the "Stop" button in the window above: we've clicked on its connection lines to make them into springs. We'll do the same for all 3 buttons.

Now, when we resize the window, if we hold down the Control key, the springs will cause the distances between objects to change proportionally. If we want the springs to be ignored, we can just resize without holding down Control.

Speaking of the size inspector, it's even smarter than you might have realized. You can type math expressions into the coordinate fields and let Interface Builder evaluate them for you. For example, if you want to add 32 pixels to an object's width, you can just click in the w field, select after the current value, then type "+32" and press return. Neato! Apple even provides code to help you implement this trick in your own fields. Take a look at /Developer/Examples/InterfaceBuilder/BusyPalette for details.

Another fun trick you can use with design windows is to see all the rectangles that Interface Builder uses to determine distances between objects. By using the Layout --> Show Layout Rectangles menu item, or just pressing command-L, you can see all the layout rectangles at once, as shown in Figure 4.

Interface Builder tips aren't all about layout. For example, there's a quick way to set the tab order for objects in the window. You'll want to do this to allow users to tab from one text field to the next. The tab order starts with the initial first responder, and continues from there by following each object's nextKeyView field.

To start setting the order, select the object you want to be the initial first responder and choose Layout --> Keyboard Navigation --> Make Initial First Responder. Then, to set the tab order, choose Layout --> Keyboard Navigation --> Show Keyboard Check, Control-drag from one object to the next, then click Connect in the connection inspector. That will set the tab connection between the objects. Note that when you have keyboard check turned on, the word tab appears at the bottom left of the window. That reminds you that you can press tab to test the tab order.

Not all the neat tricks are in the design window - here are a couple you can use in the document window. If you click the tiny control on the right side of the window, the object instances are displayed in an outline view, with the number of connections, both into and out of the object. If you click on one of these numbers, the connections appear in the window, as you can see in Figure 5.

You can use this view to delete connections between objects. If you hold down Control and point at a line that connects two objects, the pointer changes to a tiny pair of scissors, and clicking (you guessed it) cuts the connection.

If you just want to learn more about the connected objects, click on the name of the connected field, such as menu or _panel in Figure 5. The connected objects will appear on the screen with a line between them.

You can find more fun and timesaving tips like these by reading the informative FAQ that comes with Interface Builder. Get to the FAQ by choosing FAQ in Interface Builder's Help menu. There's even a sense of humor in the FAQ: in the section on modifier keys, right after the descriptions of what happens if you press Command, Option, and Control, the FAQ tells you that you can use the Left Pedal to disengage the clutch. Cool.

Scott Knaster has been writing about Macs for as long as there have been Macs. Scott's books How To Write Macintosh Software and Macintosh Programming Secrets were required reading for Mac programmers for more than a decade. Scott wrote developer books for General Magic and worked on Mac software for Microsoft. Scott's books have been translated into Japanese and Pascal. Scott has every issue of Mad magazine, which explains a lot.