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POSending Data via Message Object Using NSKeyedArchiver
 

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  1. POSending Data via Message Object Using NSKeyedArchiver
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    <p>I'm implementing a multiplayer game where I have to send data between players using:</p> <pre><code> [self sendData:data mode:GKMatchSendDataReliable]; </code></pre> <p>Instead of using multiple c-structs like in this tutorial (<a href="http://www.raywenderlich.com/3325/how-to-make-a-simple-multiplayer-game-with-game-center-tutorial-part-22" rel="nofollow">http://www.raywenderlich.com/3325/how-to-make-a-simple-multiplayer-game-with-game-center-tutorial-part-22</a>), I created a Message object and a subclass of Message called Submessage. The subclasses are created so I avoid sending unnecessary variables in each message, to minimize the size of each packet sent. I then used NSCoding to encode and decode the messages. </p> <p>The classes look something like the following:</p> <p><strong>Message.h</strong></p> <pre><code> @interface Message : NSObject &lt;NSCoding&gt; @property int messageType; - (void)encodeWithCoder:(NSCoder*)coder; - (id)initWithCoder:(NSCoder*)coder; </code></pre> <p><strong>Message Coder Methods</strong></p> <pre><code>-(void) encodeWithCoder:(NSCoder *)coder{ [coder encodeInt:messageType forKey:@"messageType"]; } -(id)initWithCoder:(NSCoder *)coder { self = [super init]; messageType = [coder decodeIntForKey:@"messageType"]; return self; } </code></pre> <p><strong>Submessage.h</strong></p> <pre><code> @interface Submessage : Message &lt;NSCoding&gt; @property float additionalParameter1; - (void)encodeWithCoder:(NSCoder*)coder; - (id)initWithCoder:(NSCoder*)coder; </code></pre> <p><strong>Submessage Coder Methods</strong></p> <pre><code>- (void)encodeWithCoder:(NSCoder *)coder{ [super encodeWithCoder:coder]; [coder encodeFloat:additionalParameter1 forKey:@"float"]; } - (id)initWithCoder:(NSCoder *)coder { self = [super init]; [self initWithCoder:coder]; floatParameter1 = [coder decodeFloatForKey:@"floatParameter1"]; return self; } </code></pre> <p>After I receive the data, I use the following method to unarchive it:</p> <pre><code> Message *thisMessage = [NSKeyedUnarchiver unarchiveObjectWithData:data]; </code></pre> <p>However, this doesn't work when I'm sending Submessage. How can I determine whether data is of type Message or Submessage? How should I implement this so that it would work like in the c-struct case?</p>
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    1. COBy _doesn't work_, do you mean to say that `[NSKeyedUnarchiver unarchiveObjectWithData:[NSKeyedArchiver archivedDataWithRootObject:submessage]]` returns an instance of `Message` instead of `Submessage` ?
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    2. COAlso you may want to show how you implemented your `initWithCoder` methods.
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    3. COYou are concerned about the size of the packet, yet you are sending archived data. Have you checked how huge keyed archives get due to the overhead? Instead of 8 bytes for a point you may be sending over 200 bytes.
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