database

Odnośniki

Smutek to uczucie, jak gdyby się tonęło, jak gdyby grzebano cię w ziemi.

You can use the navigation bar to move from record to record in the
database, insert a record, or delete a record. The Update command does not work yet.
Close the application when you’re ready to continue.
Adding a button
This section describes how to add an Update Now button to the application. This
button is used to apply any edits that a user makes to the database, such as editing
records, adding new records, or deleting records.
To add a button:
1 From the Standard page of the Component palette, drop a TButton onto the form.
(Select the component then click the form next to the navigation bar.)
2 Set the button’s Action property to Action1.
The button’s caption changes to Update Now! When you run the application, it
will be grayed out until an event handler is added to make it work.
Displaying a title and an image
You can add a company title and an image to make your application look more
professional:
1 From the Standard page of the component palette, drop a TLabel component onto
the form (named Label1 by default).
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2 In the Object Inspector, change the label’s Caption property to World Corp or
another company name.
3 Change the company name’s font by clicking the Font property. Click the ellipsis
that appears on the right and in the Font dialog box, change the font to Helvetica
Bold, 16-point type. Click OK.
You can change the
font of the label using
the Font property in
the Object Inspector.
Click on the ellipsis to
display a standard
font dialog.
4 Position the label in the upper right corner.
5 From the Additional Component palette page, drop a TImage component next to
the label (named Image1 by default).
6 To add an image to the Image1 component, click the Picture property. Click the ellipsis to display the Picture editor.
7 In the Picture editor, choose Load and navigate to earth.ico. On C++Builder, its
path is Program Files\Common Files\Borland Shared\images\icons\earth.ico.
8 Double-click earth.ico. Click OK to load the picture and to close the Picture editor.
9 Size the default image area to the size of the picture. Place the image next to the
label.
You can drag the edge to
set the width of Image, or
you can set its Width
property in the Object
Inspector.
10 To align the text and the image, select both objects on the form, right-click, and
choose Align. In the Alignment dialog box, under Vertical, click Bottoms.
11 Choose File|Save All to save the project.
12 Press F9 to compile and run your application.
Close the application when you’re ready to continue.
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Q u i c k S t a r t
W r i t i n g a n e v e n t h a n d l e r
Writing an event handler
Most components on the Component palette have events, and most components
have a default event. A common default event is OnClick, which gets called whenever
a component, such as TButton, is clicked. If you select a component on a form and
click the Object Inspector’s Events tab, you’ll see a list of the component’s events.
For more information about events and event handlers, see “Developing the
application user interface” in the Developer’s Guide or online Help.
Writing the Update Now! command event handler
First, you’ll write the event handler for the Update Now! command and button:
1 Double-click the ActionList component to display the Action List editor.
2 Select (No Category) to see Action1 and Action2.
3 Double-click Action1. In the Code editor, the following skeleton event handler
appears:
void __fastcall TForm1::Action1Execute(TObject *Sender)
{
}
Right where the cursor is positioned (between the braces), type:
if(ClientDataSet1->State == dsEdit || ClientDataSet1->State == dsInsert)
ClientDataSet1->Post();
ClientDataSet1->ApplyUpdates(-1);
This event handler first checks to see what state the database is in. When you move
off a changed record, it is automatically posted. But if you don’t move off a changed
record, the database remains in edit or insert mode. The if statement posts any data
that may have been changed but was not passed to the client dataset. The next
statement applies updates held in the client dataset to the database.
Note
Changes to the data are not automatically posted to the database when using
dbExpress. You need to call the ApplyUpdates method to write all updated, inserted,
and deleted records from the client dataset to the database.
Writing the Exit command event handler
Next, we’ll write the event handler for the Exit command:
1 Double-click the ActionList component to display the Action List editor if it is not already displayed.
2 Click (No Category) so you see Action2.
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3 Double-click Action2. The Code editor displays the following skeleton event
handler:
void __fastcall TForm1::Action2Execute(TObject *Sender)
{
}
Right where the cursor is positioned (between the braces), type:
Close();
This event handler will close the application when the File|Exit command on the
menu is used.
4 Close the Action List editor.
5 Choose File|Save All to save the project.
Writing the FormClose event handler
Finally, you’ll write another event handler that is invoked when the application is
closed. The application can be closed either by using File|Exit or by clicking the X in