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

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.