When you define a variable outside the scope of a function, that variable’s value is actually written into your executable file. This means you can only use a constant value. Since you don’t know everything about the runtime environment at compile time (which classes are available, what is their structure, etc.), you cannot create objective c objects until runtime, with the exception of constant strings, which are given a specific structure and guaranteed to stay that way. What you should do is initialize the variable to nil and use +initialize to create your image. initialize is a class method which will be called before any other method is called on your class.
Example:
NSImage *imageSegment = nil;
+ (void)initialize {
if(!imageSegment)
imageSegment = [[NSImage alloc] initWithContentsOfFile:@”/User/asd.jpg”];
}
– (id)init {
self = [super init];
if (self) {
// Initialization code here.
}
return self;
}
A global variable has to be initialized to a constant value, like 4 or 0.0 or @”constant string” or nil. A object constructor, such as init, does not return a constant value.
If you want to have a global variable, you should initialize it to nil and then return it using a class method:
NSImage *segment = nil;
+ (NSImage *)imageSegment
{
if (segment == nil) segment = [[NSImage alloc] initWithContentsOfFile:@”/user/asd.jpg”];
return segment;
}