Databases
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    <p>I will try to explain the value of delegation with one example.</p> <p>Say you have a table; the table will show some rows. Suppose now, you want to customize the way this table react to some event, e.g., the selection of a specific row.</p> <p>One common way of doing this in OOP is subclassing a table base class and overriding some methods there.</p> <p>With delegation, you don't need subclassing the table base class; rather you use the base class and tell it to "forward" some messages to some other object. This is the basic idea.</p> <p>In our example, when the row is clicked, the table base class does not know what do except sending a message to one object that you specify as the delegate to carry through that action.</p> <p>So, one basic advantage of delegation is that you do not need to subclass. Another advantage you have is that a delegate can act as the delegate for several other objects. Indeed, if you have a look at the generic declaration of a delegate method, you will see that the first parameter is the object that is delegating:</p> <pre><code>- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath </code></pre> <p>so when the delegate receives the message, it knows who sent it and with which object it should interact. </p> <p>The example I gave you about the table shows one kind of delegation, which I would not compare to callbacks. Anyway, delegation can be used as well as a kind of advanced calling-back-scheme. </p> <p>Take the class <code>NSURLConnection</code>; it can be used to manage aynchronous communication.</p> <p>Async communication is the typical case where callbacks are used.</p> <p>With <code>NSURLConnection</code>, the delegate pattern is preferred; so, instead of specifying a callback (a function, which has to be a static function, or a static class method), you specify an object. This object implements the methods that a protocol defines (<code>NSURLConnectionDelegate</code> protocol); you can see those as a whole set of callback functions. When the <code>NSURLConnection</code> has some data ready, it will call a method of the interface, e.g., <code>– connection:didReceiveResponse:</code> to notify that it has received the response.</p> <p>In such case, the point is not avoiding subclassing, rather it is a more flexible callback mechanisms (allowing for better encapsulation, basically).</p> <p>I hope this helps clarifying the two concepts...</p>
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    1. POProblem understanding Delegating pattern & callback functions in Objective C
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    1. COThat means object of myViewController is delegating object and TableView is delegate which invokes (delegate method) **didSelectRowAtIndexPath**. Am i getting this right way?
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    2. COThe delegating object is the one that invokes `didSelectRowAtIndexPath`, i.e., the table view; doing this means: sending a message to the delegate, delegating an action. the table view does not know what to do when the user selects a row, so it delegates this action to the delegate object, which is `myViewController`. the delegate (controller) is "in charge" of managing the selection of the row on behalf of the delegating object (table view).
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A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

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