Lecture 19. Using Data Controls

To display and edit data from a database, use the components on the Data Controls page of the Component palette. Data controls include components such as TDBGrid for displaying and editing all specified records and fields in a table, and TDBNavigator for navigating among records, deleting records, and posting records when they change.

Figure 4.1 Data Controls Component palette

The following table summarizes the data controls in order from left to right as they appear on the Component palette:

Table 4.1 Data controls

Data control	Description
TDBGrid	Displays information from a data source in a spreadsheet-like grid. Columns in the grid can be specified at design time using the Fields Editor or at run time (dynamically bound).
TDBNavigator	Provides buttons for navigating through data obtained from a data source. At design time, you can choose to include one or more buttons to navigate through records, update records, post records, and refresh the data from the data source.
TDBText	Displays data from a specific column in the current data record.
TDBEdit	Uses an edit box to display and edit data from a specific column in the current data record.
TDBMemo	Displays memo-type database data. Memo fields can contain multiple lines of text or can contain BLOB (binary large object) data.
TDBImage	Displays graphic images and BLOB data from a specific column in the current data record.
TDBListBox	Displays a list of items from which a user can update a specific column in the current data record.
TDBComboBox	Combines a TDBEdit control with an attached list. The application user can update a specific column in the current data record by typing a value or by choosing a value from the drop-down list.
TDBCheckBox	Displays a check box. If the value in the indicated column of the current record matches the text of the check box’s ValueChecked property, the box is checked.
TDBRadioGroup	Offers a mutually exclusive set of options to enter into a specific column in the current data record in the form of radio buttons.
TDBLookupList	Displays a list of items from which a user can update a column in the current data record. The list of items is looked up in a specific column in another dataset.
TDBLookupCombo	Combines a TDBEdit control with a dropdown version of TDBLookupList. The application user can update a field in the current database by typing a value or by choosing a value from the drop-down list that is looked up in a specific column in another dataset.

Most data controls are data-aware versions of standard components. Some, such as TDBGrid and TDBNavigator, are data-aware, but differ from standard components insignificant, useful ways. A data-aware control derives display data from a database source outside the application, and can also optionally post (or return) data changes to a data source. Data controls are data-aware at design time, meaning that when you connect a component to an active data source while building an application, you can immediately see live data in the controls. You can use the Fields Editor to scroll through records at design time to verify that your application is making the right database connections without requiring you to compile and run the application, but you cannot modify data at design time.

This chapter describes basic features common to all Data Control components, then describes how and when to use individual components.

Дата добавления: 2015-10-23