具有自定义位置的 TTrackBar？

Question

我正在尝试在 Win 7 缩放轨迹栏中复制 PAINT 应用程序的行为： （我知道这是一个常见的轨迹栏控件）

100% 位于中心。 它有 11 个可用位置：

等等……

12.5%, 25%, 50%, 100%, 200%, 300%, 400%, 500%, 600%, 700%, 800%

所以我的缩放值 (ZoomArray) 是：
0.125, 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7, 8

这很容易，我可以将 Min 设置为 1 并将 Max 设置为 11 并获得我需要的值：
ZoomArray[TrackBar1.Position]

问题是如何保持 100% 在中心，而唯一可用的位置是上面那个？

我尝试在数组中使用虚拟值来将 1 保持在中心，例如：
0.125, 0.25, 0.5, -1, -1, -1, -1, 1, 2, 3, 4, 5, 6, 7, 8
并在更改事件上重新定位轨迹栏，但我的逻辑似乎无法正常工作。

有什么想法吗？

Answer 1

这是一种从TTrackbar 派生新控件的替代方法，它移除了自动抽动并处理滚动消息中的滑动，其行为几乎与 Paint 中的控件相同。用D2007编译，试着评论一下：

unit Unit1;

interface

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

type
  TCNHScroll = TWMHScroll;

  TTrackBar = class(comctrls.TTrackBar)  // interposer class for quick test
  protected
    procedure CreateParams(var Params: TCreateParams); override;
    procedure CreateWnd; override;
    procedure CNHScroll(var Message: TCNHScroll); message CN_HSCROLL;
  public
    constructor Create(AOwner: TComponent); override;
  end;

  TForm1 = class(TForm)
    Label1: TLabel;
    TrackBar1: TTrackBar;
    procedure TrackBar1Change(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

uses
  commctrl;

{$R *.dfm}

procedure TForm1.TrackBar1Change(Sender: TObject);
begin
  // account for non-linear scaling for a sensible value
  if TrackBar1.Position <= 8 then
    Label1.Caption := IntToStr(TrackBar1.Position * 125)
  else
    Label1.Caption := IntToStr(TrackBar1.Position * 1000 - 7000)
end;

{ TTrackBar }

constructor TTrackBar.Create(AOwner: TComponent);
begin
  inherited;

  // We'll have 15 positions which should account for the following values 
  // 125 250 - 500 - - - 1000 2000 3000 4000 5000 6000 7000 8000
  // positions 3, 5..7 will be skipped when tracking
  Min := 1;
  Max := 15;
  LineSize := 1;
  PageSize := 1;
end;

procedure TTrackBar.CreateParams(var Params: TCreateParams);
begin
  inherited;
  // remove automatic ticks so that we don't have ticks at 3 and 5..7
  Params.Style := Params.Style and not TBS_AUTOTICKS;
end;

procedure TTrackBar.CreateWnd;
begin
  inherited;
  // first and last tick not required
  SetTick(2);  //  250
  SetTick(4);  //  500
  SetTick(8);  // 1000
  SetTick(9);  // 2000
  SetTick(10); 
  SetTick(11);
  SetTick(12);
  SetTick(13);
  SetTick(14); // 7000
end;

procedure TTrackBar.CNHscroll(var Message: TCNHScroll);
var
  Pos: Integer;
begin
  // prevent jumping back and forth while thumb tracking, do not slide to the
  // next tick until a threshold is passed
  if Message.ScrollCode = SB_THUMBTRACK then begin
    case Message.Pos of            
      5: SendMessage(Handle, TBM_SETPOS, 1, 4);
      6, 7: SendMessage(Handle, TBM_SETPOS, 1, 8);
    end;
  end;

  // for line and page and rest of the scrolling, skip certain ticks
  Pos := SendMessage(Handle, TBM_GETPOS, 0, 0);
  if Pos > Position then      // compare with previous position
    case Pos of
      3: SendMessage(Handle, TBM_SETPOS, 1, 4);
      5..7: SendMessage(Handle, TBM_SETPOS, 1, 8);
    end;
  if Pos < Position then
    case Pos of
      3: SendMessage(Handle, TBM_SETPOS, 1, 2);
      5..7: SendMessage(Handle, TBM_SETPOS, 1, 4);
    end;

  inherited;
end;

end.

如果需要，垂直实施将是类似的。这并不是真正的成品，只是模拟上述控件行为的试验。

Answer 2

将TrackBar.Max 设置为14，并实现OnChange 和OnKeyDown 处理程序，以及一些用于放大和缩小的按钮OnClick 处理程序。此外，设置 TrackBar.PageSize = 4 以使 PageUp 和 PageDown 键正常工作。

const
  ZoomTickCount = 15;

function ZoomLevelPos(Position: Integer; GoneUp: Boolean): Integer;
const
  Ticks: array[0..ZoomTickCount - 1] of Integer =
    (0, 1, 1, 2, 2, 2, 2, 9, 10, 11, 12, 13, 14, 15, 16);
begin
  Result := Position;
  if GoneUp then
    while (Result < High(Ticks)) and (Ticks[Result] = Ticks[Position - 1]) do
      Inc(Result)
  else
    while (Result > Low(Ticks)) and (Ticks[Result - 1] = Ticks[Position]) do
      Dec(Result);
end;

procedure TForm1.ZoomTrackBarChange(Sender: TObject);
const
  Zooms: array[0..ZoomTickCount - 1] of Single =
    (0.125, 0.25, 0.25, 0.5, 0.5, 0.5, 0.5, 1, 2, 3, 4, 5, 6, 7, 8);
begin
  ZoomTrackBar.Position := ZoomLevelPos(ZoomTrackBar.Position, False);
  Label1.Caption := Format('%.1n%%', [Zooms[ZoomTrackBar.Position] * 100]);
end;

procedure TForm1.ZoomTrackBarKeyDown(Sender: TObject; var Key: Word;
  Shift: TShiftState);
begin
  if Key in [VK_DOWN, VK_RIGHT] then
  begin
    ZoomTrackBar.Position := ZoomLevelPos(ZoomTrackBar.Position + 1, True);
    Key := 0;
  end;
end;

procedure TForm1.ZoomInButtonClick(Sender: TObject);
begin
  ZoomTrackBar.Position := ZoomLevelPos(ZoomTrackBar.Position + 1, True);
end;

procedure TForm1.ZoomOutButtonClick(Sender: TObject);
begin
  ZoomTrackBar.Position := ZoomTrackBar.Position - 1;
end;