27€ Loading Data From the Main Bundle

It is highly recommended that you give a unique name to each resource

inside your bundles. For instance, it is not good practice to have a file

named Default.png in more than one place inside your main bundle.

Different ways of loading a resource from a bundle could then yield

different results. As a result, make sure you give unique names to your

files inside any bundle, regardless of whether it is the main bundle or a

custom bundle that you've created (see Recipe 1.26).



Discussion

To access the main bundle, we can use the mainBundle class method of the NSBundle

class. Bundles are all of type NSBundle and once you have an instance of a bundle, you

can load resources from that bundle.

Every app's main bundle has a flat hierarchy on disk when it is compiled

for submission to App Store. That means all the files that get wrapped

up in your app bundle will be placed on the root folder of the main

bundle. In other words, the main bundle has only one folder, the root

folder, and all files and resources are stored in that folder. Even if you

have a folder on disk with a few images in it and drag and drop it into

Xcode, only the files in that folder will be placed in the main bundle's

file hierarchy, not the folder itself.



For instance, let's say that you have an image called AlanSugar.png sitting on your

desktop. Simply drag and drop it into Xcode. At this point, Xcode will display a dialog

to you, asking you which project this file has to be added to and whether you want this

file to be copied over to the project's folder, if need be. This dialog will look similar to

that shown in Figure 1-34.



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Figure 1-34. Xcode asking which project a file has to be added to



In this dialog, make sure that the "Copy items into destination group's folder (if needed)" item is selected. This will copy the file that you drop into Xcode to the target

app's folder. Now, if you delete the file on your desktop, it won't get deleted from your

project because your project has its own copy. It's generally good practice to do this

unless for specific reasons you decide not to (and I've experienced many of these reasons

myself). After you drag and drop the file, the file AlanSugar.png is in the project's main

bundle and you can retrieve its path in this way:

- (BOOL)

application:(UIApplication *)application

didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{

NSString *alanSugarFilePath =

[[NSBundle mainBundle] pathForResource:@"AlanSugar"

ofType:@"png"];

if ([alanSugarFilePath length] > 0){

UIImage *image = [UIImage imageWithContentsOfFile:alanSugarFilePath];

if (image != nil){

NSLog(@"Successfully loaded the file as an image.");

} else {

NSLog(@"Failed to load the file as an image.");

}

} else {

NSLog(@"Could not find this file in the main bundle.");



1.27 Loading Data From the Main Bundle | 95



}

self.window = [[UIWindow alloc] initWithFrame:

[[UIScreen mainScreen] bounds]];

self.window.backgroundColor = [UIColor whiteColor];

[self.window makeKeyAndVisible];

return YES;

}



The output of the pathForResource:ofType: method of NSBundle will be either a valid

path or nil if the specified resource cannot be found in the target bundle. So after you

call this method, it is best to check whether the path could actually be retrieved. If so,

the code shown passes the path of the file to the UIImage class in order to load the

AlanSugar.png file into memory as an image.

Similarly, if you wanted to load the data of that file into memory, instead of retrieving

this image as an image object, you could use the NSData class:

- (BOOL)

application:(UIApplication *)application

didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{

NSString *alanSugarFilePath =

[[NSBundle mainBundle] pathForResource:@"AlanSugar"

ofType:@"png"];

if ([alanSugarFilePath length] > 0){

NSError *readError = nil;

NSData *dataForFile =

[[NSData alloc] initWithContentsOfFile:alanSugarFilePath

options:NSMappedRead

error:&readError];

if (readError == nil &&

dataForFile != nil){

NSLog(@"Successfully loaded the data.");

} else if (readError == nil &&

dataForFile == nil){

NSLog(@"No data could be loaded.");

} else {

NSLog(@"An error occured while loading data. Error = %@", readError);

}

} else {

NSLog(@"Could not find this file in the main bundle.");

}

self.window = [[UIWindow alloc] initWithFrame:

[[UIScreen mainScreen] bounds]];

self.window.backgroundColor = [UIColor whiteColor];

[self.window makeKeyAndVisible];



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}



return YES;



See Also

XXX



1.28 Loading Data From Other Bundles

Problem

You have included a few images or other resources in a separate bundle inside your

main bundle and you would like to access those resources at run time.



Solution

Find the path to your bundle at run time using the pathForResource:ofType: method

of your your main bundle. Once you have the path to your bundle, simply access it

using the bundleWithPath: class method of NSBundle.

Before continuing with this recipe, please follow the instructions in

Recipe 1.26 to create a bundle called Resources.bundle and place it inside

your main bundle.



Discussion

If you have followed the instructions in Recipe 1.26, you now have a bundle called

Resources.bundle inside this bundle you have a folder called Images. Let's now put an

image inside this folder. After I placed an image called AlanSugar.png into the bundle

Figure 1-35 shows what the bundle contains.



1.28 Loading Data From Other Bundles | 97



Figure 1-35. Placing an image inside the bundle which we created before



Since the Resources.bundle is added to our app's main bundle, we will need to use the

main bundle in order to find the path to our Resources.bundle. Once that is done, we

can directly access the files (only AlanSugar.png right now) inside this bundle. 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.

- (BOOL)

application:(UIApplication *)application

didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{

NSString *resourcesBundlePath =

[[NSBundle mainBundle] pathForResource:@"Resources"

ofType:@"bundle"];

if ([resourcesBundlePath length] > 0){

NSBundle *resourcesBundle = [NSBundle bundleWithPath:resourcesBundlePath];

if (resourcesBundle != nil){

NSString *pathToAlanSugarImage =

[resourcesBundle pathForResource:@"AlanSugar"

ofType:@"png"

inDirectory:@"Images"];

if ([pathToAlanSugarImage length] > 0){



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