PENDAHULUAN Object Oriented Programming * * * * Object Oriented Programming Konsep awal programming (Basic) dengan kekuatan GOTO statement Bahasa pemrograman terstruktur (procedural Language), menghilangkan kelemahan GOTO konsep programming tidak terstruktur Contoh: Pascal, Basic, FORTRAN, COBOL, C++, dll Object Oriented Programming, yang mengarah ke konsep object - Diperkenalkan pertama kali.
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Tutorial: Creating A FoxPro Multi-User Application
Dr. Thomas E. Hicks
Computer Science Department
Trinity University
For purposes of this tutorial, we shall start with the single user application created in the following tutorial.
Tutorial : FoxPro Create Application
1] Our RestaruantApp still resides in folder C:TempRestaurantApp. (See Below!)
2] The Project may be seen below:
1] By default the Use command opens the database in exclusive mode. A second user may not open either the database or the table. Note the exclusive on the status bar. See Below!
Open Database Rest
Use DataRest Order Name
Use DataRest Order Name
1] Let us now attempt to open database Rest and table Rest simultaneously on two foxpro appplications. These applications my be on two different computers; they may also be on the same computer as illustrated below.
Open Database Rest Shared
Use DataRest Shared Order Name
Use DataRest Shared Order Name
2] No longer does it say exclusive at the bottom of the status bar. The active record on both applications is record 1 of 54. Any function or form that enables the user to alter a record automatically lock the record as soon as a change is initiated. Edit and Change are two such functions. In the screen capture below, The top user is going to and a 2 is added to the end of the restaurant name; you can see Record Locked in the status bar as soon as the change is initiated. Once a user locks the record while making a change, it shall stay locked until the user moves to the next record.(See Below!)
3] Fortunately, locking the record does not prevent the other users from searching,running reports, running labels, examining data, or selection type queries. As you can see below, the bottom user can attempt to edit the same record and shall be successful until he/she attempts to make a change. (See Below!)
4] When the bottom user attempts to add a 2 to the end of the city Odessa, he/she gets a message Attempting To Lock ... Press Esc To Cancel. As soon as the top exits or moves on to another record, the bottom user will get a lock and be able to make his/her change. Really 'klugy' at this stage. (See Below!)
5] In the screen capture below, the top user finished editing record 1 and closed the edit window; the bottom user received a lock on record 1 and is able to make his/her change to Odessa. (See Below!)
6] Forms only compound these problems!
1] There are two basic modes.
- The Edit Mode shall lock the current database record and permit changes to that record.
- Options within this mode shall be only Cancel & Save
- The Normal Mode shall enable the user to
- Options within this mode shall be all else > Next, Previous, Top, Bottom, Search, Print, Browse, Edit, Add, Delete, Exit, etc.
2] For educational purposes, let us add two temporary buttons to our Rest form. (See Below!)
- The valid event for the Edit Mode button should be
Do SetEditMode - The valid event for the Normal Mode button should be
Do SetNormalMode
1] It is customary to work with a copy of the data in the edit mode; this greatly facilitates the ease of canceling the process with no damage to the original data. Some databases, such as FoxPro, have the option to easily create a set of local variables which contain a copy of the information in the current record; this function is called Scatter in the x-base languages.
In other database applications, such as Access, the programmer has to manually create and assign the needed local variables.
2] As you already know, Display Memory, will display all of the local variables -- followed by all of the system variables, etc. In the screen capture below, you can see that local variable NewName was assigned the value Dr.Thomas E. Hicks; Display memory shows this immediately before all of the system variable. (See Below!)
3] The current record is record 1 of 54. The Customer record has 9 fields; the notes field is a memo field. Scatter Memvar Memo creates 9 new local variables whose names are the same as those in the current record and whose values match those of the current record. Scatter Memvar makes a copy of all fields except memo fields. (See Below!)
3] The database field Name takes precedence over the local memory variable Name; therefore, ? Name will display the contents of the field variable Name and ? M.Name will display the contents of the local memory variable Name.
In the screen capture below, both Name and M.Name contain Abstruse Steak House2 because of the scatter. Name = 'Joes' will change local memory variable M.Name to 'Joes'. Replace Name With 'Mikes' will change the field Name of the current record to 'Mikes'. See Below!
