In V2R3, a set of bindable OS/400 APIs called Dynamic Screen Manager (DSM) APIs became available, giving programmers a higher-level interface to the previously tedious method of 5250 data stream programming. Like 5250 data stream programming, DSM APIs provide the ability to dynamically read and write screens without the use of DDS display files or User Interface Manager (UIM) panel groups. The main advantage of this type of programming is that it allows you to dynamically build screens at run time rather than statically build screens at design time. However, because these APIs are bindable, they can only be used by ILE languages.

In V2R3, the only language that could be used with the DSM APIs was ILE C/400. In V3R1, with the release of RPG IV (which operates in the ILE environment), these APIs became accessible to RPG programmers. To demonstrate how these APIs can be used in an RPG program, I wrote the example shown in 6. The purpose of this program is to display the message "Hello World!" in the center of the screen. While it's not a particularly useful program, it does provide you with a starting point to build your own programs using these APIs.

In V2R3, the only language that could be used with the DSM APIs was ILE C/400. In V3R1, with the release of RPG IV (which operates in the ILE environment), these APIs became accessible to RPG programmers. To demonstrate how these APIs can be used in an RPG program, I wrote the example shown in Figure 6. The purpose of this program is to display the message "Hello World!" in the center of the screen. While it's not a particularly useful program, it does provide you with a starting point to build your own programs using these APIs.

To give you a better understanding of how this program works, I'll briefly explain the purpose of the various API calls. The program starts by calling the Create Command Buffer (QsnCrtCmdBuf) API. A command buffer is simply an area in memory where subsequent DSM API calls will place instructions until the API that "puts" the command buffer is called to execute those instructions. The Create Command Buffer API returns a handle that is used by the subsequent DSM API calls to locate the address of the buffer.

Next, the program calls the Clear Screen (QsnClrScr) API to place instructions into the command buffer that will clear the screen. The third call is to the Write Data (QsnWrtDta) API, which puts instructions into the command buffer to write data to the display. The data to display, as well as the row and column to display it at, are passed as parameters to this API. The next API call is to the Put Command Buffer (QsnPutBuf) API to execute the instructions that reside in the command buffer. At this point, the data is written to the screen. However, the program doesn't stop to wait for user input. Instead, it continues to execute. That's the reason for the last API call, which is to the Get AID (QsnGetAID) API. This API stops the program and waits for user input before continuing.

That's a quick overview of a sample program that uses the DSM APIs. Many more DSM APIs are available for you to try writing this type of code yourself. You'll find them documented in OS/400 System API Reference V3R1 (SC41-3801, CD-ROM QBKAVD00).

- Robin Klima

TechTalk: Getting started with the ILE Dynamic Screen Manager APIs.

Figure 6: Sample Program Using the DSM APIs

 *=============================================================== * To compile: * * CRTBNDRPG PGM(XXX/DSM001RG) SRCFILE(XXX/QRPGLESRC) + * DFTACTGRP(*NO) * *=============================================================== *. 1 ...+... 2 ...+... 3 ...+... 4 ...+... 5 ...+... 6 ...+... 7 D Size S 9B 0 INZ(4500) D Increment S 9B 0 INZ(50) D BufHandle S 9B 0 D Mode S 1A INZ('0') D Data S 12A INZ('Hello World!') D DataLength S 9B 0 INZ(12) D Row S 9B 0 INZ(13) D Column S 9B 0 INZ(35) * Create command buffer C CALLB 'QsnCrtCmdBuf' C PARM Size C PARM Increment C PARM *OMIT C PARM BufHandle C PARM *OMIT * Clear screen C CALLB 'QsnClrScr' C PARM Mode C PARM BufHandle C PARM *OMIT C PARM *OMIT * Write data C CALLB 'QsnWrtDta' C PARM Data C PARM DataLength C PARM *OMIT C PARM Row C PARM Column C PARM *OMIT C PARM *OMIT C PARM *OMIT C PARM *OMIT C PARM BufHandle C PARM *OMIT C PARM *OMIT * Put buffer C CALLB 'QsnPutBuf' C PARM BufHandle C PARM *OMIT C PARM *OMIT * Get AID key C CALLB 'QsnGetAID' C PARM *OMIT C PARM *OMIT C PARM *OMIT C EVAL *INLR = *ON