Input Help 
Data input is of great significance in interactive business applications. In a large number of dialog variants a valid input represents one value from a limited set of values. Users can select a value from a table containing possible values.
Note
Input help is also known as value help, search help, and F4 help.
Example
A simple example of an input help can be illustrated using the airline carrier ID:
To select an airline, the user enters the two letter ID of the airline into a search field. The list of valid letter combinations is limited to the number of available airlines, and the assignment is unique. To facilitate data input, a list of IDs can be provided for the user. The user can then select the required airline from this list. This is implemented with an input help.
Input Help for Web Dynpro ABAP
Web Dynpro ABAP provides you with different types of input help. Which type of input help you choose depends on the application.
Web Dynpro ABAP framework provides you with the following predefined types of input help:
This input help is based on the search help function of the ABAP Dictionary in the SAP system. You use search helps for data elements and structures defined in the ABAP Dictionary, provided these are supported by Web Dynpro.
You can use the object value selection input help if it is not possible to use the ABAP Dictionary for the search, for example, if the value set is to be determined in the Web Dynpro application.
Both these predefined input help types have the advantage that you can fill several fields at a time (for example, two fields for the name of a town and its country).
In addition, you can program your own input help.
You can add further restrictions to your input help by using Select Options.
Permitted values can also be displayed while the user is entering a value in the input field. For more information, see Suggested Values for Input Fields.
You can combine the available input help with various UI elements (e.g. InputField, DropDownByKey). You can define an input help for an InputField in a context attribute that is bound to the value property of the InputField. Once an input help has been integrated, Web Dynpro Framework automatically generates and implements the correct icon for the user to choose to call the input help at runtime. In parallel to this, the F4 key is available for calling input help.
Examples of the Display
Input field with input help:
Input field with input help for date values:
Note
Depending on which date format users have set in the Fixed Values tab, either the Gregorian or Islamic calendar is displayed as input help. For more information see DateNavigator
Caution
You can also use a dropdown list, that is, either UI element DropDownByIndex or DropDownByKey. When you use these UI elements you should keep the value set relatively small. Too many dropdown list boxes in one view may lead to performance bottlenecks.