Question

I have a sorting comparator which I need to use in a few different ViewControllers so I’m trying to keep it in a separate file. I’ve read I should be able to put the sorting block in a separate file, but which ever method I try I seem to get “unrecognized selector sent to instance”. The code I have is:

#import <Foundation/Foundation.h>

typedef NSComparator (^IntBlock)(id obj1, id obj2);

@interface Utils : NSObject {
    NSComparator SortObjNameComparer;
    NSComparator SortObjPriceComparer;
}
@property (readwrite, copy) NSComparator SortObjNameComparer;
@property (readwrite, copy) NSComparator SortObjPriceComparer;

To sort this I’m using

Utils *comp = [[Utils alloc] init];
if(segmentedControl.selectedSegmentIndex == 0){
    self.productArray = [self.productArray sortedArrayUsingComparator:[comp SortObjNameComparer] context:nil];   //EXC_BAD_ACCESS     
} else if(segmentedControl.selectedSegmentIndex == 1){
    self.productArray = [self.productArray sortedArrayUsingComparator:[Utils SortObjPriceComparer]];// EXC_BAD_ACCESS

Is there a clean way to do this?

Answer 1

Another way to do this is to create a C function that returns a block. That way you can create this block wherever you like:

e.g

MyComparator.h

#import <Foundation/Foundation.h>

NSComparator CreateObjNameComparer(void);
NSComparator CreateObjPriceComparer(void);

MyComparator.m

#import MyComparator.h

NSComparator CreateObjNameComparer(void) {
    NSComparator myComparator = ^(id obj1, id obj2) {
        // Your definition here
    };
    return Block_copy(myComparator);
}

NSComparator CreateObjPriceComparer(void) {
    NSComparator myComparator = ^(id obj1, id obj2) {
        // Your definition here
    };
    return Block_copy(myComparator);
}

And then all you need to do it use these is to import the header and use it as:

NSComparator nameComparator = CreateObjNameComparor();
// Use the block
Block_release(nameComparator);

Saves having to go through the whole Object creation and property route.

Note that I’m using the Create naming convention to remind me that I have to release the object myself when I’m done with it.