为什么我从Xcode收到此警告？ iOS代码似乎很好

Question

This one has me stumped. I'm writing an iPhone app that tracks bus schedules. Users can bookmark their favorite bus stops so they can jump directly to them from the home screen. I manage the list of favorites in my AppDelegate class (unrelated code has been redacted):

@interface AppDelegate : NSObject <UIApplicationDelegate>
+ (BOOL) isInFavorites: (FavoriteStopData*) inStop;
@end

I have a view controller that presents the list of stops for a given bus route and lets users select one to see predicted bus arrival times for that stop in a new view (and maybe add the stop to their list of favorites):

@implementation RouteStopsViewController
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    FavoriteStopData *stopData = [[FavoriteStopData alloc] init];
// ... set various properties in stopData from data in the selected cell
    FavoriteStopViewController *fvc = [[FavoriteStopViewController alloc] initWithNibName:@"FavoriteStopViewController" bundle:nil];
    fvc.stop = stopData;
    fvc.isBookmarked = [AppDelegate isInFavorites:stopData];
    [stopData release];
    [self.navigationController pushViewController:fvc animated:YES];
    [fvc release];
}
@end

The line

fvc.isBookmarked = [AppDelegate isInFavorites:stopData];

gets two warnings:

"'AppDelegate' may not respond to +isInFavorites:"
"Passing argument 1 of 'setIsBookmarked' makes integer from pointer without a cast"

I can't see any reason for Xcode to think '+isInFavorites:' is undefined, yet it does. I've verified that these possible causes for the warning are not in fact the case:

• '+isInFavorites:' is declared in "AppDelegate.h" (as shown above)

• "RouteStopsViewController.m" does #import "AppDelegate.h" (and "FavoriteStopData.h" and "FavoriteStopViewController.h")

• 'isBookmarked' is a public BOOL property on FavoriteStopViewController

• The code is not being munged by some #define macro; when I preprocess "RouteStopsViewController.m", this code is unchanged.

The code behaves correctly, but I REALLY don't want to live with a warning that I must ignore every time the code compiles, and disabling this warning with some #pragma is a road I'd rather not take unless I have to.

I've tried renaming the method name, the variable names, using the method to set a local BOOL variable and then setting the property with that, using a conditional operator (x ? y : z) to make sure I'm passing a BOOL to the property ... nothing works. That first warning never goes away.

Can anyone suggest why Xcode is giving me this warning?

This is with Xcode 4.2 (Build 4C199) and iOS 5 SDK running in the 5.0 iPhone Simulator on a MacBook Pro running Mac OS X 10.6.8 (Snow Leopard).

Answer 1

If the +isInFavorites: method was completely unknown to the compiler then you'd see a warning like +isInFavorites: not found (return type defaults to 'id') .

If you're not seeing that warning then we can assume that the compiler has seen a declaration of that method somewhere . However, the compiler expects this method to return a pointer rather than a BOOL, which is why you're seeing the makes integer from pointer without a cast warning.

Check for any other declarations of an isInFavorites: method in your project. Check for any global variables named AppDelegate that may conflict with your class name. Check for any circular imports between AppDelegate.h and RouteStopsViewController.h. Try renaming your AppDelegate class.

Answer 2

在你的appdelegate.h文件中声明你的isInFavorites方法。

Answer 3

'AppDelegate' may not respond to +isInFavorites:
Passing argument 1 of 'setIsBookmarked' makes integer from pointer without a cast

The first error causes the second. The compiler's confusion on the existence of +isInFavorites: causes the compiler to assume the return type is id

This assumption causes the warning of making integer from pointer without a cast

You really have to focus on the first warning.

Are these the only warnings?

Try changing your AppDelegate.h to

@class FavoriteStopData
@interface AppDelegate : NSObject <UIApplicationDelegate>
+ (BOOL) isInFavorites: (FavoriteStopData*) inStop;
@end

If you still have issues, you might want to consider making this an instance method instead, considering the appDelegate is valid the whole runtime of your app

Answer 4

Found it. Even makes perfect sense ... now that I know exactly where to look.

My project has two targets: Dev for the version I use to test new code, and App for the user-facing version. Each has its own AppDelegate class (and some other duplicates). Code specific to one target or the other goes into either the ./Dev/ or the ./App/ folder. Common code goes into other folders.

Recently I promoted one Dev-specific class to be used in both targets ... but hadn't yet moved the files out of the Dev folder. This was my problematic RouteStopsViewController. My project was compiling the right "AppDelegate.m", but Xcode was finding the 'wrong' (to my thinking) "AppDelegate.h" because it was looking first in the same folder as "RouteStopsViewController.m".

The fix was easy: move RouteStopsViewController out of the Dev-specific folder into one for code shared by both targets. Now Xcode uses the "AppDelegate.m" file it's compiling to find the matching "AppDelegate.h".

I knew at the time I should move that RouteStopsViewController class when I decided to reuse it in the App target, I just didn't get around to it. When it comes to writing code, trust your nose. If it smells funny, it very probably is.