ch17.htm

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	Change the DataSet property to Table1.
	<P>
	<DT></DT>
	<DD><B>5. </B>Place a DBNavigator on the panel at the top of the form. Change its
	DataSource property to DataSource1.
	<P>
</DL>



<BLOCKQUOTE>
	<P>
<HR>
<strong>TIP:</strong> You can set the DataSource property quickly by double-clicking the
	value column next to the property in the Object Inspector. Delphi will cycle through
	the available DataSource components each time you double-click. 
<HR>


</BLOCKQUOTE>


<DL>
	<DT></DT>
</DL>

<P>Your form now looks like Figure 17.10.</P>

<P><A HREF="javascript:popUp('28671710.gif')"><B>FIGURE 17.10.</B></A><B> </B><I>The
form in the initial stages.</I></P>

<P>Now you need to add some data components to display the table's data. As you work
through this exercise, you might want to refer to Figure 17.7 to see the result.
Do the following:</P>
<P>

<DL>
	<DT></DT>
	<DD><B>1. </B>Place a DBEdit component on the main part of the form along the left
	side. Change the Name property to NameEdit; change the DataSource property to DataSource1;
	change the DataField property to NAME (choose NAME from the drop-down list).
	<P>
	<DT></DT>
	<DD><B>2. </B>Place a Label component above the DBEdit you created in step 1 (use
	a regular Label component from the Standard page of the Component palette, not a
	DBText component). Change its Caption property to Name.
	<P>
	<DT></DT>
	<DD><B>3. </B>Repeat steps 1 and 2 and add DBEdits and Labels for the SIZE, WEIGHT,
	and AREA fields of the table. Make certain that you change the Name property and
	DataField property with respect to each field's name.
	<P>
	<DT></DT>
	<DD>In the next two steps, you depart from Figure 17.7 and place the component for
	the BMP field to the right of the components you just placed. It makes more sense
	for it to be there rather than below the existing components.
	<P>
	<DT></DT>
	<DD><B>4. </B>Place a DBImage component on the form to the right of the edit components.
	Change the Name property to BMPImage, and change the DataSource property to DataSource1
	and the DataField property to BMP.
	<P>
	<DT></DT>
	<DD><B>5. </B>Place a Label component above the DBImage and change its Caption property
	to Picture (the field name is BMP, but the word Picture is more descriptive).
	<P>
</DL>

<P>Now your form looks like the one shown in Figure 17.11.</P>
<P><A HREF="javascript:popUp('28671711.gif')"><B>FIGURE 17.11.</B></A><B> </B><I>The
form with the data components in place.</I></P>

<P>Now you need to set the size of the DBImage component. Although you can't always
be sure that each image will be the same size in every database, you can be certain
in this case. You might guess at the size of the bitmap, but a better solution would
be to set the size with a live image in the component. That's easy enough to fix.
Click on the Table component and set its Active property to True. The image for the
first record in the table is displayed. Now you can size the DBImage as needed to
match the bitmap size.</P>
<P>You have nearly completed the form, but there's one more thing you should do.
To imitate the form that the Database Form Wizard created, you need to open the table
when the form is created:</P>
<P>

<DL>
	<DT></DT>
	<DD><B>1. </B>First, set the Active property of the Table to False (you just set
	it to True a minute ago).
	<P>
	<DT></DT>
	<DD><B>2. </B>Now select the form itself in the Object Inspector. (Remember that
	to select the form, you click on the panel and then press the Esc key on your keyboard.
	You can also select the form from the Component Selector at the top of the Object
	Inspector.)
	<P>
	<DT></DT>
	<DD><B>3. </B>Switch to the Events page and create an event handler for the OnCreate
	event. Type this line of code in the event handler:
	<P>
</DL>

