delphi - 如何自定义绘制 TEdit 控件文本？

Question

我想使用与默认不同的 Font.Color 绘制一段 TEdit.Text。有没有例子如何做到这一点？

我正在尝试做这样的事情:

_{注意:这张截图只是一个毛茸茸的草稿，但它让我相信什么问题是可以解决的。}

Answer 1

Edit 控件不支持所有者绘制，但您可以通过子类化它并处理来自定义绘制它>WM_PAINT(以及许多其他消息)。这是可行的，但实际 100% 正确实现将是一个痛苦的世界。来自文档:Developing Custom Draw Controls in Visual C++ :

Note that owner-draw will work for most controls. However, it doesn't work for edit controls; and with regards to the list control, it works only for report-view style

我也很想知道兔子洞到底有多深，所以，
这是使用插入器类的代码示例(仍然需要实现选择，但当插入符位于控件中时自定义绘图可以工作):

type
  TEdit = class(StdCtrls.TEdit)
  private
    FCanvas: TCanvas;
    procedure WMPaint(var Message: TWMPaint); message WM_PAINT;
  protected
    procedure WndProc(var Message: TMessage); override;
    procedure Paint; virtual;
    procedure PaintWindow(DC: HDC); override;
    property Canvas: TCanvas read FCanvas;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  end;

...

constructor TEdit.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FCanvas := TControlCanvas.Create;
  TControlCanvas(FCanvas).Control := Self;
end;

destructor TEdit.Destroy;
begin
  FCanvas.Free;
  inherited Destroy;
end;

procedure TEdit.Paint;
var
  R: TRect;
  I: Integer;
  S: String;
begin
  R := ClientRect;
  Inc(R.Left, 1);
  Inc(R.Top, 1);
  Canvas.Brush.Assign(Self.Brush);
  Canvas.Font.Assign(Self.Font);
  for I := 1 to Length(Text) do
  begin
    if Text[I] in ['0'..'9'] then
      Canvas.Font.Color := clRed
    else
      Canvas.Font.Color := clGreen;
    S := Text[I];
    DrawText(Canvas.Handle, PChar(S), -1, R, DT_LEFT or DT_NOPREFIX or
      DT_WORDBREAK or DrawTextBiDiModeFlagsReadingOnly);
    Inc(R.Left,Canvas.TextWidth(S));
  end;
end;

procedure TEdit.PaintWindow(DC: HDC);
begin
  FCanvas.Lock;
  try
    FCanvas.Handle := DC;
    try
      TControlCanvas(FCanvas).UpdateTextFlags;
      Paint;
    finally
      FCanvas.Handle := 0;
    end;
  finally
    FCanvas.Unlock;
  end;
end;

procedure TEdit.WMPaint(var Message: TWMPaint);
begin
  ControlState := ControlState+[csCustomPaint];
  inherited;
  ControlState := ControlState-[csCustomPaint];
end;

procedure TEdit.WndProc(var Message: TMessage);
begin
  inherited WndProc(Message);
  with Message do
    case Msg of
      CM_MOUSEENTER, CM_MOUSELEAVE, WM_LBUTTONUP, WM_LBUTTONDOWN,
      WM_KEYDOWN, WM_KEYUP,
      WM_SETFOCUS, WM_KILLFOCUS,
      CM_FONTCHANGED, CM_TEXTCHANGED:
      begin
        Invalidate;
      end;
   end; 
end;