ch17.htm

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differences between a list box and a combo box.</P>
<P>
<H3><A NAME="Heading15"></A>The DBCheckBox Component</H3>
<P>You use the DBCheckBox primarily to display the contents of a database field containing
logical data (True/False, Yes/No, On/Off). Set the ValueChecked property to a string
that should be used to check for a match against the contents of the field. For example:</P>
<P>
<CENTER>
<H1>DBCheckBox1.ValueChecked := `On';</H1>
</CENTER>
<P>In this case, if the associated field contains the value On, the DBCheckBox will
be checked. If the field contains a value other than the one specified, the check
box will not be checked. You can supply more than one value to check in the ValueChecked
property. For example:</P>
<P>
<PRE>DBCheckBox1.ValueChecked := `On;Yes;True';
</PRE>
<P>If the value of the associated field contains any one of these values, the check
box will be checked. The ValueUnchecked property works in exactly the same way except
that any values matching the contents of ValueUnchecked will cause the check box
to be cleared (unchecked). When specifying values for both ValueChecked and ValueUnchecked,
the check box state will be indeterminate (grayed check mark) for field values that
don't match.</P>
<P>
<H3><A NAME="Heading16"></A>The DBRadioGroup Component</H3>
<P>The DBRadioGroup component works much like the DBListBox and DBComboBox components.
You supply the items for the radio group and when an item is selected, the value
(text) associated with that radio button is written to the associated field in the
database.</P>
<P>The Values property holds the current value of the field in the database. You
can use the Values property to substitute the display string in the radio group box
with a different string. For example, you might have a radio group box with radio
buttons labeled Yearly, Quarterly, and Monthly. Your database, however, might store
codes such as Y, Q, and M instead of the full names. Given that scenario, you could
set the Values property (a string list) like so:</P>
<P>
<PRE>Y
Q
M
</PRE>
<P>Now, when a radio button is selected, the one-letter code will be written to the
database field instead of the display string of the selected radio button. If the
Values property is empty, the display string of the radio button will be written
to the database when a radio button is clicked.</P>
<P>
<H3><A NAME="Heading17"></A>The DBLookupListBox and DBLookupComboBox Components</H3>
<P>The DBLookupListBox component enables you to display a list of field values from
a lookup field. Unlike the DBComboBox component, the list isn't provided by you;
it is provided by a separate dataset. Set the DataSource and DataField properties
to the dataset and field where the selection will be written. Set the ListSource
and ListField properties to the lookup field from which the list should be populated.</P>
<P>The DBLookupComboBox works just like the DBLookupListBox. In addition, the DropDownAlign,
DropDownRows, and DropDownWidth properties control how the drop-down list appears.</P>
<P>
<H3><A NAME="Heading18"></A>The DBRichEdit Component</H3>
<P>The DBRichEdit component enables you to display and edit a rich text memo field
in a dataset. The AutoDisplay property and LoadMemo methods of this component work
exactly as they do for the DBMemo component.</P>
<P>
<H3><A NAME="Heading19"></A>The DBCtrlGrid Component</H3>
<P>DBCtrlGrid is a component that enables you to create custom scrollable grid components.
You can place any data components you want on the first cell of the DBCtrlGrid (or
any other components for that matter), and Delphi will duplicate those components
for each record in the dataset.</P>
<P>An illustration helps this explanation make more sense. Figure 17.12 shows a form
containing a DBCtrlGrid component that has been aligned so that it fills the form's
client area. The DBCtrlGrid contains a DBEdit, a DBMemo, and a DBImage. All the data
components are placed on the first cell of the grid. The second cell contains a hatch
pattern to tell you that you can't place components on that cell. Figure 17.13 shows
the same form when the application is running.</P>

<P><A HREF="javascript:popUp('28671712.gif')"><B>FIGURE 17.12.</B></A><B> </B><I>A
form at design time containing a DBCtrlGrid component.</I></P>

<P><A HREF="javascript:popUp('28671713.gif')"><B>FIGURE 17.13.</B></A><B> </B><I>The
same form at runtime.</I></P>

<P>The DBCtrlGrid has a few properties worth mentioning. You use the Orientation
property to determine where the scrollbar is to be placed and how the component acts
when the scrollbar is clicked (the DBCtrlGrid in Figures 17.12 and 17.13 has the
Orientation set to goHorizontal). You use the PanelWidth and PanelHeight properties
to set the width and height of a cell in the grid. The RowCount property determines
how many records to show at one time.</P>

<P>The DBCtrlGrid component has one event, OnPaintPanel. This event is fired each
time a grid cell needs painting. You can respond to this event in order to draw on
the background of the panel. This pertains only to the panel's background. Any controls
on the grid will be painted automatically, so you don't have to worry about them.</P>
<P>
<H3><A NAME="Heading20"></A>Other Data Components</H3>
<P>DBChart is a charting component included with the Professional and Client/Server
versions of Delphi. This component is not only powerful, but also complex. I can't
begin to explain everything the DBChart component does, so you'll have to experiment
with it to discover all that it is capable of.</P>
<P>The Client/Server version of Delphi includes a tab named Decision Cube that contains
six additional components. These components enable you to do complex data analysis
such as cross tabulation of tables and graphs, drill down, pivot, and aggregation.
A discussion of these components wouldn't be productive here, but I want you to be
aware that these components exist in the Client/Server version of Delphi.</P>
<P>
<H2><A NAME="Heading21"></A>Summary</H2>
<P>Well, that about sums up the art of building database forms. (Actually, I'm being
facetious because I've just scratched the surface of database form creation and design.)
Use the Database Form Wizard for quick and easy database forms. Create database forms
from scratch for more flexibility. Either way you go, building good database forms
takes time and experience to master. It isn't something that you can be great at
overnight. On the other hand, it isn't terribly difficult, either. Keep working at
it and you'll be a database whiz in no time. The important thing is knowing the data
components available to you as you build your forms.</P>
<P>
<H2><A NAME="Heading22"></A>Workshop</H2>
<P>The Workshop contains quiz questions to help you solidify your understanding of
the material covered and exercises to provide you with experience using what you
have learned. You can find the answers to the quiz questions in Appendix A, &quot;Answers
to the Quiz Questions.&quot;</P>
<P>
<H3><A NAME="Heading23"></A>Q&amp;A</H3>

