The binding API allows you to bind a model to a view. In previous versions of SCADE, we accomplished this in our binding editor, but decided to move it into code. We are pursuing multiple goals with this

  • Binding becomes easier to manage

  • Ability to version control and diff

  • Becomes the basis for evolving it into a declarative UI framework similar to Nick Lookwoods [Layout](🔗), SwiftUI or Flutter's UI

Moreover, the binding API was designed to provide **full type safety**, greatly reducing errors and providing auto completion.

The Binding Editor is still working

You currently - in this and the next releases - have the choice to use the binding editor or the binding api. However, we are phasing out the binding editor and will remove it in some later release.

**So for new apps, please use the binding API.**

# Introduction

When you establish a model view binding, you create a relationship between data stored in a variable and a UI component. So whenever the variable changes, or the UI changes, the variable or the UI control are updated automatically.

# Example 1 - Binding a variable to a label control

### Creating the model

A simple Swift class **City** serves as the model

  • Inherit from **EObject**

  • Add attribute **@objcMembers** - The objcMembers attribute tells Swift to make all methods and variables inside this class available to Objective - C. This is important as UiKit relies on Objective - C.

We create an instance variable of you City in our class and annotate it with **@objc **and **dynamic**.

### Creating the view

In this simple example, the view is an iOS / android label. We used the page editor to add the label into the model of the screen and now create a reference to it using the **getWidgetByName** method:

### Binding the variable to the view

We now use the new binding syntax to create a source and a destination and bind them together

  • we use the **from** method to specify the object we refer to

  • we use the **select** method to select a property from the object

  • we use the **\ **operator to refer the parent structure.

The fantastic thing about the binding syntax? It's **fully type safe**.

When we run this little example, we can a nicely working binding

# Example 2 - Binding objects to a List control

Our second example demonstrate the typical binding of a list of objects (with its properties) to a list control.

### Creating the model

The model is a list of cities called cityList of type CityList:

### Creating the view

This time, we want to have a **UITableView** the view. **SCDWidgetsList** is the SCADE name for it. The id of this control is list1. Its the default name that got created when we dragged and dropped the label into the list control

### Two step binding

The binding for collections is currently done in two steps

  1. Binding the list of data objects to the list of graphical elements in the list control

  2. Binding the attribute of the data object to the attribute of the graphical element

Step 1 - Bind array of data object to list controls internal list:

  • bind **cities** to **items**

  • **Items** is a property of a list control and represents the data the list control is using

  • You need to use the **cast** method to map between non-identical data types

Step 2 - Bind array of data object to list controls internal list:

  • bind **cityName** to the** text attribute** of a label

  • in the current version of the API, we reference the label by number. Its the first element in the row **at(0)**

  • the **.all** parameter is used to select all elements.

  • Items is a property of a list control and represents the data the list control is using

The final app

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# Outlook for July 2019 release

We released version 1 of the binding api. In our next release, we will add an improvement that shortens the two steps of binding to one step, greatly simplifying our 2nd example