size="3"> </font><font face="Arial" size="3">}</p>
<p>else raise; { </font><font face="宋體" lang="ZH-CN" size="3">否</font><font size="3">
</font><font face="宋體" lang="ZH-CN" size="3">則</font><font size="3"> </font><font
face="Arial" size="3">}</p>
<p>end;</p>
<p>end;</font><font face="宋體" lang="ZH-CN" size="3"></p>
<p>　</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>19.3 Delphi</font><font face="宋體" lang="ZH-CN" size="3">部件編程實(shí)例</font><font
size="3"> </font><font face="Arial" size="3"></p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>19.3.1 </font><font face="宋體" lang="ZH-CN" size="3">創(chuàng)建數(shù)據(jù)庫相關(guān)的日歷控制－</font><font
face="Arial" size="3">TDBCalendar</p>
<p></font><font face="宋體" lang="ZH-CN" size="3">　</p>
<p>　　當(dāng)處理數(shù)據(jù)庫聯(lián)接時(shí)，將控制和數(shù)據(jù)直接相聯(lián)是很重要的。就是說，應(yīng)用程序可以建立控制與數(shù)據(jù)庫之間的鏈。</font><font
face="Arial" size="3">Delphi</font><font face="宋體" lang="ZH-CN" size="3">包括了數(shù)據(jù)相關(guān)的標(biāo)簽、編輯框、列表框和柵格。用戶可以使自己的控制與數(shù)據(jù)相關(guān)。</p>
<p>　　數(shù)據(jù)相關(guān)有若干等級(jí)。最簡(jiǎn)單的是只讀數(shù)據(jù)相關(guān)或數(shù)據(jù)瀏覽，以及反映數(shù)據(jù)庫當(dāng)前狀態(tài)的能力。比較復(fù)雜的是數(shù)據(jù)相關(guān)的編輯，也即用戶可以在控制上操作數(shù)據(jù)庫中的數(shù)據(jù)。</p>
<p>　　在本部分中將示例最簡(jiǎn)單的情況，即創(chuàng)建聯(lián)接數(shù)據(jù)庫的單個(gè)字段的只讀控制。本例中將使用</font><font
face="Arial" size="3">Component Palette</font><font face="宋體" lang="ZH-CN" size="3">的</font><font
face="Arial" size="3">Samples</font><font face="宋體" lang="ZH-CN" size="3">頁中的</font><font
face="Arial" size="3">TCalendar</font><font face="宋體" lang="ZH-CN" size="3">部件。</font><font
face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">創(chuàng)建數(shù)據(jù)相關(guān)的日歷控制包括下列幾步：</font><font
face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">●</font><font size="3"> </font><font
face="宋體" lang="ZH-CN" size="3">創(chuàng)建和注冊(cè)部件</font><font face="Arial"
size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">●</font><font size="3"> </font><font
face="宋體" lang="ZH-CN" size="3">使控制只讀</font><font face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">●</font><font size="3"> </font><font
face="宋體" lang="ZH-CN" size="3">增加數(shù)據(jù)聯(lián)接</font><font face="Arial" size="3">(Data
Link)</p>
<p></font><font face="宋體" lang="ZH-CN" size="3">●</font><font size="3"> </font><font
face="宋體" lang="ZH-CN" size="3">響應(yīng)數(shù)據(jù)改變</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>19.3.1. 1</font><font face="宋體" lang="ZH-CN" size="3">創(chuàng)建和注冊(cè)部件</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">每個(gè)部件的創(chuàng)建都從相同的方式開始，在本例中將遵循下列過程：</font><font
face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">●</font><font size="3"> </font><font
face="宋體" lang="ZH-CN" size="3">將部件庫單元命名為</font><font face="Arial"
size="3">DBCal</p>
<p></font><font face="宋體" lang="ZH-CN" size="3">●</font><font size="3"> </font><font
face="宋體" lang="ZH-CN" size="3">從</font><font face="Arial" size="3">TCalendar</font><font
face="宋體" lang="ZH-CN" size="3">繼承一個(gè)新部件，名為</font><font
face="Arial" size="3">TDBCalendar</p>
<p></font><font face="宋體" lang="ZH-CN" size="3">●</font><font size="3"> </font><font
face="宋體" lang="ZH-CN" size="3">在</font><font face="Arial" size="3">Component
Palette</font><font face="宋體" lang="ZH-CN" size="3">的</font><font face="Arial"
size="3">Samples</font><font face="宋體" lang="ZH-CN" size="3">頁中注冊(cè)</font><font
face="Arial" size="3">TDBCalendar</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">下面就是創(chuàng)建的代碼：</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>unit DBCal;</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>interface</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>uses SysUtils, WinTypes, WinProc, Messages, Classes, Graphics, Controls, </p>
<p>Forms, Grids, Calendar;</p>
<p>type</p>
<p>TDBCalendar=class(TCalendar)</p>
<p>end;</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>procedure Register;</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>implementation</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>procedure Register;</p>
<p>begin</p>
<p>RegisterComponents(Samples</font><font face="宋體" lang="ZH-CN" size="3">，</font><font
face="Arial" size="3">[TDBabendar]);</p>
