Screen class

Introduced in version 7.1 of the Sirius Mods, Screen objects are designed to make writing and maintaining User Language full-screen applications easier. They also let you take advantage of dynamic 3270 screen sizes in your applications.

Most modern 3270 emulators allow flexible definitions of 3270 screen sizes beyond the standard Models 2, 3, 4, and 5. Traditional User Language screen definitions define a fixed layout for a screen and so must be designed to be display correctly on even the smallest screen. This is usually the 3278 Model 2, which contains a none-too-generous 24 rows by 80 columns. Though a screen designed for a 24x80 layout will usually display correctly on other models, screens designed for other models may display misaligned data on a smaller screen, often rendering the application unusable on these screen types. This leaves the application programmer little choice but to design for the lowest common denominator -- Model 2 -- wasting precious screen space on larger screens.

With Screen objects, screen definition takes place during User Language request evaluation instead of during compilation, freeing the programmer to detect and take advantage of the current screen size and to make more efficient use of available screen space. It is therefore possible for a single application to support many different screen sizes without changing User Language code or resorting to special $functions to manipulate a traditional screen layout.

System space for Screen objects

Traditional User Language full-screen applications use FSCB (Full SCreen Buffer) space to hold 3270 screen definitions. Since screen objects are part of Janus SOAP, the design must fit within this existing object-oriented architecture, which cannot utilize FSCB space. As a result, screen objects use STBL space for dynamic screen definitions.

Because the entire screen image must be in contiguous storage, any instance of a screen object must allocate the maximum allowable STBL space, even if some of this space may not be used by a particular application. You use the SCRNSTBL user parameter, which specifies the maximum size per screen, to prevent unnecessary waste of STBL space and to limit an application to a reasonable amount of space to prevent STBL exhaustion.

A good starting value for SCRNSTBL is 6144 (this is the default as of Sirius Mods 7.3 and maintenance to earlier versions). Scrolling applications and applications designed for large screens with many fields may require two or more times this storage. An application that exceeds its screen STBL allocation is canceled.

The Screen class

The Screen class provides an object-oriented equivalent of the Model 204 full-screen feature. An instance of a Screen object is equivalent to a screen you might define with the User Language full-screen feature. The Screen methods specify layout and certain visual attributes of each screen: where screen items are to appear on the video display, and how they are to be highlighted or colored.

Screen objects are composed of screen fields and not screenlines as in the full-screen feature, and multiple screen fields may form the equivalent of a single screenline (or row). These screen fields are themselves objects: instances of the ScreenField class. In this documentat, ScreenField objects are sometimes referred to as “fields” and sometimes as “screenfields.”

Screen methods

The individual Screen methods are described in the following sections. For information about the conventions followed, see Conventions and terminology.

ActionKey property

This read-only property returns an actionKey enumeration which is the keyboard key that activated the last screen read. ActionKey enumerations are pf1 through pf24, and enter.

%key = %screen:actionKey

ActionKey syntax

Syntax Terms

%key A declared ActionKey enumeration. Valid values are Enter and pf1, pf2, and so on through pf24. The value that is set initially is Enter.

%screen A reference to an instance of a Screen object.

Usage Notes

You can use the ActionKey class ToNumber method to convert ActionKey enumeration values to a numeric value: the integer that remains after the key name is stripped of its “PF” prefix. For Enter, the numeric value is 0. These values are useful in a value-testing loop in conjunction with the User Language JUMP statement.

AddField function

This callable function adds a field (an instance of a ScreenField object) to the screen represented by the method object (an instance of a Screen object).

A ScreenField can only be defined within the limits of the current screen. The number of rows and columns in the current screen is determined by Screen class methods (“Rows property” and “Columns property”, below). An attempt to define a field outside these boundaries results in request cancellation. If any part of a new screen field would overlap an existing field, the request is cancelled.

[%sfield =] %screen:AddField( [Color=fieldcolor,] [Column=num,] [Highlight=bool,] [Invisible=bool,] [Itemid=num,] [Modified=bool,] [Numeric=bool,] [Protected=bool,] [Row=num,] [Value=string,] [Width=num,] )

AddField syntax

Syntax Terms

%sfield A declared ScreenField object that is set to a new ScreenField object reference.

%screen A reference to an instance of a Screen object.

Color= fieldcolor The optional Color argument (name required) is a Fieldcolor enumeration value. Valid values (case unimportant) are turquoise, green, blue, red, white, yellow, and pink. The default is blue.

This parameter explicitly sets the color for a screen field. The Color method (“Color property”, below) lets you reset it. You can use the ProtectedColor (“ProtectedColor property”) and UnprotectedColor (“UnprotectedColor property”) methods to set defaults for a screen's protected and unprotected fields, respectively.

