A combo box is a control consisting of a display or data entry field and a list of elements which is continuously or temporarily visible.
There are three types of combo box:
Simple |
The display field is modifiable and the list of elements is always visible. |
Dropdown |
The display field is modifiable and the list of elements is visible upon request. |
Dropdown list (or drop list) |
The display field is not modifiable and the list of elements is visible upon request. |
During the layout design phase, this object can be used without any other objects, or can also be used in association with the COMBO_COLUMN object.
If the user wants to place one or more columns in the combo box, all the columns must be included, although only the first will be visible when the program is run.
With dropdown and simple value lists, only the first column is visible. If the value list's style is specified as droplist, however, multiple columns can be displayed, the first of which is always visible.
These columns are used to store values for each item of the combo box, such as the key for a record of which the explicit value is shown in a visible column, for example, or for any other data used while the program is running.
Where a combo box contains one or more columns, a horizontal spin button is displayed to let the developer move between columns. The current column's name is shown in the list, in lower-case characters. This spin button is not visible when the program is run. If an object's property pages are displayed, clicking the button updates the properties on the basis of the current column. The area to the left of the name is used to select the combo box, not the column displayed.
During the execution phase, where the combo box does not contain any explicit columns, it bears the VALUE and CURRENT_VALUE properties.
- The CURRENT_VALUE property refers to the list management (add, modify elements, browse list...).
- The VALUE property fits the content of the display or data entry field in the list.
- It is updated as soon as the user selects an element or enters a value when it is possible.
On the contrary, when the combo box contains at least one column, the combo box has only the VALUE property. The VALUE property of each column placed in the combo box is used to manage the list. Using the CURRENT_VALUE property will have no effect. The list is automatically filled in by the data flow and the level two generation.
Additionally, if the value list contains multiple columns and has the droplist style, you can use the COL_NUM_COMBOBOX_VAL property to specify the column whose value corresponds to the value of the Combo box object. In practice, it is used to specify which of the columns is the key column.
Note: The COMBO_COLUMN object does not exist in Java generation. Placing columns in the Combo box object is only possible for programs which are run with Windows.
Click below for further information about:
the properties,
the events,
the methods.