delphi 文本框内容空白时加上提示文字,输入内容时提示文字不显示 ...

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原作者: [db:作者] 来自: [db:来源] 收藏邀请

需求：
当文本框没有输入内容且输入焦点不在文本框时，显示提示文字：“请输入帐号”

当文本框得到输入焦点时提示文字不显示

实现的思路有两种，

一种是在外部控制，在文本框的OnEnter事件中，将提示文字清除，在OnExit事件中如果文本框的Text为空时给文本框加上提示文字，

而且提示文字的颜色和正常文字的颜色有区别，一般大家使用灰色

另一种是重新制作一个控件，当文本框获取焦点且Text为空时，使用WM_PAINT消息，在其中绘制提示文字

ifNot Focused and (Text='') and (HelpText<>'') then

begin

//绘制提示文字

end;

加入提示文字和提示文字的字体设置这两个属性

//提示性文字字体颜色

property HelpTextFont:TFont read FHelpTextFont write SetHelpTextFont;

//提示性文字

propertyHelpText:WideString read FHelpText write SetHelpText;

我使用自定义控件的方式来实现，重用性比较高

下面贴出这个控件的全部代码:

unit SkinHintEdit;  

interface  

uses  
  Windows,Classes,Controls,SysUtils,Messages,StdCtrls,Forms,  
  Graphics;  

const  
  //提示文字颜色  
  CONST_DEF_HELPTEXT_FONTCOLOR=clGray;  
  CONST_DEF_HELPTEXT_FONTNAME='Tahoma';  
  CONST_DEF_HELPTEXT_FONTSIZE=9;  
  CONST_DEF_HELPTEXT_FONTSTYLE=[];  

type  
  TSkinHintEdit=class(TCustomEdit)  
private  
    FHelpText: WideString;  
    FHelpTextFont: TFont;  
procedure SetHelpText(const Value: WideString);  
procedure SetHelpTextFont(const Value: TFont);  
protected  
procedure WMPaint(var Message:TMessage);message WM_PAINT;  
public  
constructor Create(AOwner:TComponent);override;  
destructor Destroy;override;  
published  
    ///////////////自定义扩展属性/////////////////  
    //指导性文字字体颜色  
property HelpTextFont:TFont read FHelpTextFont write SetHelpTextFont;  
    //指导性文字  
property HelpText:WideString read FHelpText write SetHelpText;  
    ///////////////默认文本框自带属性////////////  
property Align;  
property Alignment;  
property Anchors;  
property AutoSelect;  
property AutoSize;  
property BevelEdges;  
property BevelInner;  
property BevelKind default bkNone;  
property BevelOuter;  
property BevelWidth;  
property BiDiMode;  
property BorderStyle;  
property CharCase;  
property Color;  
property Constraints;  
property Ctl3D;  
property DoubleBuffered;  
property DragCursor;  
property DragKind;  
property DragMode;  
property Enabled;  
property Font;  
property HideSelection;  
property ImeMode;  
property ImeName;  
property MaxLength;  
property NumbersOnly;  
property OEMConvert;  
property ParentBiDiMode;  
property ParentColor;  
property ParentCtl3D;  
property ParentDoubleBuffered;  
property ParentFont;  
property ParentShowHint;  
property PasswordChar;  
property PopupMenu;  
property ReadOnly;  
property ShowHint;  
property TabOrder;  
property TabStop;  
property Text;  
property TextHint;  
property Touch;  
property Visible;  
property OnChange;  
property OnClick;  
property OnContextPopup;  
property OnDblClick;  
property OnDragDrop;  
property OnDragOver;  
property OnEndDock;  
property OnEndDrag;  
property OnEnter;  
property OnExit;  
property OnGesture;  
property OnKeyDown;  
property OnKeyPress;  
property OnKeyUp;  
property OnMouseActivate;  
property OnMouseDown;  
property OnMouseEnter;  
property OnMouseLeave;  
property OnMouseMove;  
property OnMouseUp;  
property OnStartDock;  
property OnStartDrag;  
end;  



procedure Register;  

implementation  

procedure Register;  
begin  
  RegisterComponents('SkinEngine',[TSkinHintEdit]);  
end;  


{ TSkinHintEdit }  


constructor TSkinHintEdit.Create(AOwner: TComponent);  
begin  
  FHelpText:='';  
  //提示文字颜色  
  FHelpTextFont:=TFont.Create;  
  FHelpTextFont.Color:=CONST_DEF_HELPTEXT_FONTCOLOR;  
  FHelpTextFont.Name:=CONST_DEF_HELPTEXT_FONTNAME;  
  FHelpTextFont.Size:=CONST_DEF_HELPTEXT_FONTSIZE;  
  FHelpTextFont.Style:=CONST_DEF_HELPTEXT_FONTSTYLE;  
inherited Create(AOwner);  
end;  



destructor TSkinHintEdit.Destroy;  
begin  
  FreeAndNil(FHelpTextFont);  
inherited;  
end;  


procedure TSkinHintEdit.SetHelpText(const Value: WideString);  
begin  
  FHelpText := Value;  
end;  

procedure TSkinHintEdit.SetHelpTextFont(const Value: TFont);  
begin  
  FHelpTextFont.Assign(Value);  
  Invalidate;  
end;  


procedure TSkinHintEdit.WMPaint(var Message: TMessage);  
var  
  ClientDC:HDC;  
  ClientCanvas:TCanvas;  
  HelpTextDrawLeft,  
  HelpTextDrawTop:Integer;  
begin  
  Inherited;  
if Not Focused and (Text='') and (HelpText<>'') then  
begin  
    ClientDC:=GetDC(Handle);  
    Try  
      ClientCanvas:=TCanvas.Create;  
      ClientCanvas.Handle:=ClientDC;  
      ClientCanvas.Font.Assign(FHelpTextFont);  
      HelpTextDrawLeft:=0;  
      HelpTextDrawTop:=(Height-ClientCanvas.TextHeight(FHelpText) ) div 2-2;  
      ClientCanvas.TextOut(HelpTextDrawLeft,HelpTextDrawTop,FHelpText);  
    Finally  
      ReleaseDC(Handle,ClientDC);  
      ClientCanvas.Free;  
    End;  
end;  
end;  


end.