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 <a name="Dynamically-registering-methods"></a>
 <div class="header">
 <p>
 Next: <a href="Forwarding-hook.html#Forwarding-hook" accesskey="n" rel="next">Forwarding hook</a>, Up: <a href="Messaging-with-the-GNU-Objective_002dC-runtime.html#Messaging-with-the-GNU-Objective_002dC-runtime" accesskey="u" rel="up">Messaging with the GNU Objective-C runtime</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="Dynamically-registering-methods-1"></a>
 <h4 class="subsection">8.10.1 Dynamically registering methods</h4>

 <p>If <code>objc_msg_lookup()</code> does not find a suitable method
 implementation, because the receiver does not implement the required
 method, it tries to see if the class can dynamically register the
 method.
 </p>
 <p>To do so, the runtime checks if the class of the receiver implements
 the method
 </p>
 <div class="smallexample">
 <pre class="smallexample">+ (BOOL) resolveInstanceMethod: (SEL)selector;
 </pre></div>

 <p>in the case of an instance method, or
 </p>
 <div class="smallexample">
 <pre class="smallexample">+ (BOOL) resolveClassMethod: (SEL)selector;
 </pre></div>

 <p>in the case of a class method.  If the class implements it, the
 runtime invokes it, passing as argument the selector of the original
 method, and if it returns <code>YES</code>, the runtime tries the lookup
 again, which could now succeed if a matching method was added
 dynamically by <code>+resolveInstanceMethod:</code> or
 <code>+resolveClassMethod:</code>.
 </p>
 <p>This allows classes to dynamically register methods (by adding them to
 the class using <code>class_addMethod</code>) when they are first called.
 To do so, a class should implement <code>+resolveInstanceMethod:</code> (or,
 depending on the case, <code>+resolveClassMethod:</code>) and have it
 recognize the selectors of methods that can be registered dynamically
 at runtime, register them, and return <code>YES</code>.  It should return
 <code>NO</code> for methods that it does not dynamically registered at
 runtime.
 </p>
 <p>If <code>+resolveInstanceMethod:</code> (or <code>+resolveClassMethod:</code>) is
 not implemented or returns <code>NO</code>, the runtime then tries the
 forwarding hook.
 </p>
 <p>Support for <code>+resolveInstanceMethod:</code> and
 <code>resolveClassMethod:</code> was added to the GNU Objective-C runtime in
 GCC version 4.6.
 </p>


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	<a name="Dynamically-registering-methods"></a>
	<div class="header">
	<p>
	Next: <a href="Forwarding-hook.html#Forwarding-hook" accesskey="n" rel="next">Forwarding hook</a>, Up: <a href="Messaging-with-the-GNU-Objective_002dC-runtime.html#Messaging-with-the-GNU-Objective_002dC-runtime" accesskey="u" rel="up">Messaging with the GNU Objective-C runtime</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="Dynamically-registering-methods-1"></a>
	<h4 class="subsection">8.10.1 Dynamically registering methods</h4>

	<p>If <code>objc_msg_lookup()</code> does not find a suitable method
	implementation, because the receiver does not implement the required
	method, it tries to see if the class can dynamically register the
	method.
	</p>
	<p>To do so, the runtime checks if the class of the receiver implements
	the method
	</p>
	<div class="smallexample">
	<pre class="smallexample">+ (BOOL) resolveInstanceMethod: (SEL)selector;
	</pre></div>

	<p>in the case of an instance method, or
	</p>
	<div class="smallexample">
	<pre class="smallexample">+ (BOOL) resolveClassMethod: (SEL)selector;
	</pre></div>

	<p>in the case of a class method. If the class implements it, the
	runtime invokes it, passing as argument the selector of the original
	method, and if it returns <code>YES</code>, the runtime tries the lookup
	again, which could now succeed if a matching method was added
	dynamically by <code>+resolveInstanceMethod:</code> or
	<code>+resolveClassMethod:</code>.
	</p>
	<p>This allows classes to dynamically register methods (by adding them to
	the class using <code>class_addMethod</code>) when they are first called.
	To do so, a class should implement <code>+resolveInstanceMethod:</code> (or,
	depending on the case, <code>+resolveClassMethod:</code>) and have it
	recognize the selectors of methods that can be registered dynamically
	at runtime, register them, and return <code>YES</code>. It should return
	<code>NO</code> for methods that it does not dynamically registered at
	runtime.
	</p>
	<p>If <code>+resolveInstanceMethod:</code> (or <code>+resolveClassMethod:</code>) is
	not implemented or returns <code>NO</code>, the runtime then tries the
	forwarding hook.
	</p>
	<p>Support for <code>+resolveInstanceMethod:</code> and
	<code>resolveClassMethod:</code> was added to the GNU Objective-C runtime in
	GCC version 4.6.
	</p>



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