CODEWITHSUNDEEP
objective-c
Chris G.
Chris G.

Reputation: 25974

Why use Message Forwarding

Why would you use Message Forwarding in Objective-c. Also when using it, you need to call the Surragate method with performSelector? I am thinking you have a lot of knowledge when you are coding this, why would you need Message Forwarding. I am reading that this is Obj-c multiple inheritance - but I don't see it like this, it is just another object attached to an object.

Hope you know and have a pratical example

Thanks

Upvotes: 0

Views: 155

Answers (1)

matt
matt

Reputation: 535547

See my discussion at the end of this section: http://www.apeth.com/iOSBook/ch25.html#_uitabbar

Here I have interposed my own object as the data source for one of Apple's table views. I don't know how the table view works (it's Apple's) and I don't know what their data source does (it's Apple's). So I substitute my own data source but I keep Apple's, and any messages that I don't handle that arrive at my data source are passed on to Apple's. Thus in a sense I have made my data source "inherit" from Apple's.

@implementation MyDataSource

- (id)forwardingTargetForSelector:(SEL)aSelector {
    if ([self.originalDataSource respondsToSelector: aSelector])
        return self.originalDataSource;
    return [super forwardingTargetForSelector:aSelector];
}

- (NSInteger)tableView:(UITableView *)tv numberOfRowsInSection:(NSInteger)sec {
    // this is just to quiet the compiler
    return [self.originalDataSource tableView:tv numberOfRowsInSection:sec];
}

- (UITableViewCell *)tableView:(UITableView *)tv cellForRowAtIndexPath:(NSIndexPath *)ip {
    // this is why we are here: my tweaks
    UITableViewCell* cell = [self.originalDataSource tableView:tv cellForRowAtIndexPath:ip];
    cell.textLabel.font = [UIFont fontWithName:@"GillSans-Bold" size:14];
    return cell;
}

@end

Upvotes: 3

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