NSBundle的使用，注意mainBundle和Custom Bundle的区别

1、[NSBundle mainBundle]，文件夹其实是Group，如左侧的树形文件管理器

Build之后，文件直接就复制到了根目录下，于是读取的方法，应该是这样：

NSString *earth = [[NSBundle mainBundle] pathForResource:@"Brad Cox" ofType:@"png"];

2、使用文件夹的时候，Build结果

依然使用同样的方法，不需要制定文件夹路径

//inDirectory参数可有可无

NSString *earth = [[NSBundle mainBundle] pathForResource:@"Matthijs" ofType:@"png" inDirectory:@"Images/MoreImages"]; 
NSString *earth = [[NSBundle mainBundle] pathForResource:@"Matthijs" ofType:@"png"];

编译之后，mainBundle的资源都是放到RootFolder下，所以，可以直接访问，不要指定内部路径

3、使用其他的Bundle

NSString *resourceBundle = [[NSBundle mainBundle] pathForResource:@"Resources" ofType:@"bundle"];
    NSLog(@"resourceBundle: %@", resourceBundle);
    NSString *earth = [[NSBundlebundleWithPath:resourceBundle] pathForResource:@"Matthijs"ofType:@"jpg"inDirectory:@"Images/MoreImages"];

    NSLog(@"path: %@", earth);   

使用Custom bundle，访问内部的子文件夹，需要指定inDirectory参数，这个mainBundle不同，这是为何？

注意：Since
bundles other than the main bundle can have folders embedded inside them, to access
files inside folders of a bundle other than the main bundle it is best to use the pathFor
Resource:ofType:inDirectory: method of NSBundle to explicitly specify the folder in
which a specific file/resource exists.