Advantage and drawbacks of Modify and Describe methods in PowerBuilder

In PowerBuilder, using the Describe and Modify methods to access DataWindow object property values has an advantage and some drawbacks. The examples here use Modify as illustrations, but similar considerations apply to Describe.

Advantage

Allows you to specify column and property names dynamically In your script, you can build a string that specifies the column and property names.

For example, the following code builds a string in which the default color value and the two color values in the If function are determined in the script. Notice how the single quotes around the expression are included in the first and last pieces of the string:

red_amount = Integer(sle_1.Text)

modstring = "emp_id.Color='" + &

		String(RGB(red_amount, 0, 0)) + &

		"~tIf(emp_status=~~'A~~'," + &

		String(RGB(255, 0, 0)) + &

		"," + &

		String(RGB(red_amount, 0, 0)) + &

		")'"

Modify(modstring)

The resulting string when red_amount is set to 128 is:

emp_id.Color='128~tIf(emp_status=~'A~',255,128)'

The following is a simpler example without the If function. You do not need quotes around the value if you are not specifying an expression. Here the String and RGB functions result in a constant value in the resulting modstring:

Modify(ls_columnname + ".Color=" + &

		String(RGB(red_amount, 255, 255)))

Drawbacks

Setting several properties at once is possible but hard to debug Although you can set several properties in a single method call, it is harder to understand and debug scripts that do so.

For example, assume the following is entered on a single line in the script editor:

rtn = dw_1.Modify("emp_id.Font.Italic=0

oval_1.Background.Mode=0

oval_1.Background.Color=255")

Less efficient than an expression Using a DWObject variable in several property expressions is a little more efficient than setting several properties in a single call to Describe or Modify. However, if you want to be able to name controls dynamically, you might still choose to use Describe or Modify.

For examples of using a DWObject variable, see “Using the DWObject variable in PowerBuilder”.

Can require complex quoted strings When you specify an expression for a property value, it is difficult to specify nested quotes correctly—the code is hard to understand and prone to error. For Describe, this is less of a drawback—strings do not become as complex because they do not include an expression.

For example, this string entered on a single line in a script assigns a DataWindow expression to the Color property:

Modify("emp_id.Color=~"16777215 ~t

If(emp_status=~~~"A~~~",255,16777215)~"")

For more information about quoted strings, see “Nested strings and special characters for DataWindow object properties”.