Webmaster''''s Guide to the Wireless Internet part 30 pps

Table 6.6 Attributes of the Tag Href Refers to the location of the Text document being linked to, identical to desktop browser Name Refers to the anchor itself, Text identical to deskto

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Using the <a> Tag

The anchor tag is the defining feature of HTML versus other document tech-nologies, and arguably the most important tag in any Webmaster’s repertoire.The

anchor tag supports three different attributes within Clipper: href, name, and

button.The meaning and syntax of these attributes is described in Table 6.6.

Table 6.6 Attributes of the <a> Tag

Href Refers to the location of the <a href=””>Text</a>

document being linked to, identical to desktop browser Name Refers to the anchor itself, <a name=””>Text</a>

identical to desktop browser Button Displays link as button, unique <a href=”” button>Text</a>

to Clipper

The LocalIcon Meta Tag

It is possible to include extra images within a WCA by specifying them

as a LocalIcon by using the following syntax:

Doing so will instruct the WCA Builder to bundle the image within your pqa, thus ensuring that the icon exists on the local device (we rec-ommend including all of these references in the index page of your application to keep track of them) You can reference these images later

in your server responses with the following syntax:

Clipper will find the image on the local device and display it to the user without them having to download the image from your Web site and send it over the air to the device This is the preferred method of using images in a server response It will require some forethought when you initially build your WCA, but it will help to create a faster (and cheaper) user experience!

Developing & Deploying…

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The protocols shown in Table 6.7 are valid with an anchor tag in a Web clip-ping sent to a browser or WCA installed on the device.

Table 6.7Protocols Valid with the <a> Tag

Protocol Resource

http:// Uniform Resource Identifier (URI) accessed via HTTP

https:// Uniform Resource Identifier (URI) accessed via secure HTTP

mailto: E-mail address, accessed via the Exchange Manager The

Exchange Manager calls the default e-mail application This is accomplished via Messaging Application Programming

Interface (MAPI), which is the same library that handles this action on a desktop computer

file: Location of file on device You can access individual pages with

an installed WCA by using the following syntax:

palm: Application on device When linked to, Clipper is closed and

the requested location is launched in place of Clipper For example, <a href=”palm:memo.appl”> can be used to launch the Memo Pad

palmcall: Application on device When linked to, the application is

launched from Clipper, and Clipper remains in the background until the application is closed

Whenever Clipper has to send information over the air, it will render three small lines to the left of a link, whether it is a text link or a button.This over-the-air icon informs users that they will be sending and receiving data over the wireless network, and will correspondingly incur charges Links that point to a page that is located on the device using the protocols will not have this symbol A secure link will show the image of a small key and the over-the-air icon.

Using the <form> Tag

The <form> tag is a very important aspect of Web clipping, as it enables your WCA to send data to a Web server located on the Internet Clipper allows you to

use both GET and POST methods, and you must specify an action attribute, which

specifies a Uniform Resource Identifier (URI) for your form to send data to.

Using the <select> Tag

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within the <select>), and behaves almost exactly the same as it does in a desktop browser.The select element supports the attributes shown in Table 6.8.

Table 6.8Attributes of the <select> Tag

Name String Name of variable Required – N/A

containing selected value to be sent

to server Size Number Number of options to 1

be displayed Multiple Minimized attribute, Allows multiple options Off

no value needed to be selected; in order

to enable a scrollable list, the minimum value is 2

Using the <input> Tag

The <input> element allows the user to input information that can be sent to a

server for processing It supports a wide variety of formats via the type attribute.

The <input> element supports the attributes shown in Table 6.9.

Table 6.9Attributes of the <input> Tag

Attribute Meaning

Type The type of input to be rendered: valid values for this include

text, password, hidden, radio, checkbox, submit, reset Name Name of variable containing value to be sent to server

Value Predefined value

Checked Specifies that an input with type radio or checkbox will be

checked Size Specifies the length, in character units, of the input (of type

text) to be rendered

Maxlength Specifies the maximum number of characters that may be

entered in an input of type text

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There are also two Palm OS-specific values that may be specified for the input element: timepicker and datepicker See the section, “Web Clipping Extensions.”

The <input> element behaves quite similarly to its standard HTML counter-part, with the exception of the radio button (type=radio).This type is rendered as

a box, which may be selected by the user In order for this box to display any text, the label must be inserted directly after the input tag, as shown in Figure 6.19 and Figure 6.20.

Figure 6.19Adding Radio Buttons

<html>

<head>

<title>Radio Button</title>

</head>

<body>

<h1>Radio Button Example</h1>

<input type="radio" name="radio" value="Option1">Option1<br>

<input type="radio" name="radio" value="Option2" checked>Option2<br>

</form>

</body>

</html>

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Web Clipping Extensions

There are a few elements unique to Web clipping.These include some <meta> tags that relay information to the Proxy Server, variables that can be used to identify unique devices and their approximate locations, and objects that can gather date and time data from the user.

