A Button is a User interface control that you can click to do something by evaluating its OnClick attribute. It usually appear with a beveled edge, with a Title that gives an indication of what they do when clicked. An OnClick attribute can contain almost any kind of expression, including assigning to global variables (which is not usually allowed in Definitions of Variables). It can open or close windows, hide or show variables, and more, to add features that go beyond standard Analytica functionality.
The Ideal Gas Law example model illustrates a simple use of buttons.
This interface contains four buttons:
Find_T. When you press
Find_P, it calculates the pressure in an ideal gas given the volume, number of molecules and temperature, and then sets the value of
P to this value. We say the button has a side-effect of changing the value of variable
Creating a Button
You need Analytica Enterprise or above to create a button. You simply drag the button icon from the toolbar while in edit mode, like any other class of object:
When in browse mode, you click a button simply by pressing the mouse button once with the cursor over the button. In edit mode, mouse over a button to see a green arrow head below the button. Click this is the same as clicking the button in browse mode.
You can also press the tab key until you have selected the button, and then press Enter.
When you click a button, it evaluates its OnClick attribute. The OnClick attribute an expression using the same syntax as the Definition of a variable. From the OnClick expression, you can make use of any Analytica function. Unlike a definition, you can use assignments to global variables or attributes in an Onclick attribute, it does not store or return the final result of evaluation if any.
For example, in the ideal gas law model (ignoring for the moment the flexibility to select units of measurement), the
Find_P script would be an Assignment to
P as follows.
P := n*R*T/V
A picture node, created when you copy/paste and image into a diagram, will also act like a button if you define an OnClick. Click on the image in browse mode, or Alt+click in Edit mode, to evaluate the OnClick attribute (or Script) attribute), just as for a button.
A picture node extent does not have to match the image extent. You can see this in edit mode when you select the node and resize the handles -- the image stays the same size, but the rectangle that defines the node boundaries changes. You will also see this if you select Fill in Set Node Style.... When you mouse click on a picture node, it is the node-extent, not the image extent, that determines the clickable rectangle. Usually it is best to size the node to the image (you can do this by pressing Ctrl+T).
click_x and click_y
You can use the variables
click_y in an OnClick expression. They contain the cursor coordinates when the button or Picture was clicked. Coordinates are in pixels relative to the top-left corner of the button or image for a picture node. This can be handy if you want to do something that varies according to where the user clicks on a button or picture. Coordinates are null if you press the button without a mouse click -- e.g. press enter when the button was selected.
The Script attribute was replaced by the OnClick attribute in Analytica 4.6. The Script attribute still works but is deprecated. The Script attribute contains Typescript language which is subtly (and confusingly) different from the Expression Syntax used in a variable Definition or OnClick attribute -- which is why we replaced it. There are several gotchas with writing button scripts -- especially the confusion that often arises between the assignment operator in expression syntax and typescript assignment, both of which use ":=".
If a button contains both OnClick and Script attributes (not recommended), it executes the OnClick expression before the Script command. Similarly, if a variable contains both an OnChange and Script attribute, it executes the OnChange before the Script attribute. If an error occurs during the evaluation of OnClick or OnChange, it does not execute the Script.
In Analytica 4.6, we introduced the OnClick attribute to replace the Script attribute, which is now deprecated, but still exists in some legacy models.