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More on Xcode

Volume Number: 19 (2003)
Issue Number: 9
Column Tag: Programming

Geeting Started

More on Xcode

by Dave Mark

I must say, I am really enjoying digging into Xcode. I'm impressed with what I've seen so far. The bugs I've encountered have mostly been cosmetic and, I assume, easily fixable. My understanding is that the WWDC release is the only Jaguar release and that all fixes and future releases will be Panther-only.

For the moment, I'll stick with the Jaguar version. As soon as a "for public consumption" version of the Panther Xcode makes its way into my hot little hands, I'll shift permanently into Panther mode.

Editor Window Details

Last month's column started off by opening an existing Project Builder project called Sketch.pbxproj in Xcode and updating the target, creating a new target called Sketch (Upgrade). Go ahead and launch Xcode and open the project. If you are starting from scratch, you'll find Sketch.pbxproj in the directory /Developer/Examples/AppKit/Sketch/. Remember, you can open a project by navigating to the right directory and clicking the Open button. Xcode will find the project file for you.

When the project window appears, click and hold on the Build and Debug icon. After a slight pause, a drop-down menu will appear (see Figure 1). The little triangle to the lower right of an Xcode tool icon is your clue that there's a drop-down menu lurking within. Just remember to hold and wait a hitch for the menu to appear.

Figure 1. The Build and Debug drop-down menu.

Go ahead and select Build and Debug from the drop-down menu. Xcode will build and launch a debug-ready version of Sketch and open the debugger window. As you'd expect, the debugging window allows you to control the debugging process.

Use the Dock to bring Sketch to the front. Click on the rectangles icon in the palette, then click and drag out a rectangle in the main window (see Figure 2). Note that the rectangle that appears is not filled.

Figure 2. Dragging out a rectangle with Sketch.

Now go back to the project window and click on the Project Symbols group (the last group in the Groups & Files column). As you saw last month, this "smart group" lists all the symbols in the project. Type init in the search field to reduce the list of symbols (See Figure 3).

Figure 3. Using the search field to find the init method in SKTGraphic.m.

We're looking for the init method in the file SKTGraphic.m. There are two ways to open this file from the listing in the Project Symbols group. We can click on the Editor icon in the toolbar (the cursor is pointing to this icon in Figure 3) to open an editing pane for that file in the Project Window. Alternatively, we can double-click on the line listing the file we want to open that file in a separate editing window. That's the method we're going to use here.

Figure 4 shows the editor window that appeared when I double-clicked on SKTGraphic.m. At the top of the window is the editor toolbar. Just beneath that is the status bar (in Figure 4 it says Sketch (Upgraded)).

Figure 4. A new editing window listing the file SKTGraphic.m.

Below the status bar is the navigation bar. Towards the left edge of the nav bar is a pair of arrows. These act like the left and right arrows in your browser and are used to move between source files. You'll see how this works in a sec.

If you scan to the right side of the nav bar, you'll see an icon showing a pair of overlapping rectangles, a grey one in front of a white one. This is called the counterpart icon. Click on it to switch between a .m and its corresponding .h file. For example, click the counterpart icon to switch to SKTGraphic.h. Note that the left arrow on the left side of the nav bar is now enabled. You can click it to go back to the file SKTGraphic.m. And, as you'd expect, once you click on the left arrow, the right arrow will be enabled so you can go back to SKTGraphic.h. As promised, just like the arrows in your browser.

As you visit different files in your editor window, they are added to a list, sort of a running history. Immediately to the right of the arrows in your nav bar is a popup listing all the files in this history list. Select a file name and the editor edits that file. Makes sense. The tiny dogear icon immediately to the left of the file name is a dirty flag. If the file is dirty (if it has changed since the last save) the icon is grey. Save the file and it returns to white.

Just to the right of the file name is a colon (":") followed by the current line number (either the beginning of a selection, or the line holding the insertion point). If you want to go to a specific line in a file, you can trial and error it, clicking around using the line number in the nav bar to help you home in on the right line. Or you can select Go to Line... from the Find menu (Command-L) and use that interface to select a specific line or range of lines (See Figure 5).

Figure 5. The Go to Line... command from the Find menu.

Also in the nav bar, just to the right of the file popup menu, lies the function/method popup. As you'd expect, this popup lists all the functions in the current file. Click anywhere inside a function and that function is shown in the popup title. Click on the popup and all the functions/methods in the file are listed in the order in which they appear. Option-click and the functions are listed in alphabetical order, separated by implementation. Give it a try. You'll get it right away.

