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Learn Objective C on the Mac phần 5

bạn nhận được với bộ nhớ mới phân bổ. Khi việc phân bổ và các bước khởi tạo được thực hiện, chúng ta nói rằng một trường hợp đối tượng mới đã được tạo ra.Bởi vì các biến địa phương của một đối tượng cụ thể với trường hợp của đối tượng, chúng ta gọi là các biến dụ, thường rút ngắn "Ivars." | CHAPTER 7 More About Xcode 125 a common myth that programmers are loners but sometimes you do need to hear a voice that s different from the voices in your head. Figure 7-28. Setting a breakpoint Now select Run Debug to run your program. Your program should stop at the breakpoint as shown in Figure 7-29. Notice the red arrow pointing at a line of code. This is like the sign on the mall map that says You are here. Figure 7-29. You are here. 126 CHAPTER 7 More About Xcode The status line at the bottom of the Xcode window says GDB Stopped at breakpoint. You ll see that you ve grown a new control strip above the navigation bar shown in Figure 7-30. Figure 7-30. Debugger controls Starting from the left the first pop-up lets you select which thread you want to look at. You won t need to bother with threaded programming for a while so you can ignore this for now. NOTE__ Threaded programming Is programming with multiple streams of execution happening at the same time and it is very difficult to do correctly. Threaded programming often creates bugs that are incredibly difficult to chase down. If anyone tells you threaded programming is easy they re either deluded or trying to sell you something. The next control looks like a breakpoint and it toggles all breakpoints on or off. You might decide Hey I think I fixed everything. Rather than deleting all your breakpoints you can just turn them off and let the program run. When you discover another bug you can turn them back on and get back to debugging. The next four controls deal with what happens next as far as program control goes. The first looks like the play button from a CD player. Recall those If not maybe ask your parents. This is the continue button you could also us the shortcut TP. After you click it the program runs until it hits a breakpoint finishes or crashes. The next control which looks like a dot with someone jumping over it is the step over .