8: How iTap Tackles the Challenges of Networking in Objective-C

Drawing QR Code JIS X 0510 in Objective-C 8: How iTap Tackles the Challenges of Networking

CHAPTER 8: How iTap Tackles the Challenges of Networking
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are triggered using a two-finger touch. We quickly developed a small state machine for the first version that included all of these features, but thorough testing on all platforms showed that tuning thresholds for the different inputs was difficult but necessary to provide good user experience. To facilitate multitouch gestures, we created a user interface that showed a mock-up of an actual notebook touchpad. In addition to left/right button clicks and two-finger scrolling gestures, we implemented a three-finger downward swipe gesture to activate the virtual keyboard. To provide users with the choice of how to create mouse events, we allow iTap to display a single button or two buttons (left and right). This is not our default configuration for iTap, but Windows users especially sometimes prefer seeing buttons instead of working only with gestures.
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Both USB and Bluetooth are interfaces largely inaccessible from third-party applications. Especially for communicating with other computers in a network, the only option is WiFi. Although iPhone OS 3.0 supports peer-to-peer networking via Bluetooth, this support is mostly limited to networking between iPhones (and iPod touches). The only exception is the tethering option in iPhone OS 3.0, which establishes a network connection between the iPhone and a computer to allow the computer to share the iPhone s Internet connection. Since this network connection is very similar to a WiFi connection from an application s point of view, iTap is able to use it to communicate with the computer. iPhone applications, however, cannot exercise any control over this connection, and hence the burden of setting it is solely on the user. Given these constraints, WiFi remains the most important means of communication between the iPhone and a computer. Getting iTap to work on any WiFi network that users may have at home or at work quickly emerged as our main concern. Our first prototypes simply sent all data using broadcasts, which is an easy way to do prototyping. UDP broadcasts provided a way to test all the usability features of iTap without spending a single hour on configuration or complicated autodiscovery. Broadcasts on the other side quickly emerged to be a big problem for practical use on wireless networks. One of the main reasons is that access points can and will delay sending broadcasts because they try to send them blocked and with less priority. This results in strange behavior when sending mouse movement events; specifically, they start to lag, and this delay makes such an application nearly unusable. An interesting observation was that controlling a computer connected by a cable to the access point where the iPhone was connected through WiFi resulted in very low network delays even when sending everything as broadcasts. But controlling, for example, a
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CHAPTER 8: How iTap Tackles the Challenges of Networking
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notebook computer connected to the same WiFi network instead of by cable immediately had severe latency problems in the order of 20ms to 100ms delays. The solution to this problem was simple; just perform autodiscovery using broadcasts or multicasts and then communicate directly between iTap and its receiver application. Directly in this context means sending data directly to the other peer s IP address.
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iTap needs the iTap receiver to handle data sent from the device through the network and to synthesize input. The nature of supporting more than one platform creates a whole new set of challenges that can be tracked down differently. One approach is of course to develop two separate applications and to optimize the visual appearance and installation process of each application for the respective platform. This essentially doubles the effort required to develop and maintain the application compared to supporting only a single platform. Because we have developed many multiplatform applications in the past, it was no question that we were going to use all the tools, libraries, and possibilities available to create applications looking, installing, and behaving like native ones but also share as many lines of code as possible between the different platforms. The following were the requirements of the iTap receiver with respect to multiplatform development: Easy to install Simple to use (and no alien platform look and feel) Multiplatform (at least Mac OS X and Windows) These requirements set strict limitations on which technologies to use and how to implement a version to be released. Simplicity during the install process already limits how it will be distributed through our web site and how it appears to the user. The Mac OS X version comes as a DMG image where you can simply install the iTap receiver by dragging it to your Applications folder. To enhance user convenience, the Applications folder is already prelinked to the default view of the DMG file. The Windows version is deployed with an installer where we used the Windows Installer XML (WIX) toolkit (http://wix.sourceforge.net/) originally developed by Microsoft to create a proper Windows Installer .msi file. The WIX toolkit additionally provides features to add firewall exceptions to the Windows integrated firewall, which proved to be a very important feature to reduce the number and complexity of support requests. Qt was our choice for the GUI development. It provides all the features required for welldesigned applications that are simple to roll out. We also both already had experience developing applications based on Qt from past business software projects that came in handy.
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