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Generator Data Matrix 2d barcode in Objective-C 7: Debugging Your Xcode Projects

CHAPTER 7: Debugging Your Xcode Projects
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Check that you have saved both the .h and .m files, then open Interface Builder by double-clicking MainMenu.xib. Since you are using the AppDelegate object as the Controller, there is no need to add one from the Library as you would have had to do if you had created a dedicated Controller in the Xcode Project Workspace. So let s continue on and build the user interface. First, make the window 480 pixels wide and 360 pixels high (Size Inspector tab). Uncheck the Close, Resize, and Minimize controls in the Attributes Inspector tab this is going to be a simple nonresizable window. Select the Library window and drag out a Color Well, a Vertical Slider, and a Text Field. For the Vertical Slider, set the Height value to 260 pixels, the Minimum Value to 0, the Maximum Value to 255 and the Current value to 128. Set the state to Continuous. Set the Text Field s Alignment to Centered, its width to 40 and leave the Height as 22. Now copy the Vertical Slider and Text Field controls three times (opt-drag is an easy way to do this). The fourth Slider should have a Maximum Value of 1.0 and a Current Value of 0.5. The user interface should look something like Figure 7 3.
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Figure 7 3. The completed ColorPal user interface
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To set the connections, Control-drag from each of the Vertical Sliders and each of the Text Fields in turn in the user interface to the Color Pal App Delegate Controller in the Document window. Choose setNewColor: from the popup in each case (in other words, make eight connections). Now Control-drag from the Color Pal App Delegate Controller to the Color Well, and choose colorWell as the outlet. That completes the work of building the user interface (again, observant or experienced developers will have spotted some omissions, but they are also deliberate). Save the NIB and close Interface Builder, returning to Xcode.
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CHAPTER 7: Debugging Your Xcode Projects
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Running and Debugging the Project
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OK, now Build and Run. There is an immediate problem and the build fails see Figure 7 4.
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Figure 7 4. Syntax error highlighted in the Build Results tab
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This is an easy syntax error to spot (and as I know to my cost, an easy one to make). To see more detail for this error, you can choose the Build Results tab in the Detail pane as shown in Figure 7 4. The messages here spell out the mistake: redValue was not defined in the interface (.h) file, and there is no accessor method for the property redIntValue. Of course, the @synthesize call should be redIntValue, not redValue. Correct that error and Build and Run again. This time the build succeeds and the program runs. It s quickly apparent that there are still some big problems. For one thing, although the pale blue color in the Color Well initially looks right, the Sliders haven t moved to the
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CHAPTER 7: Debugging Your Xcode Projects
positions you might have expected and the Text Fields are blank. Also, nothing happens when you change any of the Sliders or the Text Fields. What s happened here Quit the program and let s look at the code. The first thing that happens in the program is in the awakeFromNib method (Listing 7 3).
Listing 7 3. The awakeFromNib Method - (void)awakeFromNib { [self setValue:[NSNumber [self setValue:[NSNumber [self setValue:[NSNumber [self setValue:[NSNumber [self updateColorWell]; } numberWithInt:51] forKey:@"redIntValue"]; numberWithInt:102] forKey:@"greenIntValue"]; numberWithInt:153] forKey:@"blueIntValue"]; numberWithInt:1.0] forKey:@"alphaIntValue"];
This sets initial values for the red, green, blue and alpha components of the color, and then calls updateColorWell (Listing 7 4):
Listing 7 4. The updateColorWell method - (void)updateColorWell { NSColor *theColor = [NSColor colorWithCalibratedRed:((float)redIntValue/255) green:((float)greenIntValue/255) blue:((float)blueIntValue/255) alpha:(alphaIntValue)]; [colorWell setColor:theColor]; }
The updateColorWell method instantiates an NSColor object with the starting values defined in awakeFromNib, then sets the color of the Color Well to that NSColor. Curious. We know that this must be working, because the Color Well is showing the right color on startup. It s time for some debugging.
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