Contextual variables
Contextual variables are similar to global variables except they are only referenced on the screen where you create them. Although it’s possible to set the user's name to a variable to reference throughout your app, there are still advantages to the fact that contextual variables cannot be used on other screens.
Sometimes you have functionality you want to use on multiple screens that is variable driven. For example, many apps use pop-up dialog boxes to confirm things like deleting a record. A common way to implement is to set a Contextual variable to true when the user selects the delete button. You do that by setting the OnSelect property of the button to the following.
UpdateContext({varShowPopUp: true})
You then set the Visible property of the pop-up controls to varShowPopUp. This is similar to the example from the global variables. The major difference is reusability. If you copy the controls (using Ctrl+C) to another screen, then you will have two instances of varShowPopUp. These two instances use the same name, but can have different values. The value of varShowPopUp on screen1 does not affect the value of varShowPopUp on screen2 because each contextual variable, even when they have the same name, are scoped to the screen they are on.
Typically reusing variable names is not recommended because it can be confusing, but it’s great if you want to reuse functionality independently on different screens.
If you are in doubt about whether you should use global or contextual variables, typically global variables are the default answer. Global variables are available everywhere, making them the most flexible.
One unique behavior of the UpdateContext function is that you can declare more than one variable at a time. This is not possible with the Set function. To create more than one context variable with a single formula, use a comma between the variables.
UpdateContext({varCount: 1, varActive: true, varName: User().FullName})
Note
In the previous module, we mentioned that using the User() function inline will unnecessarily slow down your app and for that reason a global variable should be used OnStart. While using a contextual variable to store User information will improve performance over inline use of the User() function, it is ultimately less performative than a global variable, as you will still be calling on the data source each time that page opens. As such, it is recommended to store User information in a global variable.
To do the same thing with Global variables, you would use the following.
Set(varCount, 1);Set(varActive, true);Set(varName, User().FullName)
In the next unit, you will learn about storing tables of data in a collection variable.