Tour Preview

Find the Best Demos and Examples

Check out this quick tour to find the best demos and examples for you, and to see how the Felgo SDK can help you to develop your next app or game!

ExpressionRole

A custom role computed from a javascript expression. More...

Import Statement: import Felgo 3.0
Since: Felgo 2.18.1
Inherits:

ProxyRole

Properties

Detailed Description

An ExpressionRole is a ProxyRole allowing to implement a custom role based on a javascript expression.

In the following example, the c role is computed by adding the a role and b role of the model :

 SortFilterProxyModel {
    sourceModel: numberModel
    proxyRoles: ExpressionRole {
        name: "c"
        expression: model.a + model.b
   }
 }

Property Documentation

expression : expression

An expression to implement a custom role. It has the same syntax has a Property Binding except it will be evaluated for each of the source model's rows. The data for this role will be the retuned valued of the expression. Data for each row is exposed like for a delegate of a QML View.

This expression is re-evaluated for a row every time its model data changes. When an external property (not index or in model) the expression depends on changes, the expression is re-evaluated for every row of the source model. To capture the properties the expression depends on, the expression is first executed with invalid data and each property access is detected by the QML engine. This means that if a property is not accessed because of a conditional, it won't be captured and the expression won't be re-evaluated when this property changes.

A workaround to this problem is to access all the properties the expressions depends unconditionally at the beginning of the expression.