It's important NOT to assume that NSString paths will always work if you construct them yourself. This bit me today. As it has many other times in the past.

gistfile1.m

// In both versions, we're feeding a string to the NSFileManager method, but only the second one succeeds. In the debugger console, they both appeared with the file:// so it was a bit difficult to debug. Of course, I'd momentarily forgot about every. other. time. it has happened.

// Version 1
- (BOOL)fileExistsInCaches:(NSString *)filename
{
    NSString *path = [NSString stringWithFormat:@"%@%@",[self cacheDirectory],filename];
    // path = file://Users/mthongvanh/etc/etc/etc
    return [[NSFileManager defaultManager] fileExistsAtPath:path];
}

// Version 2
- (BOOL)fileExistsInCaches:(NSString *)filename
{
    NSString *path = [NSString stringWithFormat:@"%@%@",[self cacheDirectory],filename];
    NSURL *pathURL = [NSURL URLWithString:path];
    // pathURL = /Users/mthongvanh/etc/etc
    return [[NSFileManager defaultManager] fileExistsAtPath:pathURL.path];
}