<PRE>Table1.Open;
</PRE>
<P>That's it. Your new form is finished. Click the Run button to test your new creation.
It will behave exactly like the first form you created with the Database Form Wizard.</P>
<P>
<H2><A NAME="Heading6"></A>A Closer Look at the Data Components</H2>
<P>At this point, a quick look at the data components is in order. I'll give a brief
overview of each component and highlight each one's key properties and methods. Most
of the data components are derived from a standard component and have many of the
properties associated with that type of component. I will discuss only the properties
that are specific to the data version of each component.<B></B></P>
<P>
<H3><A NAME="Heading7"></A>Properties Common to Data Components</H3>
<P>All the data components have properties in common. For example, all the components
have a DataSource property. This property is used to link a data component with a
data source, which is itself linked to a dataset. You have been using the DataSource
property a lot in the past couple of days, so you should have a good idea of how
it works.</P>
<P>Most data components also have a DataField property. You use this property to
hook the data component to a particular field in the dataset. You saw how the DataField
property is used when you built a database form from scratch. When you hook a data
component to a field in the dataset, the contents of that field are directly displayed
in the data component. In the case of Tables (and Queries if the RequestLive property
is True), this means that editing the data in the data control will result in changes
to the data in the database.</P>
<P>Most data components also have a Field property. You use the Field property to
gain access to a component's contents programmatically. For example, to change the
contents of a DBEdit component, you can do the following:</P>
<P>
<PRE>NameEdit.Field.AsString := `Clown Fish';
</PRE>
<P>You can also change the field's display characteristics or other TField properties
through the Field property.</P>
<P>You can use the ReadOnly property to prevent the user from editing the data in
a data component that enables editing (DBGrid and DBEdit, for example).</P>
<P>
<H3><A NAME="Heading8"></A>The DBGrid Component</H3>
<P>The DBGrid component displays a dataset in tabular, or spreadsheet, format. One
of the most important properties of the DBGrid is the Columns property. This property
enables you to change the number and order of the columns that appear in the grid.
You can add, remove, and order columns using the Columns Editor.</P>
<P>To invoke the Columns Editor, right-click on the grid and choose Columns Editor
from the context menu. You can also click the ellipsis button next to the Columns
property in the Object Inspector. Using the Columns Editor, you can add columns,
remove columns, and arrange the order of columns. For example, a dataset might contain
a dozen fields, but you might want to view only half those fields in the DBGrid.
Using the Columns Editor, you can hide the fields that you don't want to see.</P>


<BLOCKQUOTE>
	<P>
<HR>
<strong>NOTE:</strong> Don't confuse the DBGrid Columns property (modified with the Columns
	Editor) with the Table component's FieldDefs property (modified with the Fields Editor).
	The FieldDefs property of the Table component controls which columns are actually
	contained in the dataset. The Columns property only affects which fields are <I>visible</I>
	in the grid.
<HR>