NOTE

If you have HTML on your existing site that you would like to make avail-able to Web clipping users, you can mark it with the <smallsscreenig-nore> tag, which tells the proxy server to ignore the code in between

Palm-Specific <meta> Tags

There are many <meta> tags and header information that are specific only to Web clipping A full list of these tags is described in Palm Inc.’s Web Clipping Developer’s Guide, located at www.palmos.com/dev/tech/docs/webclippings/ PalmWebClippingFront.html.Table 6.10 describes the most common and useful tags that you can use to relay information.

Figure 6.20Radio Buttons Added in Clipper

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Useful Meta T

Specifies text to be displayed when users view their his- tory

Clipper will display the time the clipping was viewed

of an image to be included in a WCA and stored on the device

Specifies that a clipping is safe for Clipper and that it should not be modi- fied by the P

strongly encouraged that you include this tag in all of your server responses

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Palm OS 4.0 offers a great many more <meta> tags than those listed here, including some caching mechanisms As time progresses, you may be interested in implementing some of the newer features of Web clipping

Identifying Users with a Device ID

There is a special variable that you can access on any device that supports Web clipping It is referenced as such:

This variable is returned in the format [1, 0, -1].[X].

The content of the first brackets corresponds to the type of device:

■ A value of 1 is returned if the proxy server recognizes the device ID as being a Palm VII.

■ A value of 0 is returned if the device cannot be determined to be a Palm VII or other device.

■ A value of –1 is returned if the proxy server can determine that the

device is not a Palm VII.

The content of the second set of brackets is a unique string that is created upon device activation.You can use %DEVICEID to identify unique users, but with limited reliability Depending on the network from which your user is accessing your application (Smart Phones in particular), the value of %DEVICEID may change from session to session, and, in some cases, within a particular session.

NOTE

The actual string format of %DEVICEID may change as time progresses,

so it should be treated as a black box when used in a server-side applica-tion That is, do not make any assumptions as to the exact format of the string Be sure to accommodate this in your application in order to create the best experience for your users

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SECURITY ALERT

You should not associate any personal information with %DEVICEID

Mobile devices are susceptible to theft, and sensitive information may be compromised if %DEVICEID is the only method of authentication

Furthermore, a determined user can obtain the %DEVICEID from other devices by offering a Trojan Horse PQA There is not a reliable means of

Using %DEVICEID to Recognize Individual Users

Given that a Palm.net proxy server processes all Web clipping transac-tions, you cannot use the user’s IP address to identify individual users because all requests will be written to your server logs with the IP of the proxy server Also, cookies are supported only for Palm OS 4.0, which, at the time of this writing, is not yet prevalent in the market The %DEVI-CEID element was implemented as a cookie substitute and was intended

to allow developers to identify individual devices

There are, as previously mentioned, issues with the implementation that severely limit the usage of %DEVICEID for authentication in an envi-ronment that deals with sensitive data However, if no real damage will

be caused if the %DEVICEID of a particular user is spoofed, and you make sure to rely only on %DEVICEID for Palm VII users (since it may change midsession for users of other networks), you can use it reliably

to identify individual users in a variety of situations

For example, if you offer downloadable stock quotes, you may pro-vide your users with an option to customize their preferences and select the stocks they want to see You can develop your application so that when the user initiates a request for stock quotes from their device, they receive quotes for the stocks in which they are interested This is an effective means of providing a positive user experience while minimizing data sent over the air

The %DEVICEID element provides Webmasters with something we previously have had to generate ourselves, namely, a unique key that represents an individual user (device) This identifier is unfortunately insecure and not always reliable (depending on the user’s connection network), so you must take care in how you use it

Developing & Deploying…

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Estimating User Location by ZIP Code

The %ZIPCODE variable contains the ZIP code of the nearest Web clipping base station to the user.This will provide a rough estimate of where your user is located at the time of access, accurate to within approximately 10 miles.

NOTE

This variable may not be always available Unless your user is connected via the Mobitex network, you will not be able to utilize this feature of Web clipping In the event that the ZIP code is unavailable, %ZIPCODE returns a value of 000000 You can work around this by building some detection into your server-side application that allows users to enter their locations as opposed to submitting the %ZIPCODE value automatically Palm OS 4.0 offers much more information about the user’s network, including information regarding the latitude and longitude of the loca-tion, as well as county, city, state, and country information If you are in

a situation in which you can reliably know what type of hardware your users have (such as a corporate environment), then you may be able to take advantage of this information before the 4.0 OS becomes prevalent

in the general market

Selecting a Date with the Datepicker Object

A very useful element unique to the Web clipping environment is the datepicker object.You can invoke the datepicker object to generate a string containing a date:

NOTE

The date attribute is output in YYYY-MM-DD format, but dates are assigned using the MM/DD/YYYY format shown in the preceding code

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If you omit the value attribute, or if the value is not in the expected format, then the current date will be displayed Figure 6.21 shows how the datepicker object looks in the POSE (in this case, we have specified 01/01/2001 as the date within the HTML code).

When users click on the input field, they are presented with a clickable cal-endar that allows them to select a date (see Figure 6.22).

The user is also given the option to select Today as the date.This option allows the user to select the current date Upon pressing the Today button, the

user is returned to the page containing the datepicker object, as illustrated in Figure 6.23.

Figure 6.21Datepicker Object with Value Attribute Omitted

Figure 6.22Selecting a Date

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