1] A good application must enable the user to enter the edit mode, make some changes, and then discard those changes > thus returning to the original state. Change the control source of each of the variables on the Rest form. This means changing the control source of the Name1 field from Rest.Name to M.Name. Do likewise for all 9 fields; don't forget the Credit Card and Reservations!
2] Program Main must Scatter Memvar Memo prior to launching the form! The first part of main might be:
1] If you now run the main program, you will be disappointed that the Next, Previous, Top, and Bottom buttons will definitely not work; try them!
2] From this time forth, it will be necessary to scatter a copy of the memory variables each and every time you move the read/write pointer. Among the procedures that you will have to alter will be Next, Previous, Top, & Bottom. The scatter should occur after the pointer is moved and before the form is refreshed.
3] Functions such as GoTo, Seek, and Skip are among the items that move the record pointer. I leave it to you to decide exactly which functions need to be changed. The scatter is included in our new and improved Next procedure below. Take time now to scatter where-ever you need in the Code.prg.
4] Run the main program and make sure that your Add, Delete, Next, Previous, Top, Bottom, Delete, and Browse functions still work properly!
1] In the Normal mode, it is essential that each of the data fields must be read-only. We do not want the user moving the mouse into the data fields and making changes unless we are in the Edit mode. The following code will show you how to make the Name field read-only.
2] Do likewise for the other 8 fields in the Restaurant form. Procedure NormalMode should have 9 such assignments.
1] In the Edit mode, it is essential that each of the data fields must not be read-only; it is there that we shall permit the user to edit the data. It is there that we allow the user to move the mouse into the data fields and making changes. The following code will show you how to make the Name copy of the data accessible/not read-only.
2] Do likewise for the other 8 fields in the Restaurant form. Procedure EditMode should have 9 such assignments.
1] Run the form from your main program. Using the mouse, select/push the Normal Mode button. (See Below!)
2] All of the fields should be read only. Move the cursor into the City field. Try to make a change. If you are able to add something to the end of Kailua, you do not have the field read-only. Try all nine of the data fields. (See Below!)
3] Using the mouse, select/push the Edit Mode button. (See Below!)
4] All of the fields should not be read only. Move the cursor into the City field. Try to make a change. If you are unable to make changes something is wrong.I have added ntoto the end of Kailua below. Try all nine of the data fields to make sure that you can change each. (See Below!)
5] At the moment, the form is changing a memory copy of the data record. If you hit the Next and Previous buttons, you will find that the original record has not yet been changed; we will get to that in due time.
1] Once a user enters the Edit Mode, the record will soon be locked; others will not have access to this record. In order to reduce the complexity and encourage the user to quickly exit the Edit Mode, thus freeing the record for others. The Edit Mode shall disable all buttons except the Save and Cancel buttons.
2] The buttons on our form are graphic; we have a disabled picture image and a regular picture image associated with each. You need not associate images with regular buttons.
3] The Edit Mode shall Enable the Save and Cancel Buttons; it shall disable all other buttons. Do not disable the the Normal Mode and Edit Mode buttons; these are here for learning purposes and shall soon be deleted.
Enabled > Disabled >
4] Don't test yet!
1] Within the Normal Mode, the user shall have access to all buttons except the Save and Cancel.
4] Don't test yet!
1] Run the form from your main program. Using the mouse, select/push the Edit Mode button Note that all of the permanent form buttons, except Save & Cancel are disabled. (See Below!)
2] Using the mouse, select/push the Normal Mode button Note that only the permanent form buttons Save & Cancel are disabled. (See Below!)
3] The form should be initiated in the normal mode. Once the form is launched, the main program should evoke the NormalMode procedure. (See Below!)
1] The Add Procedure shall
- Scatter a temporary blank copy of the variables
- Enter the Edit Mode
- Refresh the form
- Move cursor to first field
- Allow the user to complete the information for the new record
2] Remember to add global variable__AddMode to your main program; initialize it to false.
Public __AddMode
__AddMode = .F.
3] The form should look like the following once the Add button is selected/pushed.
