c# create barcode 8: Improving the Design in Objective-C

Printer Quick Response Code in Objective-C 8: Improving the Design

CHAPTER 8: Improving the Design
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Good programming habits are beyond the subject of this book. What I want to stress is that no matter what the complexity of your system, it s easy to get on the wrong track. Stepping back for a moment, what I m really talking about in this book is just sending information from point A to point B and back again. That s what all this External Accessory stuff is about at its core level. What it really comes down to is using the right tool for the job. In general, you have two options. You can do things simply by letting the system (the iPhone OS) take care of things for you. This is what you did in the last chapter. Your other choice is to take more control of the process and do most of the work yourself. At first glance, this second choice might seem pretty stupid. I mean, isn t that why we invented high-level programming languages or advanced operating systems to do the grunt work for us Unfortunately, these conveniences come with a price. There are reasons that you might want to not use these convenience methods and do things the hard way. The first reason is performance. Let s face it; no matter how fast the latest and greatest iPhone executes apps, you re always going to want more. The thing is, the real problem isn t processor speed at all. The problem you re concerned about is latency or the delay in getting things done. What you re really looking for is a way to accurately predict when something will happen. As I talked about earlier, this goes to the heart of real-time processing. You need to know that if an event of interest takes place that it will be handled within predictable time constraints. For your game program this means that, if the player turns the knob to get to a fast moving ball, your program can respond and move it predictably. Note that I didn t say it would get to the ball in time as that wouldn t be fair. Part of the game is for one player to get the other player out of position enough so that, if he can place the ball far enough away, his opponent won t get to it. What you do need is for the game to respond to events the same way each and every time your events occur. What you do not want to see is the player turn the knob and the paddle not move for an instant while the game s run loop is delayed for something else. In your Pong game, from time to time you will turn the knob and the paddle will seem to stick for a short while. This is because the iPhone OS has other things to do such as periodically checking e-mail or push notifications, responding to changes in signal strength from WiFi or the phone network, and so on. Simply put, you re not likely to get absolute real-time performance. When you connect a hardware accessory to an iPhone or iPod touch, even though you have a fast physical interface, the underlying OS has to do its job, at the same time creating overhead that slows things down. This impacts performance. I mentioned that there were other reasons for not using the conveniences of modern operating systems and programming languages; so what are they
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CHAPTER 8: Improving the Design
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Security Concerns
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What might possibly be the most important reason of all is data security. Before going on, I ll point out that security is boring, especially for the new accessory developer. In most cases, especially early on, it s not really a concern unless you re developing for business applications. So, if you re strictly into gaming or an area where you feel security isn t an issue, you can skip this section and come back later if needed. Consider again Figure 8 1 and your code from the last chapter. When your game controller object (software) is notified that a new position is available for the paddle you packed that data into a dictionary object and sent out another notification. On the other end inside your view controller you read the notification, pulled out the data (position byte), and moved the paddle. But what happened between the time you sent the notification and when you received it The fact is that you don t know. Look again at the potTurned method from your viewController.
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-(void) potTurned:(NSNotification *)notification { NSLog(@"Pot Turned"); NSNumber *position = [[notification userInfo] objectForKey:@"parameter"]; int i = [position intValue]; NSLog(@"Position Received = %d",i); i = (-i + 256); float j = (float)i * (320.0/246.0); CGPoint xLocation = CGPointMake(j,playerPaddle.center.y); playerPaddle.center = xLocation; if (playerPaddle.center.x > (self.view.bounds.size.width /2)) if (playerPaddle.center.x > (self.view.bounds.size.width /2)+101) playerPaddle.image = playerPaddleRightUp; else playerPaddle.image = playerPaddleRight; else if (playerPaddle.center.x < (self.view.bounds.size.width /2)-101) playerPaddle.image = playerPaddleLeftUp; else playerPaddle.image = playerPaddleLeft; }
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Can you count all the places you used the position information First, there s the userInfo dictionary object. From there, you extract the position and put it into an NSNumber using the key parameter . From the NSNumber, you need an integer value so you convert it using the intValue method. But the position of the paddle is a floatingpoint number so there s another conversion. Then, you have to create a point using GCPointMake so you can use the x position to set where you want the paddle to be relocated.
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