In reference to the download package named 2D_Apple_Games_by_Tutorials_3.0, I haven’t checked all project files, but as for Ch. 15, all Xcode project files are corrupted and cannot be opened. For example if you open the package of DropCharge.xcodeproj file under challege4, there’s a file title project.pbxproj. If you open it with a text editor, there are insertions like
I image that these insertions are made as a result of merge conflicts. In sum, these Xcode projects files cannot be opened. It would be nice if you fix them.