How a DataWindow control manages data – PB Docs 126

How a DataWindow control manages data

As users add or change data, the data is first handled as
text in an edit control. If the data is accepted, it is then stored
as an item in a buffer.

About the DataWindow buffers

A DataWindow uses three buffers to store data:

Table 2-1: DataWindow buffers

Buffer

Contents

Primary

Data that has not been deleted or filtered
out (that is, the rows that are viewable)

Filter

Data that was filtered out

Delete

Data that was deleted by the user or
through code

About the edit control

As the user moves around the DataWindow control, the DataWindow
places an edit control over the current cell (row and column):

udwo09.gif

About text

The contents of the edit control are called text. Text is
data that has not yet been accepted by the DataWindow control. Data
entered in the edit control is not in a DataWindow buffer yet; it
is simply text in the edit control.

About items

When the user changes the contents of the edit control and
presses Enter or leaves the cell (by tabbing, using the mouse, or
pressing up arrow or down arrow),
the DataWindow processes the data and either accepts or rejects
it, depending on whether it meets the requirements specified for
the column. If the data is accepted, the text is moved to the current
row and column in the DataWindow Primary buffer. The data in the
Primary buffer for a particular column is referred to as an item.

Events for changing text and items

When data is changed in the edit control, several events occur.
The names of the events are different in each environment, as shown
in the table. This chapter refers to events using PowerBuilder names.

Table 2-2: Event names in different environments

Event

Description

For PowerBuilder, Web DataWindow client
control

For Web ActiveX

EditChanged (not available on client control)

onEditChange

Occurs for each keystroke the user types
in the edit control

ItemChanged

beforeItemChange

Occurs when a cell has been modified
and loses focus

ItemError

onItemError

Occurs when new data fails the validation
rules for the column

ItemFocusChanged

onItemFocusChange

Occurs when the current item in the control
changes

How text is processed in the edit control

When the data in a column in a DataWindow has been changed
and the column loses focus (for example, because the user tabs to
the next column), the following sequence of events occurs:

  1. The DataWindow control converts
    the text into the correct datatype for the column. For example,
    if the user is in a numeric column, the DataWindow control converts
    the string that was entered into a number. If the data cannot be
    converted, the ItemError event is triggered.

  2. If the data converts successfully to the correct
    type, the DataWindow control applies any validation rule used by
    the column. If the data fails validation, the ItemError event is
    triggered.

  3. If the data passes validation, then the ItemChanged
    event is triggered. If you set an action/return code of
    1 in the ItemChanged event, the DataWindow control rejects the data
    and does not allow the focus to change. In this case, the ItemError
    event is triggered.

  4. If the ItemChanged event accepts the data, the ItemFocusChanged
    event is triggered next and the data is stored as an item in a buffer.

Figure 2-2: How text is processed in edit controls

udwo10d.gif

Action/return codes for events

You can affect the outcome of events by specifying numeric
values in the event’s program code. For example, step 3
above describes how you can force data to be rejected with a code
of 1 in the ItemChanged event.

To specify action/return codes:

  • PowerBuilder and Web DataWindow

    Use a RETURN statement

  • Web ActiveX

    Call the SetActionCode or setActionCode method

For information about codes for individual
events, see the DataWindow Reference.


Document get from Powerbuilder help
Thank you for watching.
Was this article helpful?
Subscribe
Notify of
guest
0 Comments
Inline Feedbacks
View all comments
0
Would love your thoughts, please comment.x
()
x