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align="center"><tr><td colspan="3" valign="top" width="75%"><table width="98%" border="0" 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">改变VCL的行为--一个使用可视化元件的实例</font><br><span class="nava"><font color="#CC9933">2000-10-08· 周健·delphi技术网</font></span></p> 要使一个可视化控件的行为与其默认行为不同，我们通常要从这个原始类继承，创建一个新的控件。本文将介绍如何在不创建新类的情况下动态改变原生Delphi可视化控件的行为。<br> 这可能实现吗？秘密在于在控件之前抢先截获Windows消息。这可以通过使用一个叫做WindowProc的TControl属性来实现，这个属性实质上指向控件的Windows消息事件处理器（event handler）。<br> 为了展示这一技术，我们将创建一个LinkedLabel控件，可以将它连接到任何TControl控件并且动态改变它的行为。TLinkedLabel由TLabel继承而来，附加4个公开的属性：<br> Associate —— 将被改变行为的相连控件<br> CapsLock —— 当这个Boolean属性被设置为True时，特定类型的控件将把小写键盘输入作为大写来处理。这个属性并不对所有控件有效，因为并不是所有的控件都以相同的方式相应WM_CHAR消息。经测试Edit，MaskEdit，Memo，和RichEdit控件都对CapsLock属性有响应，但是ComboBox则不响应。很明显，CapsLock属性对于很多其他控件（如Button、CheckBox等）只有很小的影响，或者没有影响。<br> Gap —— LinkedLabel与相连控件的距离<br> OnTop —— 这个Boolean属性决定LinkedLabel出现在相连控件的左侧还是顶端。<br> 另外，TlinkedLabel将保持自身和相连控件的Enabled和Visible属性相一致。它也会保持自身和相连控件的距离和角度，也就是说，当你移动LinkedLabel时，其关联也会随之移动，反之亦然。<br>我们来看一下TLinkedLabel类的声明，如图1所示。<br>unit LinkedLabel; <br> <br>interface<br> <br>uses<br> Messages, Classes, Controls, StdCtrls; <br> <br>type<br> TLinkedLabel = class(TLabel) <br> private<br> // 相连控件. <br> FAssociate: TControl; <br> // 将 FAssociate 置为全大写模式<br> FCapsLock: Boolean; <br> // 标签与关联控件之间的距离 <br> FGap: Integer; <br> // 标签在关联控件顶端时为true <br> FOnTop: Boolean; <br> // 保存 FAssociate.WindowProc的原始值<br> FOldWinProc: TWndMethod; <br> // 用于防止无限更新循环<br> FUpdating: Boolean; <br> protected<br> procedure Adjust(MoveLabel: Boolean); <br> procedure SetGap(Value: Integer); <br> procedure SetOnTop(Value: Boolean); <br> procedure SetAssociate(Value: TControl); <br> procedure NewWinProc(var Message: TMessage); <br> procedure Notification(AComponent: TComponent; <br> Operation: TOperation); override;<br> procedure WndProc(var Message: TMessage); override;<br> <br>public<br> constructor Create(AOwner :TComponent); override;<br> destructor Destroy; override;<br> published<br> property Associate: TControl<br> read FAssociate write SetAssociate; <br> property CapsLock: Boolean<br> read FCapsLock write FCapsLock; <br> property Gap: Integer read FGap write SetGap default 8; <br> property OnTop: Boolean read FOnTop write SetOnTop; <br> end;<br><br> 现在让我们来仔细看看这个控件中的不同方法，先由构造器（constructor）开始。首先说明一下，当创建一个新对象时，与它相关联的所有内存都被清空。这个动作将会自动把Fassociate和FoldWinProc设置为nil，将FcapsLock、FonTop、Fupdating设置为False。所有这些都不需要在构造器中明确的初始化它们。因此，唯一需要我们在构造器中设置的就是Gap的默认值。<br>implementation<br> <br>constructor TLinkedLabel.Create(AOwner: TComponent); <br>begin<br>⌨️ 快捷键说明
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