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About page navigation – PB Docs 105 – PowerBuilder Library

About page navigation – PB Docs 105

  2. Powerbuilder Documentation
  3. Powerbuilder Documentation Older
  4. Powerbuilder Documentation 10.5
  5. About page navigation – PB Docs 105

About page navigation

One of the
major tasks when creating a set of Web pages is managing how one
page links to another and how data is passed from one page to the next.

Navigation styles

You can link
from one page to another using any of three navigation styles:

  • A hyperlink using the HTML <A> element
  • A form submit for the page
  • A server redirection using self-navigation (where
    the form representing the current page submits back to itself)

All three styles let you bind parameters to target pages,
but the level of support for binding varies. Which navigation style
you choose depends on how you want data passed, whether or not the
data requires processing by the server, and the flexibility you
need. Most 4GL Web pages navigate to other pages by server redirection,
which provides the most flexible way to navigate from one page to
another. Server redirection can also be used to navigate from non-4GL
pages, but more coding is required. Table 10-1 next shows the advantages and disadvantages
of the three navigation styles.

Table 10-1: Navigation style advantages and
disadvantages
Navigation Advantages Disadvantages
Hyperlink
  • Jumps directly
    to another page without server processing
  • Works well with a range of different target pages
    when processing is unnecessary before moving to the target page
  • Allows non-matching names for parameter binding
    (binding defined in HREF attribute in page source)
  • Requires the values
    of parameters to be available when the page is generated.
  • Does not return to the server to process current
    page before moving to the next page. (Not all parameters and variables
    are available to the target page.)
  • Does not support server actions.
  • Does not support validation before navigation.
  • Does not allow the user to recover from errors caused
    by entering data in an invalid format.
Form submit
  • Jumps directly
    to another page without server processing
  • Requires the target
    page to define parameter names to match the parameters passed.
  • Provides only the data from the fields on the page
    form.
  • Does not support validation before navigation.
Server redirect
  • Supports validation
    and server actions
  • Processes the values of parameters before passing them
    to a target page
  • Allows non-matching names for parameter binding
    (binding defined in server script)
  • Retains the values of parameters and makes all the
    data available for parameter binding
  • Lets you redirect the client to another page from
    the middle of a server script
  • Lets you stop navigation if validation fails
  • Loads a current
    page, then the target page in the user’s browser (making
    this method slower than the other two styles).
  • Does not allow you to add FORM elements to a 4GL
    Web page. (A FORM represents an entire 4GL Web page.) You can still
    insert form field controls, but they are not surrounded by FORM
    tags in Source view.

Target pages

When
you develop Web pages, you can specify a target page that already
exists, or one that you plan to create. If you specify a page that
already exists, you can bind values from the linking page to the
parameters of the target page. If you specify a page that does not
yet exist, you can set parameters on the linking page; then, when
you create the target page, you specify which parameters it requires
of those being passed from the linking page. For more information about
page parameters, see “Setting up page parameters”.

Parameter binding

When you establish
navigation from one page to another, you can bind values from the
linking page to parameters on the target page. 4GL Web pages support several
types of parameter bindings:

Table 10-2: Parameter binding for 4GL Web pages
Type of binding Description Navigation style restrictions
Constant A fixed value Not available for form submit.
Page Variable A variable whose value is set on the server Only initial value used by hyperlink (cannot
be changed by client). Variable name must match parameter name on target
page for form submit.
Page Parameter A parameter whose value is set on the
server		 Only initial value used by hyperlink (cannot
be changed by client). Parameter name must match parameter name
on target page for form submit.
Expression The value of an expression set on the
server		 Not available for form submit.
Control The value property of a server object Not available for hyperlink.

The user interface for binding parameters is different for
each navigation style:

Table 10-3: Information about navigation style and parameter binding
Navigation style For information, see
Hyperlink “Managing client hyperlinks”
Form submit “Managing client form submission”
Server redirect “Managing server redirection”
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August 3, 2023
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