Int or NSInteger as object for method argument. Ob

问题:

I'm having some trouble passing a number as an argument for a method:

- (void)meth2:(int)next_int;

And to call that method I need this:

int next_int = 1;
[self performSelectorOnMainThread:@selector(meth2:) withObject:next_int waitUntilDone:NO];
//update next_int and call meth2 again

at this point, I get a "pointer from integer without a cast" error and would happen the same with a NSInteger. An NSNumber is not useful because it's immutable and I need to change the value constantly. Any idea how can I do this?

Thanks.

回答1:

If you're just trying to call the method, you could use the standard syntax:

[self meth2:next_int];

If you really need to use the performSelectorOnMainThread: you could wrap the number in an NSNumber for the call. You say you can't do this because you need to change the number, but you can just pull an int out and change that:

[self performSelectorOnMainThread:@selector(meth2:) withObject:[NSNumber numberWithInt:next_int] waitUntilDone:NO];
// ... later ...
- (void)meth2:(NSNumber *)number {
  int myInt = [number intValue];
  // do stuff with myInt
}

But maybe you mean that you want to get the value of the number as an output from your call to meth2. If that's what you mean, then you could pass in a double pointer so you can receive a new object back:

- (void)meth2:(NSNumber **)number {
  int myInt = [*number intValue];
  // do stuff with myInt
  *number = [NSNumber numberWithInt:myInt];
}
// The caller can now operate like this:
NSNumber *number = [NSNumber numberWithInt:next_int];
[self performSelectorOnMainThread:@selector(meth2:) withObject:&number waitUntilDone:YES];
int returnInt = [*number intValue];

Of course, that's not really thread-safe, so if you're doing stuff with multiple threads, I would advise using the @synchronized keyword for access to multi-thread-accessed variables, or setting up atomic properties (i.e. properties not declared as nonatomic).

Also, meth is bad for you!! haha

回答2:

Wrap the integer in an NSNumber before passing it:

int next_int = 1
NSNumber *theNumber = [NSNumber numberWithInt:next_int];
[self performSelectorOnMainThread:@selector(meth2:) withObject:theNumber waitUntilDone:NO];

Then your -meth2: method could look something like this:

- (void)meth2:(NSNumber*)theNumber
{
    int next_int = [theNumber intValue];
    // do whatever
}

回答3:

It's a bit of a hack, but this works under ARC:

int next_int = 1;
[self performSelectorOnMainThread:@selector(meth2:) 
                       withObject:(__bridge id)(void*)next_int 
                    waitUntilDone:NO];

The __bridge keyword will tell the compiler to ignore reference counting under ARC, but it requires a pointer, so you first have to cast the int to a C style void pointer. When your method receives the message it will treat that object pointer as if it's an integer.

Note: If you can change the method to take an NSNumber instead of an integer, then that would be the "proper" fix. Unfortunately that's not always possible.

回答4:

You can't use next_int as the withObject: because it's not an Object.

Change your call to:

[self performSelectorOnMainThread:@selector(meth2:) 
      withObject:[NSNumber numberWithInt:next_int] waitUntilDone:NO];

EDIT: And change meth2 to expect an NSNumber instead of an int.