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cellspacing="1" cellpadding="1" bgcolor="#000000"><tr bgcolor="#FFFFFF"><td width="100%" colspan="4" align="left"><table width="95%" align="center"><tr><td class="font1"><p align="center"><br><font size="3">制作用于日期时间型字段的DELPHI数据感知控件</font><br><span class="nava"><font color="#CC9933">2000-06-25· -·中国计算机世界出版服务公司</font></span></p><p> 用DELPHI开发C/S应用方便而快速，因为它拥有大量易于使用的数据访问和数据感知控件。然而万事总是难以完美，DELPHI的DBEdit控件用于输入日期时间型字段却很不方便，为了改善这一缺点，笔者开发了一个DBDateTime数据感知控件，大大方便了时间和日期的输入。</p> <p> 创建一个构件时，最重要的一步是选择正确的父类，这样可以减少代码的编写。DELPHI的构件库中已有一个TDateTimePicker构件，可以以下拉日历或利用SpinButton递增、递减的方式方便地输入和改变日期、时间，但它没有数据感知的能力。因此，我们可以以它为父类，派生出一个新的控件，加上能与数据集通信的数据感知功能。</p> <p> 数据感知控件通过DataLink对象与DataSource进行交互，所以为控件增加数据感知能力需要创建一个TDataLink（或其派生类）对象作为控件的成员，并为控件创建公开的DataField和DataSource属性；然后需响应TDataLink对象的OnDataChange和OnUpdateData事件。下面是控件的主要源代码，并带有相应的注释：</p> <blockquote> <blockquote> <p> {定义从TDateTimePicker派生的TDBDateTime类。注意，在单元接口的Uses中应加入DB，DBCTRLS引用}type<br> TDBDateTime=class(TDateTimePicker)<br> private<br> FDataLink:TFieldDataLink;<br> //TFieldDataLink是TDataLink的派生类，处理单个字段与DataSource的交互<br> procedureDataChange(sender:Tobject);<big><br> </big>//当DataSet的记录改变（如浏览记录）时触发OnDataChange事件，DataChange将作为该事件的事件处理句柄<br> procedureUpdateData(sender:Tobject);<br> //更新DataSet前触发OnUpdateData事件，UpdateData将作为该事件的事件处理句柄<br> functionGetDataSource:TDataSource;<br> procedureSetdataSource(value:TDataSource);<br> FunctionGetDataField:String;<br> procedureSetdataField(Value:String);<br> procedureCMexit(varMessage:TCMExit);message CM_EXIT;//当控件失去焦点时触发CM_EXIT消息<br> protected<br> procedureChange;override;//控件中日期、时间改变时触发OnChange事件<br> procedureNotification(AComponent:TComponent;<br> Operation:Toperation);override;<br> //当某一控件从FORM上移走时DELPHI的IDE调用该方法通知其它控件<br> public<br> constructorCreate(AOwner:Tcomponent);override;<br> destructorDestroy;override;<br> published<br> propertyDataSource:TDataSourcereadGetDataSource<br> writeSetDataSource;//为控件增加DataSource属性，使它能与DataSource构件连接<br> propertyDataField:StringreadGetDataField<br> writeSetDataField;<br> end;//为控件增加DataField属性，<br> 使它指向代表某一字段的TField对象<br> <br> procedureRegister;//注册构件<br> <br> implementation<br> <br> procedureTDBDateTime.CMExit;<br> begin<br> try<br> FDataLink.UpdateRecord;<br> //控件失去焦点时更新DataSet，这将触发OnUpdateData事件<br> except<br> Setfocus;<br> raise;<br> end;<br> DoExit;<br> end;<br> <br> constructorTDBDateTime.Create(Aowner:Tcomponent);<br> begin<br> inheritedCreate(Aowner);<br> //创建DataLink对象，挂接OnDataChange、<br> OnUpdateData事件处理句柄<br> FDataLink:=TFieldDataLInk.Create;<br> FDataLink.OnDataChange:=DataChange;<br> FDataLink.OnUpdateData:=Updatedata;<br> end;<br> <br> DestructorTDBDateTime.Destroy;<br> begin<br> FDataLink.OnDataChange:=nil;<br> FDataLink.OnUpdateData:=nil;<br> FDataLink.Free;<br> inheritedDestroy;<br> end;<br> <br> functionTDBDateTime.GetdataSource:TdataSource;<br> begin<br> result:=FDataLink.DataSource;<br>⌨️ 快捷键说明
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