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Is it possible to force the Xcode complier to verify that files referenced in code are valid?

There are multiple points in Cocoa development when you naturally reference a file programmatically via an NSString: 

[UINib nibWithNibName:@"MyNib" bundle:nil];
[UIImage imageNamed:@"MyImage"];
[[UIViewController alloc] initWithNibName:@"MyNib" bundle:nil];

Is there any way at compile time to check is these file references are valid?

Often times after using above methods, I end up changing the name of the referenced file but forget to change the name in code. Everything complies without a problem and it is only when you happen to go to the portion of the app that accesses this file that the bug will reveal itself.

Is there another approach or technique that people use to avoid this sort of error?
Referencing a file name via a string feels very fragile.

bearMountain
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  • Why cant you use if-else construct to check availability of the file at given path? – Anoop Vaidya Jan 04 '13 at 18:29
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    Not really applicable. If a file name has changed, I want to know about this - I don't want and image to be loaded blank. – bearMountain Jan 04 '13 at 18:30
  • AFAIK theres nothing available to let check this while compiling. A safer way would be to use constants. – artey Jan 04 '13 at 18:31
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    Constants would centralize the change, but you would still need to remember to change this constant, and you would be susceptible to typo errors that would be uncaught by the compiler. – bearMountain Jan 04 '13 at 18:33
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    One reason you can't do this is because there's no way to know what files will be accessible at runtime. Just because a file is present on the development system does not mean it will be present when the app is running, and certainly not in the same location. – Hot Licks Jan 04 '13 at 20:25

4 Answers4

4

Warning: This answer is mostly outdated. The general idea is fine but better solutions exist now (e.g. Image assets with a SwiftGen script to generate an enum).

Nibs usually have a class with the same name as the file, e.g.

[[MyViewController alloc] initWithNibName:NSStringFromClassName([MyViewController class]) bundle:nil];

I usually hide it into the controller's init method as [self class].

For image loading, compile-time checks are difficult. Help yourself with macros, first replace the loading method by a simple macro, e.g.

#define LOAD_IMAGE(__IMAGE_NAME__) [UIImage imageNamed:__IMAGE_NAME__]

First thing you should do is to put an assert into this macro and always check that the image was successfully loaded. It's not a compile-time check but it helps to find missing resources.

The second thing is to write a ruby/python/shell/(any scripting language) script that will search your source files for LOAD_IMAGE and check if the file (between parenthesis) exists. As a shell script, it will be very simple (e.g. using grep). You can add this script into your xcode project to be run when compiling. Don't forget to check images referenced by xibs.

However, often you have to create the image name dynamically, e.g. NSString* imageName = [NSString stringWithFormat:@"image_%i", index]. There's no way how you can check this at compile time.

Also don't forget to do the reverse check - don't include image files which are not used anywhere.

Sulthan
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  • Great scripting solution - I hadn't thought of this approach. Though on your first point, `[[MyViewController alloc] init]` actually already searches through your files and loads a nib if it has a name that matches the `MyViewController` class (according to Apple docs). This could save you a little bit of trouble. – bearMountain Jan 04 '13 at 19:22
  • @bearMountain I know about it, had a problem with the default search when inheriting controllers from a base controller. Don't remember exactly the reason but I am using the `[self class]` now. Not a big trouble :) – Sulthan Jan 04 '13 at 20:02
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AutoComplete for [UIImage imageNamed:] by Kent Sutherland.
This provides code completion support within Xcode - a brilliant piece of code. This is working for me in Xcode 4.6: enter image description here

Currently this project does not have support for strings other than imageNamed:. To support those, I will try to write a compile time script. Or maybe I will become bold and try to extend Mr. Sutherland's spectacular work.

bearMountain
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1

Xcode doesn't support this, but if this problem is really biting you then you could use the following hack:

  • Give every in-bundle file a unique prefix (e.g. app__)
  • When you add a file to your project, make sure you first rename it to add this prefix.
  • Your compile time (pre-distribution) check then has two parts: 1) Search through all .m files and enumerate strings that begin with the prefix. You shouldn't have to check if the string is quoted since your prefix is unique. 2) grep project.pbxproj for each string to check if it is included in the bundle.

With some effort, this process can be mostly automated and also optimized, but the above recipe ought to work.

er0
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1

here is a bash script that we use that lists all images on disk but NOT referenced in code. https://gist.github.com/3750087

it would likely be easy to reverse this to check for non-exting images and xibs. Anyways, the script should be a good starting point

Daij-Djan
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