1、g when entering/leaving cells. In fact, several bugs are known by Sheridan, yet they insist that the workarounds (timely refreshes) will cover up the bugs. For the most part its true, but not without great effort and debugging. For very simple applications, the controls seem to work adequately. Usin
2、g bound drop-down combo boxes (with automatic list searching by typing the starting letters of the list element) can be implemented as separate controls or within a grid with relative ease.Q+E Multi Link by Intersolv - Q+E Multi-Link are marketed to serve the needs of those developers who wish to si
3、mplify data access to a number of popular databases. This product consists of several custom controls with built-in QBE for storing queries. Database access uses Intersolv drivers (versus ODBC) which are generally more efficient than the native ODBC drivers. Other custom controls simplify the proces
4、s of navigating through result sets, retrieving/writing to record sets, and displaying data. There have been documented problems in this product with accessing Sybase System 10 databases.VSVBX by VideoSoft - VSVBX is a very powerful, yet relatively inexpensive product. This VBX is highly recommended
5、 for its ability to resize forms/controls at run-time using what VideoSoft calls Elastics. These elastics are similar to 3-D frames for grouping of related controls on a form, however an elastic can readily be configured to proportionally resize the controls on a form whenever the user resizes the w
6、indow. Elastics can be used to position itself and its controls along any of the edges of a window (i.e. a constant -sized status bar at the base of the window). VSVBX also provides VB with a tab system that works quite well.SpreadVBXFormula OneTechnical ArchitectureFile Versions - Before beginning
7、development, identify all the essential .DLLs, .DRVs, and .VBXs that will be used on the project. After identifying these files, make sure that you have the correct version (not always the most recent) of the files. File Locations - Once identified, these files should then be centrally located on th
8、e server (or floppy disk if no server is available). Any updates should be added to development documentation and to the central storage location so that all developers can update their PCs. This might seem like a big hassle at first, but it will pay off in the long run (especially when you go to cr
9、eate the executable and setup the client workstations). Memory Allocation Tools - A tool that will help you define which files are loaded into memory by your application is Microsoft Windows Process Status (WPS.EXE). This executable ships with VB and is stored in the VBCDK directory. When using WPS
10、to identify files used by your VB application, close all applications (including Clock or Norton Anti-Virus), start WPS, and select the File/Save Dump option in order to output this information to a text file. The compiled VB application should then be started, and the new WPS information (click Upd
11、ate to be sure that the list has been refreshed) should be saved to a text file. Comparing the two lists will then show the additional files loaded by the VB application, and therefore are required on the distribution disk.Extraneous Files - All extra .VBX and .DLL files that will not be used by you
12、r application should be removed from the VB project. Advantages of doing this include:Reduces system resources required during developmentDecreases size of the application executableMakes it easier to recognize which control is which on the toolboxReport Writer Version - Although VB ships with Cryst
13、al Reports 2.0, it integrates with the 4.0 release of the report writer. Even though the Crystal Reports 4.0 user interface is still not as friendly as Access 2.0, it may be worth purchasing. The main benefit in this version is that it allows the developer to replicate the database structure on a lo
14、cal PC. This allows a developer to create reports at home without connecting to a live database. (Note: The Access 95 will allow VB 4.0 to use the report writing feature using OLE 2.0 technology.)Report Writer VBX - When using Crystal Reports, be sure to have to most updated version of the CRYSTAL.V
15、BX file. For version 2.0, you need to have the file dated 10/1/93 or newer. For version 4.0, use the VBX that ships with the software.Image Objects - Using the Image object instead of the PictureBox object to add graphics to an application will greatly enhance the display speed of forms. The Image o
16、bject does not offer as many property settings as the PictureBox object, and therefore is not as customizable, but for simple graphic display, it is the recommended tool.Application .INI Files - The .INI file for the executable should be placed in the users WINDOWS directory and have the same name a
17、s the executable file but with the .INI extension (e.g., MYPROG.EXE should have MYPROG.INI in the WINDOWS directory). Although the VB manual and support team offers several scenarios, this one has always worked.Updating .INI Files - Any changes made in the VB.INI file that affect database access or
18、reporting should also be made the application .INI file.Database ConnectivityAccess Jet Engine and Compatibility LayerWhat is the Capability Layer - The Visual Basic Capability Layer (VBCL) upgrades the VB 3.0 database access engine (“Jet”) from compatibility with MS Access version 1.1 to the curren
19、t release of 2.0. There is also an upgrade for the Jet engine for 2.0 (MSVC - upgrade to MS Access 2.5) which has much better performance from within VB. The following is a list of additional functionality that MSAccess 2.0 provides over version 1.1:ANSI SQL-89 Level 1 compliance - not such a big de
20、al, considering many databases are SQL-92/93 compliant. However, you can use DDL (data definition language) to create and alter tables.Validation rules for the data reside at the engine level (i.e. Field properties section of each table).Cascading updates and deletes.Union queries and subqueries, TO
21、P N queries. Access 1.1 Jet Engine - If your client has a VB application, and decides to upgrade Microsoft Access from 1.1 to 2.0, then make sure that they do not remove the Access 1.1 Jet Engine. This will prevent existing VB applications from performing correctly.Query Patching Program - When usin
22、g MS Access as the database, it is often useful to create a simple VB application that will add/modify/delete defined queries in your database (i.e. a query patching program). This will simplify the maintenance of the system, as the database will not have to be tied up each time there is a change to the databases queries.Using Btrieve (Network and Stand Alone)Btrieve Files - In order to attach to Btrieve using VB, the following files must exist in the WINDOWS/SYSTEM directory on the development/application wor
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