</BLOCKQUOTE>

<P>The DefaultDrawing property indicates whether VCL draws the cells in the grid
or the grid cells are owner-drawn. If DefaultDrawing is False, you must respond to
the OnDrawColumnCell and OnDrawDataCell events to provide drawing for the cells.</P>
<P>The Options property enables you to set the display and behavior options for the
grid. Using this property, you can turn off column titles, allow or disallow column
sizing, turn row and column lines on or off, and so on.</P>
<P>The TitleFont property enables you to set the font for the column titles. You
use the Font property to set the font for the grid cells.</P>
<P>The DBGrid has only two public methods. When using an owner-drawn grid, you can
call the DefaultDrawColumnCell and DefaultDrawDataCell methods to ask VCL to draw
the cell for you. This is useful if you are owner-drawing particular columns but
you want default drawing behavior for the rest of the columns.</P>
<P>The DBGrid component has several events, most of which pertain to cell editing
and data navigation. I won't list the events here because it is obvious from their
names what functions they perform.</P>
<P>
<H3><A NAME="Heading9"></A>The DBNavigator Component</H3>
<P>The DBNavigator component enables the user to browse a dataset record by record.
The navigator provides buttons for first record, next record, previous record, last
record, insert record, delete record, edit record, cancel edits, post edits, and
refresh. This component is nearly automatic in that most of the time all you have
to do is drop it on the form, hook it to a DataSource, and forget about it.</P>
<P>The ConfirmDelete property, when set to True, causes a dialog box to be displayed
whenever the user clicks the Delete button. You set the Hints property to True to
enable fly-over hints for each button on the navigator. The VisibleButtons property
is a set that enables you to control which buttons show up on the navigator. You
can add or remove buttons at design time or runtime.</P>
<P>The DBNavigator has only one method of interest and one event. You can use the
BtnClick method to simulate a button click on the navigator. You can use the OnClick
event to detect a click on the navigator. You rarely have to use OnClick, however,
because the navigator already knows what to do when its buttons are clicked.</P>
<P>
<H3><A NAME="Heading10"></A>The DBText Component</H3>
<P>The DBText component is the data-aware version of the standard Label component.
It provides a way of displaying data from a field without enabling the user to modify
the data. This component provides no database-specific properties, methods, or events
other than those common to all data components.</P>
<P>
<H3><A NAME="Heading11"></A>The DBEdit Component</H3>
<P>The DBEdit component provides an edit control that is linked to a field in a dataset.
You used a DBEdit earlier today when you created a database form from scratch. The
DBEdit component, like the DBText component, doesn't have any database-specific properties,
methods, or events other than those common to all data components.</P>
<P>
<H3><A NAME="Heading12"></A>The DBMemo Component</H3>
<P>The DBMemo is the data version of the standard Memo component. You can use this
component to display data contained in database fields that contain large amounts
of text. The AutoDisplay property controls whether the data in the dataset field
is automatically displayed when the cursor changes to a new record.</P>
<P>When AutoDisplay is True, the data is automatically displayed. When AutoDisplay
is False, the user must double-click the DBMemo to display the data (or press Enter
when the control has focus). To force the memo to display its contents through code,
you use a related method called LoadMemo. This method is appropriate only when AutoDisplay
is False.</P>
<P>
<H3><A NAME="Heading13"></A>The DBImage Component</H3>
<P>The DBImage component is used to display binary large object (BLOB) data that
is stored in image format. DBImage isn't necessarily a read-only component. You can
change an image by pasting an image from the Clipboard or by using the Picture property
to load a file from disk. The following code will change the image at runtime:</P>
<P>
<PRE>DBImage1.Picture.LoadFromFile(`peregrine.bmp');
</PRE>
<P>The main DBImage properties control how the image is displayed. They are described
as follows:</P>
<P>

<UL>
	<LI>The AutoDisplay property works exactly as described for the DBMemo component.
	<P>
	<LI>The LoadPicture method can be used to display the image when the AutoDisplay
	property is False.
	<P>
	<LI>The Picture property enables access to the image itself and works the same as
	it does for components such as the standard Image component.
	<P>
	<LI>The Center property determines whether the image is centered in the DBImage window.
	<P>
	<LI>The Stretch property determines whether the image will be stretched to fit the
	current size of the DBImage window or whether it will be displayed in its original
	size. If Stretch is False, part of the image will be clipped if the image is too
	large for the DBImage window.
	<P>
	<LI>The QuickDraw property determines whether to apply a palette to the image when
	it is displayed. When QuickDraw is True, no palette is used. When QuickDraw is False,
	a palette is used to display the image, which results in higher quality but slightly
	poorer performance when displaying images.
</UL>

<P>Methods of the DBImage component include CutToClipboard, CopyToClipboard, and
PasteFromClipboard. These methods do exactly what their names indicate.</P>
<P>
<H3><A NAME="Heading14"></A>The DBListBox and DBComboBox Components</H3>
<P>The DBListBox component is, for the most part, a standard list box. What distinguishes
it is that when the user selects an item in the list box, the selected item is written
to the corresponding field in the dataset (set by the DataField property). To provide
the strings the user can select from, you add strings to the Items property just
as you do for a regular ListBox component. It is important to realize that the strings
for the list box don't come from the database (that's what the DBLookupListBox is
for).</P>
<P>The DBComboBox works in exactly the same way as the DBListBox except for the obvious