Hackers Guide to Visual FoxPro 7.0 - page 61
Cos(), Sin(), Tan(), ACos(), ASin(), ATan(), ATn2(), DToR(), RToD(), Pi()
Sines, sines,
everywhere there's sines,
breakin' up the
scenery
,
blowin' my mind
—with apologies to Five Man Electric Band
Okay, everyone remembers their high school trigonometry, right? No? We don't blame you. With any luck, you will never be called upon to write an app requiring these functions, but it's nice to know they're available should you need them.All the functions describe angle in terms of radians, a unit of measure. (You might remember there are 2 times pi radian units in a circle, just as 360 degrees describes the circle.) If you need to convert your angles back and forth between the two numbering systems, the DTOR() and RTOD() functions allow you to switch back and forth between the units of measure. All functions properly respect nulls, returning null if any of their supplied parameters are null.
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Usage
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nRetValue = COS( nAngle )
nRetValue = SIN( nAngle )
nRetValue = TAN( nAngle )
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Parameter
|
Value
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Meaning
|
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nAngle
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Numeric
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The angle to calculate,
expressed
in radians.
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nRetValue
|
Numeric
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The trigonometric value of the specified angle.
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These three functions—sine, cosine and tangent—return the equivalent trigonometric functions.
Example
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? COS(PI()/3) && returns 0.50
? SIN(PI()/3) && returns 0.87
? TAN(PI()/3) && returns 1.73
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Usage
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nRetValue = ACOS( nTrigValue )
nRetValue = ASIN( nTrigValue )
nRetValue = ATAN( nTrigValue )
nRetValue = ATN2( nXValue, nYValue )
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Parameter
|
Value
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Meaning
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nTrigValue
|
Numeric
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The value returned from the trigonometric function.
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nXValue, nYValue
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Numeric
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The X and Y coordinates of a point in any of the four quadrants describing a line through the origin. This line and the line y=0 form the angle returned by ATN2().
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nRetValue
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Numeric
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The angle, in radians, whose trigonometric value is supplied to the function.
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The "arc" functions (arcsine,
arccosine
and arctangent are inverse trigonometric functions) return what angle must have been supplied to their matching trigonometric functions (sine, cosine and tangent) to return the value supplied to them as a parameter. There are two arctangent functions—cleverly named ATAN() and ATN2()—to allow for two different ways of supplying the parameters: either the value of the tangent function, or the equivalent X and Y coordinates of the angle.
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Example
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? ACOS(.5) && returns 1.047, or PI/3
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Usage
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nAngleInRadians = DTOR( nAngleInDegrees )
nAngleInDegrees = RTOD( nAngleInRadians )
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Parameter
|
Value
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Meaning
|
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nAngleInDegrees
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Numeric
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The angle expressed in degrees.
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nAngleInRadians
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Numeric
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The angle expressed in radians.
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DTOR() and RTOD() convert degrees to radians and vice versa.
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Example
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? DTOR( 90 ) && returns 1.57, or PI/2
? RTOD( PI() / 2 ) && returns 90
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PI() returns the static value 3.1415...
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Example
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? PI() && displays 3.1415...etc., depending on SET(DECIMALS)
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View Updates
Copyright 2002 by Tamar E. Granor, Ted Roche, Doug Hennig, and Della Martin. All Rights Reserved.
Activate, Deactivate
These events fire when forms and pages become active or inactive. For a project hook, these events fire when the associated project becomes active or inactive.
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Usage
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PROCEDURE oObject.Activate oObject.Deactivate
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Forms, formsets, toolbars, pages and project hooks all have these events, and their behavior feels a little different for each. Let's start with
toolbars
because they're the simplest. A toolbar's Activate fires when you Show the toolbar. Its Deactivate fires when you Hide it. Period. End of story—even if the toolbar has a control on it that can gain focus. It doesn't matter—Activate doesn't fire even when you land on that control.
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Pages
next
. A page's Activate fires in two situations—when that page comes to the top of the page frame (that is, when you change pages) and when focus on a form is on the page and the form is activated. (A page is not refreshed when it comes to the top; check out Refresh for details and UIEnable for a solution.) A page's Deactivate fires only when a different page in the page frame comes to the top. We can't figure out why the page behaves differently when the form is activated than when it's deactivated. We could argue this one either way—that is, we'd be comfortable with either the page's Activate and Deactivate firing when the form loses focus, or not firing when the form loses focus. But why are they different?
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A form's Activate fires whenever that form comes to the top (conceptually—it may not be physically "on top"). Normally this happens because the
user
clicks on the form while another form has focus or because the tab sequence
brings
focus to a control on the form. A form's Deactivate fires whenever another form gets focus. Show and Hide fire Activate and Deactivate respectively, too.A formset's Activate fires whenever any form in the set is activated. That's right, the formset's Activate fires when a different form comes to the top. In fact, the formset's Activate fires after the Deactivate of the old form and before the new form's Activate. The formset's Deactivate fires only when you Hide the formset or focus moves out of the formset.Now, the
oddball
in this
group
. In VFP 7, Activate and Deactivate were added to the ProjectHook base class, something we'd devoutly hoped for. As you'd expect, Activate fires whenever the associated project gets focus, and Deactivate fires when the project loses focus (say, when you click into the Command Window). These events are most useful when you have multiple projects
open
, because you can make sure each has the appropriate environment, so you use the right controls, store things in the right place, and so forth.
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|
When the project is "rolled up" (collapsed), the project hook's Activate doesn't fire when you click on the title bar. Activate for the project hook of a
collapsed
project does fire when you click on one of the tabs to expand it. We consider the first behavior a bug, since Activate does fire when you click on the title bar of an expanded project.
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This next one, much as we dislike it, we can't bring
ourselves
to call it a bug. When a project is
docked
, the project hook's Activate and Deactivate
methods
don't ever fire. We think that, in this situation, the project is acting like a toolbar, and as we said above, Activate and Deactivate almost never fire for toolbars. So this one is probably by design. Unfortunately, it means we can't do a lot of the things we'd like to do with these events, since we can't count on their firing.
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Destroying an object does not fire its Deactivate event, nor does creating it fire its Activate event. The latter is an issue for project hooks, in one situation. When you choose to have VFP reopen a project at startup (by checking the appropriate check box in the Options dialog), the associated project hook's Activate method doesn't fire on the way in. The
work-around
here is to call the same code from the Init method.
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Example
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* Only the active page in a page frame is refreshed by
* the PageFrame's Refresh method. So, when you move a page
* to the top, it's generally a good idea to refresh it.
* You'd do that in the page's Activate method:
This.Refresh()
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See Also
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Activate Window, Deactivate Window, Form, Formset, Hide, Page, PageFrame, ProjectHook, Show, Toolbar, UIEnable
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View Updates
Copyright 2002 by Tamar E. Granor, Ted Roche, Doug Hennig, and Della Martin. All Rights Reserved.