<DL>
	<DT></DT>
	<DD><B>Q I like the way the Database Form Wizard saves me time, but I don't like
	the way the components are arranged on the form. What do you suggest?</B>
	<P>
	<DT><B></B></DT>
	<DD><B>A </B>Run the Database Form Wizard to create components for any fields you
	want on your form. Then manually rearrange the components to make the form look the
	way you want. The Database Form Wizard just gives you a head start. You can do anything
	you want with the form after the Database Form Wizard has done its job.
	<P>
	<DT></DT>
	<DD><B>Q When using the Database Form Wizard, does it matter whether I create a form
	using TTable or TQuery objects?</B>
	<P>
	<DT><B></B></DT>
	<DD><B>A </B>It all depends on the type of database you are talking to. If you are
	dealing with a local database such as Paradox or dBASE, you will probably use a TTable.
	If you are dealing with a client/server database, you will likely use a TQuery.
	<P>
	<DT></DT>
	<DD><B>Q Is there any limit to the number of DataSource, Table, and Query components
	I can have on my form?</B>
	<P>
	<DT><B></B></DT>
	<DD><B>A </B>There's no absolute limit, although there are practical limits to how
	many datasets you can work with at one time.
	<P>
	<DT></DT>
	<DD><B>Q I noticed the DBEdit component doesn't have a Text property like the regular
	Edit component has. Why is that?</B>
	<P>
	<DT><B></B></DT>
	<DD><B>A </B>The DBEdit component doesn't have a Text property because the component
	contents are obtained from a dataset. To access the contents of a DBEdit component,
	use the dataset's GetFieldByName method and the Value property of TField.
	<P>
	<DT></DT>
	<DD><B>Q Do I have to use a DBNavigator to enable my users to browse the database?</B>
	<P>
	<DT><B></B></DT>
	<DD><B>A </B>No, you could provide your own buttons and then write code to move the
	database cursor when the buttons are clicked. Using a DBNavigator is much easier,
	though.
	<P>
</DL>

<PRE><B>	Q	My database contains a number of large images in BLOB fields, and it seems to take a long time to display the images. Is there something I can do to make the images draw faster?</B>
</PRE>

<DL>
	<DT></DT>
	<DD><B>A </B>Make certain that you have the QuickDraw property set to True. Your
	images will draw faster, but they might not look as good.
	<P>
</DL>

<H3><A NAME="Heading24"></A>Quiz</H3>

<DL>
	<DT></DT>
	<DD><B>1. </B>What's the fastest and easiest way to create a database form?
	<P>
	<DT></DT>
	<DD><B>2. </B>How do you control the order and number of columns that appear in a
	DBGrid component?
	<P>
	<DT></DT>
	<DD><B>3. </B>What component enables you to display a dataset in table format?
	<P>
	<DT></DT>
	<DD><B>4. </B>How can you add or remove buttons from a DBNavigator?
	<P>
	<DT></DT>
	<DD><B>5. </B>What component do you use to display BLOB image data?
	<P>
	<DT></DT>
	<DD><B>6. </B>What property is common to all data-aware components?
	<P>
	<DT></DT>
	<DD><B>7. </B>What property is used to select the field that a data component is
	linked to?
	<P>
	<DT></DT>
	<DD><B>8. </B>Can you rearrange the columns in a DBGrid component?
	<P>
	<DT></DT>
	<DD><B>9. </B>Which component is used to edit and display text fields in a database?
	<P>
	<DT></DT>
	<DD><B>10. </B>What does BLOB stand for?
	<P>
</DL>

<H3><A NAME="Heading25"></A>Exercises</H3>

<DL>
	<DT></DT>
	<DD><B>1. </B>Create a new application that shows the contents of the VENDORS.DB
	table (DBDEMOS database).
	<P>
	<DT></DT>
	<DD><B>2. </B>Modify the application in step 1 so that only the VendorName, City,
	State, and Phone fields are displayed.
	<P>
	<DT></DT>
	<DD><B>3. </B>Delphi Professional and Client/Server owners: Create a master/detail
	form from the IBLOCAL database (install Local InterBase from the Delphi CD if necessary).
	Use the EMPLOYEE table as the master and the EMPLOYEE_PROJECT table as the detail
	table. (Hint: Use the EMP_NO field to link the tables.)
	<P>
	<DT></DT>
	<DD><B>4. </B>Create a database form that uses a DBCtrlGrid component to browse a
	table. Use any table and include any fields you like.
	<P>
	<DT></DT>
	<DD><B>5. </B>Create a database form by hand (not using the Database Form Wizard)
	using any table and any fields you like. Add a DBNavigator component to browse the
	table.
	<P>
	<DT></DT>
	<DD><B>6. </B>Remove all buttons from the DBNavigator used in step 5 except the First,
	Next, Prior, and Last buttons.
</DL>

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