i got a problem, and time is running out for me, so please help me.

[itsmejohnny]

Hello,
i got a problem, and time is running out for me, so please help me.
On a form i got 2 fields. named field 1, field2, field3
They are attached to 1 tabel.

In field 1, is placed a value out a other tabel and got a value, say 20
Field 2 has a formula say field1*2, so the value is 20*2=40
In field 3 must come the value 40, without typing it, and automatic placed in the tabel assigned to field3

I don't know how to do this, please help
Reg,

John Netherlands

 

[rbooker]

In each field involved in the calculation, place the formula in the changeValue event.

Be sure and execute a "doDefault" before the formula so the formula uses the new value in the field.

 

[footpad]

John,

While Paradox supports calculated fields, the results are generated on the fly, e.g as you select new record, modify field values, and so on.

As rbooker points out, you need to add some code to your form to save the result of the calculated field into your table when it updates.

However, due to the way the event model works, it's a two step process: Detect the change and then save it to the table.

There are a number of ways to approach it (as well as a number of issues to work with). Here's a very simple demonstration:

1. Change your working directory to the one containing the samples provided with Paradox, e.g. the one containing LINEITEM.DB.

2. Create a new form and place LINEITEM in the data model. Accept all defaults.

3. Add a field to the form and define it as a calculated field with the following calculation:

[LINEITEM.Qty] * [LINEITEM.Selling Price]

Consider changing the label to something like "Calculation" to keep things straight visually.

4. In the newvalue event of your calculated field, add the following code:

   if Total.locked then
      self.postAction( userAction )
   endif

5. In the action event of your calculated field, add this code:

var
   numTotal  Number
endVar

   if eventInfo.id() = userAction then
      numTotal = Qty.Value * Selling_Price.Value
      if numTotal <> Total.Value then
         Total.Value = numTotal
      endIf
   endIf

6. Save and run your form.

If you change the selling price or the quantity of an item, the total will update. Note that you have to move off the field for the value to update.

Now, you need to be careful when you do this. It's very easy to wreak havoc with the event model. This example avoids that in two ways:

1. The update code is not triggered unless the record is actually locked, e.g. the Locked property of the Total field is TRUE.

2. The update process is not executed until after the events that triggered it (e.g. your movement) has processed. This is done with postAction(), which tells Paradox to trigger an event after it's done doing whatever it thinks it needs to.

Having said all that, this isn't the most efficient way to implement this. A better approach is to design your form so there is a record object containing the Total field. Put another way, you should be using a table frame or a multi-record object (MRO).

As you might expect, the Record object lets you control the way Paradox reponds to record oriented events, such as saving changes to disk and so on.

Once you've got a record object to work with, you'll want to rework this to:

a) Always trigger a dataPostRecord when Paradox attempts to save changes

b) Update the underlying Total field when changes to the record are saved.

You can do both by adding code to the record object's action event:

var
   siAction  smallInt
   numTotal  number
endVar

   siAction = eventInfo.id()
   switch
      case siAction = dataUnlockRecord : 
         self.action( dataPostRecord )
      case siAction = dataPostRecord : 
         doDefault
         numTotal = Qty.Value * Selling_Price.Value
         if numTotal <> Total.Value then
            Total.Value = numTotal
         endIf
   endSwitch

You can use this approach instead of the earlier one, however, the totals will only update when the record is saved. Most users prefer to see the total update on the fly.

If you simple can't use a Table Frame or an MRO, you can also do this on the Form's action() event, but it gets more complicated because you have to determine the table that generated the unlock request.

Generally, it's best to always use a Table Frame or MRO whenever possible.

As I said, it's simple request with a lot of considerations.

Hope this helps...

-- Lance

P.S. The code is off the top of my head, so there might be a typo or two. Apologies in advance.