issue with mixing Objective C and C++ in single file

Question

I am having .mm file, in which i have some c++ function and few line of objective c.

For ex.

void display()
{
....
....
}

void doSomthing()
{
UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 100, 50)];
[button addTarget:??? action:@selector(display) ....]

[rooView addSubView:UIButton];
}

I am not getting the way how i could call display function which defined in same mm file? what will be my addTarget? (self/this not working in my case )

Answer 1

You cannot use @selector() to reference a function, you can only use it to reference an objective-c method.

Further the UIButton class is not capable of performing a function call when it is clicked. It can only perform an objective-c method.

You can however, "wrap" an objective-c method around the function:

- (void)display:(id)sender
{
    display();
}

Allowing this:

[button addTarget:self action:@selector(display:) ....];

But if you are writing your own display() function, then you may as well just put it's contents in the display method.

Answer 2

You need an Objective-C class and some methods to wrap your C++ function calls.

@interface WrapperClass : NSObject

-(void) display;

@end

void display()
{
....
....
}

@implementation WrapperClass

-(void) display
{
    display();
}

@end

static WrapperClass* wrapperObj = nil;

void doSomthing()
{
    if (wrapperObj == nil)
    {
        wrapperObj = [[WrapperClass alloc] init];
    }

    UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(0, 0, 100, 50)];
    [button addTarget: wrapperObj action:@selector(display) forControlEvents: whatever];
    [rooView addSubView:UIButton];
}