Column= num The optional Column argument (name required) is a numeric value indicating the first column position in the field. This first column, in any field, is reserved for an attribute byte and cannot contain displayable data (it appears on a screen as a blank). The field's value (display data) begins by default in the column immediately following the reserved column. The first column in a screen is column 1; the last column can be determined with the Columns method (“Columns property”, below).

The default Column value is one greater than the ending column number of the preceding field, or it is 1.

Highlight= highlight The optional Highlight argument (name required) is a Highlight enumeration value. Valid values (case unimportant) are: Underline, Reverse, Blink, or None. A ScreenField may have only one Highlight attribute. The Highlight property (“Highlight” on page 909) lets you reset it. The default is None.

Invisible= bool The optional Invisible argument (name required) is a Boolean enumeration value: if True, any data in the field will not displayed on the terminal. If False (the default), the screen field data is displayed on the terminal. The Invisible property lets you reset the value. The invisible attribute can be applied to protected or nonprotected fields. It is typically used to hide password prompts or other private data, but it does not encrypt or suppress transmission of data over the network. It is intended to minimize theft of private data at terminals situated in non-private areas.

Itemid= num The optional Itemid argument (name required) is a numeric value assigned to the the screenfield that allows the CursorItemID method (“CursorItemID” on page 899) to identify the screenfield that contains the cursor after a screen read.

The default ID number is 0. The item ID should be a unique value for each screenfield, but this is not enforced by the AddField method. You can reset the ID using the ScreenField ItemID method (“Itemid property”, below). ItemIDs are most useful when using arraylists of ScreenFields. This is commonly done for scrolling applications.

Modified= bool The optional Modified argument (name required) is a Boolean enumeration value that indicates whether a ScreenField value has been modified by the user: True indicates the ScreenField has been modified by the user. The default, False, indicates the ScreenField has not been modified.

Regardless of the initial setting of this argument, the value of the Modified property (“Modified” on page 911) for a field is always set by the Read method.

Numeric= bool The optional Numeric argument (name required) is a Boolean enumeration value: if True, and the field is not protected, only numeric values may be entered in the field. Numeric values must be composed of the characters 0 through 9, plus (+), minus (-), and period (.). If False (the default), field input is not restricted to numeric data. The Numeric property (“Numeric”, below) lets you reset the value.

Regardless of the value of the Numeric attribute, the programmer can assign any type of value to the field. Enforcement of the Numeric attribute takes place only when a user enters data in the field. Some terminal emulators do not enforce numeric field restrictions, so the programmer should be aware that the value of a numeric field must still be checked for validity.

Protected= bool The optional Protected argument (name required) is a Boolean enumeration value: if True, the field will be protected against modification by the user when the screen is displayed. If False, the screen field will be an input field. New fields are protected by default. The value of this attribute can be reset using the Protected method (“Protected property”, below).

Row= num The optional Row argument (name required) is a numeric value indicating the starting row number for the field. The first row in a screen is row 1, and the last can be determined with the Rows method (“Rows property”, below). Any row number in the screen may be used for a field. No rows are reserved by Janus SOAP. A field may occupy more than one row.

The first position in any field is reserved for an attribute byte, which cannot contain displayable data and appears on a screen as a blank. A field's display data begins by default in the column immediately following the reserved byte.

The Row default value is 1 or the value specified or implied by the previous AddField call.

Value= string The optional Value argument (name required) is a string that contains the screen data to be displayed. The Value parameter is simply a convenient way to set display data when the screenfield is instantiated.

The ScreenField class Value method performs the same work, but can also get user-entered data for a screenField. For more information on setting and getting screenField values, see “Value property”, below.

Width= width The optional Width argument (name required) is a numeric value indicating the length of the screen field, excluding the attribute byte. The first position in any field is occupied by an attribute byte, which cannot contain user data. The minimum width for a field is 1, and the maximum width is 255. If no width is specified, the width of the field is determined by the length of the string specified in the method's Value parameter. If neither a Width nor a Value parameter is specified, the request is cancelled. If both Width and Value parameters are specified, the Width parameter is used to set the field width, and the Value is silently padded or truncated accordingly.

The Width property lets you reset the width.

Usage Notes

Each of the screenfield attributes specified by the AddField optional parameters can be updated by their like-named methods in the ScreenField class. The “modified” and “value” attributes are also set by a user screen-interaction.

References

The Janus SOAP manual in PDF format: http://sirius-software.com/maint/download/jansoapr.pdf