Writing Mobile Code Essential Software Engineering for Building Mobile Applications [Electronic resources] نسخه متنی

Form Factor

The need to fit comfortably into one's pocket is a key defining characteristic of most mobile devices. This physical constraint is the basis for the mobile device's utility; if it fits in your pocket, it is mobile. Some additional important form-factor considerations are as follows:

The ability to be used in crowded and noisy spaces
This is a reason why speech input is not always a great idea even if it is technically possible. It is also important that a mobile device not be disturbing to those around it (a reason why voice response is not always a great idea). A train full of people arguing with their mobile devices is not a pleasant social environment. Think of having a silent mode or headphones if sound is required for your mobile application.

Single- or two-handed operation
Many devices are intended to be operated by one hand. Most mobile phones meet this criterion. Some are intended to be held in one hand and operated with another. Most PDAs fall into this category. Laptops generally require two hands and a flat surface for efficient usage. Your mobile application should follow whatever paradigm the device imposes on usage; that is, don't build an application that requires two-handed use to get anything useful done if it's going to run on a mobile phone that people typically operate with one hand. This is an important aspect for the usability testing of your application. Another important consideration is the physical environment in which a handheld application is being used. A touch-screen display offers a rich environment for navigating applications, but all too often application designers build and test the user interfaces either running on a desktop-based device emulator or sitting at their desks. This results in user interfaces that are far too small for real-world usage. The real world is full of bumps, jitters, vibrations, and people who want to use their devices while walking down the street or by pressing the screen with their fingers rather than the stylus. Paradoxically, for real-world usage, touch-screen input on small mobile devices often requires larger user interface controls than stationary applications being used on personal computers. It is important to understand whether your application needs to be "one-hand friendly," real-world two-hand "stylus friendly," or "finger friendly" when used with a touch screen while the user is mobile.

No power cords or communications cables for long periods of time
To be effective mobile devices, the devices need to be able to operate untethered for long periods of time. A good rule of thumb is that the devices and the applications running on them should not require being connected to wired power or communication sources more than once a day. How often your application requires the device to be running at full power and how often your application needs to be connected to online data are important design considerations.

These form-factor considerations should strongly influence your design. Engineering creativity is required to solve form-factor problems as well as to adapt software design to different form factors.