Mutual data binding enables interaction between UI elements and context elements. The view, which contains the UI elements, is always bound against the context of its assigned controller. If a data binding of context element and UI element property is defined, the changes of the UI element property are directly transferred to the context and vice versa. These changes are also adopted by the properties of other UI elements of the same view if the are bound to the same context element. More complex UI elements – for example, the Table UI element or Tree UI element – can be bound to a context node that represents a collection. Therefore, these UI elements can display the complete data and content of the node.
By storing a reference to a context element, data can be passed directly from the context to the UI element and back. This reference is created by specifying an entry that is similar to a path – for example, MonthsOfYear.MonthName– as a value of a bindable UI element property. A period separates the individual context elements - for example, MonthsOfYear.MonthName. See Code Examples of Data Binding.
The SAP NetWeaver Developer Studio provides graphical support of the context elements and allows application developers to assign the context nodes and context attributes to the corresponding UI element properties. This means that the data transport between the context element and the UI element does not require an explicit implementation.
There are different data binding concepts for the individual UI elements. The following general rules apply:
Data binding with the
same data types or convertible data types
The type of context attribute must be compatible with the property type. This means that the types must be either identical or the property of the UI element must be of the type String and convertible. In the latter case, the type of the context attribute (for example, InputField value) does not matter.
Data binding of UI
elements with dynamic or static characteristics
It is pointless to bind certain UI elements - for example, properties with a static characteristic - to a corresponding context. This is why the ID of a UI element, which a label control refers to, cannot be bound to a context. However, the data source of a table UI element, which is usually created dynamically and also represents a structure, must be bound to a context.
Data binding of UI
elements with non-scalar characteristics
Several properties of UI elements do not have scalar characteristics, but resemble a collection of elements. These elements are not bound to an individual root attribute but to the context attribute of a multiple node. A multiple node can be a dropdown list box, for example. Each element of the multiple node contains a different instance of the context attribute. Therefore, several elements appear in the selection list.
Data binding to the
There are also properties that refer to a complete node and not only to one of its attributes. This applies to the data source of a table: The elements of the bound node correspond to the table rows, its attributes to the columns.
Note that the IDs of the UI elements are not bound. The same applies to these properties that represent the names of an action and can be executed when an event occurs - for example, CheckBox.onToggle.
Certain properties, however, can be bound to any type of the context attribute if they are defined as convertible. These are, for example:
All other properties can only be bound to a context attribute of the same data type.
The checkbox group UI element can be bound, for example, to the context attribute MonthName of the context node MonthsOfYear using the bindTexts property.
The CheckBoxGroup UI element stores the reference to the context attribute. Therefore, it automatically receives the context values and can overwrite the context with new values. The application developer can initializes the value of the context attribute in the wdDolnit method.