As I've studied OOP a little more recently, I hear of this matter of depency injection. Can someone help explain this to me, from a VFP perspective.

I think my question here may be associated to it... On my form class, I have a method that will calculate the total amount of the invoice, by summing the line item costs based on the parent key.

So, I have a method on the form called CalculateLineItemCost().

Now, I could architect this thing where the method assumes the current parent key from a form property which is (kept updated by the navigation of the form), or I could architect it to where the parent key value has to be passed into the method by the calling method.

pseudo code of each example to follow:

Assume parent key from a form property:

Method CalculateLineItemCost()

 liParentKey=thisform.iParentKey
 select sum(qty*cost) from LineItems where ifkey=liParentKey into array laTotalValue
 return laTotalValue

EndMethod

or, I could require the parent key value to be passed in, like this:

Method CalculateLineItemCost()
lparameters tiParentKey

 select sum(qty*cost) from LineItems where ifkey=tiParentKey into array laTotalValue
 return laTotalValue

EndMethod

So, which way is considered the best practice?