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苹果iphone如何运行-A（转贴）
(2008-01-09 11:31:15)
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Then, Jobs touched the screen. Suddenly, the featureless rectangle became an interactive surface. Jobs placed a fingertip on an on-screen arrow and slid it from left to right. When his finger moved, the arrow moved with it, unlocking the phone. To some people, this interaction between a human finger and an on-screen image -- and its effect on the iPhone's behavior -- was more amazing than all of its other features combined.
And those features are plentiful. In some ways, the iPhone is more like a palmtop computer than a cellular phone. As with many smartphones, you can use it to make and receive calls, watch movies, listen to music, browse the Web, and send and receive e-mail and text messages. You can also take pictures with a built-in camera, import photos from your computer and organize them all using the iPhone's software. Although it's not a turn-by-turn GPS receiver, the iPhone also lets you view map and satellite data from Google Maps, including overlays of nearby businesses.?/P>
A modifie璬 version of the Macintosh OS X operating system, also used on Apple desktop and laptop computers, lets you interact with all of these applications. It displays icons for each application on the iPhone's screen. It also manages battery power and system security. The operating system synchs the phone with your computer, a process that requires a dock much like the one used to synch an iPod. It also lets you multitask and move through multiple open applications, just like you can on a laptop or desktop computer.
But instead of using a mouse or a physical keyboard, the iPhone uses virtual buttons and controls that appear on its screen. This isn't really a new phenomenon -- touch screens have been part of everything from self-checkout kiosks to smartphones for years. But the iPhone's touch-screen is a little different from many of the others currently on the market. When you touch the screen on a PDA or a Nintendo DS, you typically use a slender, pointed stylus. The iPhone, on the other hand, requires you to use your fingers. It can also detect multiple touch points simultaneously, which many existing touch-screens cannot do.
This article will explore exactly how the iPhone's touch-screen carries instructions from your fingertips to the phone's internal circuitry. We'll also look at the iPhone's features, its hardware and how it compares to smartphones and other electronic devices.
The iPhone Touch-screen
Electronic devices can use lots of different methods to detect a person's input on a touch-screen. Most of them use sensors and circuitry to monitor changes in a particular state. Many, including the iPhone, monitor changes in electrical current. Others monitor changes in the reflection of waves. These can be sound waves or beams of near-infrared light. A few systems use transducers to measure changes in vibration caused when your finger hits the screen's surface or cameras to monitor changes in light and shadow.
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Image courtesy Consumer Guide Products The Nintendo DS, Palm Treo and Logitech Harmony Remote Control all use touch-screen technology. |
The basic idea is pretty simple -- when you place your finger or a stylus on the screen, it changes the state that the device is monitoring. In screens that rely on sound or light waves, your finger physically blocks or reflects some of the waves. Capacitive touch-screens use a layer of capacitive material to hold an electrical charge; touching the screen changes the amount of charge at a specific point of contact. In resistive screens, the pressure from your finger causes conductive and resistive layers of circuitry to touch each other, changing the circuits' resistance.
Most of the time, these systems are good at detecting the location of exactly one touch. If you try to touch the screen in several places at once, the results can be erratic. Some screens simply disregard all touches after the first one. Others can detect simultaneous touches, but their software can't calculate the location of each one accurately. There are several reasons for this, including:
- Many systems detect changes along an axis or in a specific direction instead of at each point on the screen.
- Some screens rely on system-wide averages to determine touch locations.
- Some systems take measurements by first establishing a baseline. When you touch the screen, you create a new baseline. Adding another touch causes the system to take a measurement using the wrong baseline as a starting point.
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The Apple iPhone is different -- many of the elements of its
multi-touch user interface require you to touch
multiple points on the screen simultaneously. For example, you can
zoom in to Web pages or
pictures by placing your thumb and finger on the screen and
spreading them apart. To zoom back out, you can pinch your thumb
and finger together. The iPhone's touch screen is able to respond
to both touch points and their movements simultaneously. We'll look
at exactly how the iPhone does this in the next section.
Multi-touch Systems
To allow people to use touch commands that require multiple fingers, the iPhone uses a new arrangement of existing technology. Its touch-sensitive screen includes a layer of capacitive material, just like many other touch-screens. However, the iPhone's capacitors are arranged according to a coordinate system. Its circuitry can sense changes at each point along the grid. In other words, every point on the grid generates its own signal when touched and relays that signal to the iPhone's processor. This allows the phone to determine the location and movement of simultaneous touches in multiple locations. Because of its reliance on this capacitive material, the iPhone works only if you touch it with your fingertip -- it won't work if you use a stylus or wear non-conductive gloves.
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and electrodes to determine where a user is touching. |
The iPhone's screen detects touch through one of two methods: Mutual capacitance or self capacitance. In mutual capacitance, the capacitive circuitry requires two distinct layers of material. One houses driving lines, which carry current, and other houses sensing lines, which detect the current at nodes. Self capacitance uses one layer of individual electrodes connected with capacitance-sensing circuitry.
Both of these possible setups send touch data as electrical impulses. In the next section, we'll take a look at exactly what happens.
Interpreting Touch-location Data
The iPhone's processor and software are central to correctly interpreting input from the touch-screen. The capacitive material sends raw touch-location data to the iPhone's processor. The processor uses software located in the iPhone's memory to interpret the raw data as commands and gestures. Here's what happens:
- Signals travel from the touch screen to the processor as electrical impulses.
- The processor uses software to analyze the data and determine the features of each touch. This includes size, shape and location of the affected area on the screen. If necessary, the processor arranges touches with similar features into groups. If you move your finger, the processor calculates the difference between the starting point and ending point of your touch.
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- The processor uses its gesture-interpretation software to determine which gesture you made. It combines your physical movement with information about which application you were using and what the application was doing when you touched the screen.
- The processor relays your instructions to the program in use. If necessary, it also sends commands to the iPhone's screen and other hardware. If the raw data doesn't match any applicable gestures or commands, the iPhone disregards it as an extraneous touch.
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All these steps happen in an instant -- you see changes in the
screen based on your input almost instantly. This process allows
you to access and use all of the iPhone's applications with your
fingers. We'll look at these programs and the iPhone's other
features in more detail in the next section, as well as how the
iPhone's cost measures up to its abilities.
iPhone Features and Applications
The front surface of the Apple iPhone has only one button -- the Home button. Pressing the Home button takes you to the main screen of the iPhone's graphical user interface. There, you can choose from the device's four primary functions using icons at the bottom of the phone:
- Phone: GSM or EDGE cellular phone service as well as a visual voice mail menu
- Mail: POP and IMAP e-mail access, including in-line pictures, HTML capabilities and push e-mail from Yahoo mail
- Web: Safari Web browser
- iPod: Music and videos
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Photo courtesy Apple |
The shape of the screen changes when you need it to as well -- you can shift the perspective from vertical to horizontal by tilting the phone. An accelerometer inside the iPhone lets the operating system know to change the orientation of the image on the screen. This means that you can scroll through long lists of music files on a long, narrow screen, and you can watch movies in a widescreen format. You can learn more about accelerometers in How the Nike + iPod Works and How the Nintendo Wii Works.
These features sound impressive, but many of them already exist on other smartphones. We'll explore the iPhone's competition and its pros and cons in the next section.
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