<p>end;</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>end.</font><font face="宋體" lang="ZH-CN" size="3"></p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>19.3.1.2 </font><font face="宋體" lang="ZH-CN" size="3">使控制只讀</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">因?yàn)檫@個(gè)數(shù)據(jù)日歷以只讀方式響應(yīng)數(shù)據(jù)，所以用戶不能在控制中改變數(shù)據(jù)并指望它們反映到數(shù)據(jù)庫中。</font><font
face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">使日歷只讀包含下列兩步：</font><font
face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">●</font><font size="3"> </font><font
face="宋體" lang="ZH-CN" size="3">增加只讀屬性</font><font face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">●</font><font size="3"> </font><font
face="宋體" lang="ZH-CN" size="3">允許所需的更新</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>1. </font><font face="宋體" lang="ZH-CN" size="3">增加只讀屬性</font><font
face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">給日歷控制增加只讀選項(xiàng)是直接過程。通過增加屬性，可以提供在設(shè)計(jì)時(shí)使控制只讀的方法，當(dāng)屬性值被設(shè)為</font><font
face="Arial" size="3">True</font><font face="宋體" lang="ZH-CN" size="3">，將使控制中所有元素不可被選。</font><font
face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">⑴</font><font size="3"> </font><font
face="宋體" lang="ZH-CN" size="3">增加屬性聲明和保存值的</font><font
face="Arial" size="3">private</font><font face="宋體" lang="ZH-CN" size="3">域：</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>type</p>
<p>TDBCalendar=class(TClendar)</p>
<p>private</p>
<p>FReadOnly: Boolean;</p>
<p>public</p>
<p>constructor Create (Aowner: TComponent); override;</p>
<p>published</p>
<p>property ReadOnly: Boolean read FReadOnly write FReadOnly default True;</p>
<p>end;</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>constructor TDBCalendar.Create(Aowner: TComponent);</p>
<p>begin</p>
<p>inherited Create(AOwner);</p>
<p>FReadOnly := True;</p>
<p>end;</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">⑵</font><font size="3"> </font><font
face="宋體" lang="ZH-CN" size="3">覆蓋</font><font face="Arial" size="3">SelectCell</font><font
face="宋體" lang="ZH-CN" size="3">方法，使得當(dāng)控制是只讀時(shí)，不允許選擇：</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>function TDBCalendar.SelectCell(ACol, Arow: Longint): Boolean;</p>
<p>begin</p>
<p>if FReadOnly then </p>
<p>Result := False</p>
<p>else </p>
<p>Result := inherited SelectCell(Acol</font><font face="宋體" lang="ZH-CN" size="3">，</font><font
face="Arial" size="3">ARow);</p>
<p>end;</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">還要在</font><font face="Arial"
size="3">TDBcalendar</font><font face="宋體" lang="ZH-CN" size="3">的聲明中聲明</font><font
face="Arial" size="3">SelectCell</font><font face="宋體" lang="ZH-CN" size="3">。</font><font
face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">如果現(xiàn)在將</font><font
face="Arial" size="3">Calendar</font><font face="宋體" lang="ZH-CN" size="3">加入窗體，會(huì)發(fā)現(xiàn)部件完全忽略鼠標(biāo)和擊鍵事件，而且當(dāng)改變?nèi)掌跁r(shí)，也不能改變選擇的位置。下面將使控制響應(yīng)更新。</font><font
face="Arial" size="3"></p>
<p>2. </font><font face="宋體" lang="ZH-CN" size="3">允許所需的更新</font><font
face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">只讀日歷使用</font><font
face="Arial" size="3">SelectCell</font><font face="宋體" lang="ZH-CN" size="3">方法實(shí)現(xiàn)各種改變，包括設(shè)置</font><font
face="Arial" size="3">Row</font><font face="宋體" lang="ZH-CN" size="3">和</font><font
face="Arial" size="3">Col</font><font face="宋體" lang="ZH-CN" size="3">的值。當(dāng)日期改變時(shí)，</font><font
face="Arial" size="3">UpdateCalendar</font><font face="宋體" lang="ZH-CN" size="3">方法設(shè)置</font><font
face="Arial" size="3">Row</font><font face="宋體" lang="ZH-CN" size="3">和</font><font
face="Arial" size="3">Col</font><font face="宋體" lang="ZH-CN" size="3">的值，但因?yàn)?lt;/font><font
face="Arial" size="3">SelectCell</font><font face="宋體" lang="ZH-CN" size="3">不允許你改變，即使日期改變了，選擇仍留在原處。</font><font
face="Arial" size="3"></p>
<p></font><font face="宋體" lang="ZH-CN" size="3">可以給日歷增加一個(gè)</font><font
face="Arial" size="3">Boolean</font><font face="宋體" lang="ZH-CN" size="3">標(biāo)志，當(dāng)標(biāo)志為</font><font
face="Arial" size="3">True</font><font face="宋體" lang="ZH-CN" size="3">時(shí)允許改變：</p>
<p></font><font size="3">　</font><font face="Arial" size="3"></p>
<p>type</p>
<p>TDBCalendar=class(TCalendar)</p>
<p>private</p>
<p>Fupdating: Boolean;</p>
<p>protected</p>
<p>function SelectCell(Acol, Arow: Longint); Boolean; override;</p>
<p>public</p>
<p>procedure Update