Next over to the right is the counterpart icon (which we discussed above) followed immediately by the included files popup (it looks like a #) which lets you edit the tree of included files. Figure 6 shows the included files popup for SKTGraphic.m.

Figure 6. The included files popup menu.

To the lower right of the included files popup (at the top of the scroll bar) is the split view toggle. Click on the toggle to create a split in the editing window. Click the toggle again to remove the split. Once you create a split, the split resize control appears between the upper and lower scroll bars. To move the split, just drag this control (See Figure 7). Note that in the current Jaguar release (and presumably the only Jaguar release) of Xcode, the split resize control does not get drawn when you first create a split. Just resize the window a tiny bit and the control will appear.

Figure 7. Dragging the split resize control.

Fix and Continue

One of my favorite Xcode features is Fix-and-Continue. With Mac OS X's built-in support for dynamic linking, you can actually modify your code while it is running and watch the change come to life. Really.

So let's try this out. When you played with Sketch earlier in the column, you dragged out a rectangle and saw that the result was unfilled. If you look through the source code, you'll find that the fill color is white, but the setDrawFill: method is called with the parameter NO. In SKTGraphic.m, here's the init method:

- (id)init {
    self = [super init];
    if (self) {
        _document = nil;
        [self setBounds:NSMakeRect(0.0, 0.0, 1.0, 1.0)];
        [self setFillColor:[NSColor whiteColor]];
        [self setDrawsFill:NO];
        [self setStrokeColor:[NSColor blackColor]];
        [self setDrawsStroke:YES];
        [self setStrokeLineWidth:1.0];
        _origBounds = NSZeroRect;
        _gFlags.manipulatingBounds = NO;
    return self;

Pay special attention to lines 6 and 7, which correspond to lines 20 and 21 in the file. If you haven't already, launch Sketch in the debugger. You can click on the Debug spray can in the editing window or debug window's toolbar, or select from the hammer/spraycan icon in the Project Window's toolbar.

Once Sketch launches in debug mode (you can tell the debugger is active because the Terminate and Pause icons will be enabled in the Debug window), drag out a couple of rectangles, just to prove that they are, indeed, unfilled.

Now go back to your editing window for SKTGraphic.m and change line 20 and 21 from:

        [self setFillColor:[NSColor whiteColor]];
        [self setDrawsFill:NO];


        [self setFillColor:[NSColor greenColor]];
        [self setDrawsFill:YES];

Do NOT save. You'll see why in a sec.

Basically, we've changed the fill color from white to green and we've told Sketch that we do want our shapes filled.

Now comes the cool part.

Select Fix from the Debug menu.

Remember not to save!

You'll see a message in the Debug window about compiling and building. Once that settles down, go back to the running Sketch and click and drag out a rectangle. Wait, I've done it for you. Check out Figure 8. As you were expecting, the rectangles are now filled and green.

Figure 8. After the fix is applied, our rects are filled with green. Cool!

Once you are done playing with your new green rects, quit Sketch and rerun it, either as a straight run or via the debugger. Notice that your rectangles are back to being unfilled (you did remember to not save your changes, right?) To me, this is a beautiful way to play with your code. You can make changes, experiment, use Debug/Fix to test out your changes, see what works for you, then save what you want to.

I find dynamic linking fascinating. Fix and Continue works for Objective C, Carbon/C++ or even straight C, so it's available to all Mac OS X APIs and development languages. Though the Xcode team did not create dynamic linking, they did an excellent job rolling it into the environment. Brilliant!

    You may have noticed a scotch-tape dispenser icon in the Debug window with the label Fix. Clicking this icon does the same thing as selecting Fix from the Debug menu. There is a bug (I believe it is fixed in the current Panther release) where the icon is disabled (it just beeps when you click it). Fortunately, the bug does not affect the Fix item in the Debug menu.

Till Next Month...

Whelp, I'm out of space again. <sigh>. There's so much more I want to talk about. Next month, we're going to take the debugger through its paces and we'll also play around with a feature called code completion, one of my very favorite parts of Xcode. See you then...

Dave Mark is a long-time Mac developer and MacTech contributor. Author of more than a dozen books on various Mac-development topics, Dave is all about Xcode these days. Last month's column focused on the basics of opening a Project Builder project, target conversion, and the project window user interface. This month's installment will focus on the editor interface and a demo of fix-and-continue.


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