Slider

Slider puts a slider on the screen; the operator writes a value to a variable by dragging the handle. It is used for setting a setpoint, giving a speed reference, or dialling in a ratio by hand.

It is offered on rect alone: you set aside the area the slider occupies by drawing a rectangle.

Configuration: no form, an expression

Most types give you a Tag form with fields to fill in. Slider does not — its only mode is Expressions, and the expression itself builds the slider.

The expression runs in an isolated frame of its own, with these already in place:

What	Description
_container	The empty div the slider is drawn into
inscadaApi	The client API for reading and writing values and calling the platform
noUiSlider · wNumb	The slider library and its number-formatting helper, already loaded on the page

So the expression does two things: it builds the slider inside _container, and it writes the value to the variable through inscadaApi as the handle moves. The bounds, the step, the orientation and when the value is written are all decided in that code.

Write the value when the handle is released

Wire the slider to write on every change and dragging the handle from one end to the other sends every intermediate value to the field — on a speed reference that is tens of needless setpoints to the device. noUiSlider offers two separate events for this: one that fires continuously while dragging, and one that fires once when the handle is released. For a slider used for control, use the second.

Write permission, locks and signatures

Writing from a slider is an ordinary variable write and is subject to the same controls:

• Refused if the user does not hold the permission to write values.
• Refused if the variable carries an Operation Lock.
• Where the installation requires a signature, a signing box appears before the write and the operation is recorded in the audit trail along with who performed it.

An embedded slider versus a pop-up one

There are two separate things here and they are easy to confuse:

	The Slider type	Click → Set → Slider style
How it is configured	By writing an expression	From a form — variable, bounds, step
Where it sits	On the screen, always visible	In a window that opens when clicked
When it suits	A setpoint the operator adjusts often	A value changed rarely, that should not be touched by accident

If you want a slider without writing code, the second is almost certainly what you are after: a Click binding with the Set action and the Slider presentation style. Detail: Click and mouse events.

It is also the one to choose to protect a value against accidental change: a handle sitting on the screen is easy to nudge.

How it works at run time

Slider takes no part in the screen’s periodic evaluation loop. Like Chart and Datatable it renders in an isolated frame of its own and fetches its own data. Detail: Element Editor.

Related

• Click and mouse events — the form-configured slider, and the other ways to write a value
• Element Editor — the fields every binding form shares
• Bar and Scale — the display-only counterpart that writes nothing