step-21-expression-binding-typescript-8d67ba2.md

Step 21: Expression Binding (TypeScript)

Sometimes the predefined types of OpenUI5 are not flexible enough and you want to do a simple calculation or formatting in the view - that is where expressions are really helpful. We use them to format our price according to the current number in the data model.

Preview

The price is now formatted according to its number

Coding

You can view all files at OpenUI5 TypeScript Walkthrough - Step 21: Expression Binding and download the solution as a zip file.

webapp/view/InvoiceList.view.xml

We add the numberState attribute to the ObjectListItem control invoices list view. We use the = symbol to initiate an expression binding and specify that the number in numberState appears in red if the price is greater than 50, otherwise in green.

<mvc:View
    controllerName="ui5.walkthrough.controller.InvoiceList"
    xmlns="sap.m"
    xmlns:core="sap.ui.core"
    xmlns:mvc="sap.ui.core.mvc">
    <List
        headerText="{i18n>invoiceListTitle}"
        class="sapUiResponsiveMargin"
        width="auto"
        items="{invoice>/Invoices}">
        <items>
            <ObjectListItem
                core:require="{
                    Currency: 'sap/ui/model/type/Currency'
                }"
                title="{invoice>Quantity} x {invoice>ProductName}"
                number="{
                    parts: [
                        'invoice>ExtendedPrice',
                        'view>/currency'
                    ],
                    type: 'Currency',
                    formatOptions: {
                        showMeasure: false
                    }
                }"
                numberUnit="{view>/currency}"
                numberState="{= ${invoice>ExtendedPrice} > 50 ? 'Error' : 'Success' }"/>
        </items>
    </List>
</mvc:View>

Expression binding can do simple calculation logic like the ternary operator shown here.

The condition of the operator is a value from our data model. A model binding inside an expression binding has to be escaped with the $ sign as you can see in the code. We set the state to "Error" (the number will appear in red) if the price is higher than 50 and to "Success" (the number will appear in green) otherwise.

Expressions are limited to a particular set of operations that help formatting the data such as Math expression, comparisons, and such. You can look up the possible operations in the documentation.

Conventions

• Only use expression binding for trivial calculations.

Related Information

Expression Binding