為什么FMXTScrollBarOnMouseUp不起作用？-有解無憂

我有一個滾動條，滑鼠事件分配給 onChange、onMouseWheel 和 onm ouseUp。onChange 和 wheel 事件作業正常，但 onm ouseUp 事件不會觸發。在除錯時深入到 TControl 方法，我注意到事件變數 (FOnMouseUp) 為零。事件是在IDE中分配的，我把它放在表單的onCreate事件中，另外我在創建表單后嘗試在其他各個地方分配它，但無濟于事。是什么賦予了？

這是一個簡單的可重現示例，其中所有三個滾動條滑鼠事件都不會觸發：

 `TForm4 = class(TForm)
    ScrollBar1: TScrollBar;
    Label1: TLabel;
    procedure ScrollBar1MouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Single);
    procedure ScrollBar1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Single);
    procedure ScrollBar1MouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Single);
    procedure ScrollBar1Change(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form4: TForm4;

implementation

{$R *.fmx}

procedure TForm4.ScrollBar1Change(Sender: TObject);
begin
  Label1.Text := 'onChange: '   Screen.MousePos.Y.ToString;
end;

procedure TForm4.ScrollBar1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Single);
begin
  Label1.Text := 'mousedown: '   Y.ToString;
end;

procedure TForm4.ScrollBar1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Single);
begin
  Label1.Text := 'mousemove: '   Y.ToString;
end;

procedure TForm4.ScrollBar1MouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Single);
begin
  Label1.Text := 'mouseUP: '   Y.ToString;
end;

end.`

和 .FMX：

`object Form4: TForm4
  Left = 0
  Top = 0
  Caption = 'Form4'
  ClientHeight = 480
  ClientWidth = 640
  FormFactor.Width = 320
  FormFactor.Height = 480
  FormFactor.Devices = [Desktop]
  DesignerMasterStyle = 0
  object ScrollBar1: TScrollBar
    SmallChange = 0.000000000000000000
    Orientation = Vertical
    Position.X = 616.000000000000000000
    Position.Y = 8.000000000000000000
    Size.Width = 18.000000000000000000
    Size.Height = 449.000000000000000000
    Size.PlatformDefault = False
    TabOrder = 0
    OnChange = ScrollBar1Change
    onm ouseDown = ScrollBar1MouseDown
    onm ouseMove = ScrollBar1MouseMove
    onm ouseUp = ScrollBar1MouseUp
  end
  object Label1: TLabel
    Position.X = 568.000000000000000000
    Position.Y = 152.000000000000000000
    Text = 'Label1'
    TabOrder = 1
  end
end`

uj5u.com熱心網友回復：

原因是滾動條包含子物件，例如軌道、拇指和最小和最大按鈕。回應滑鼠事件的是這些物件，而不是父物件。所以解決方案是將滑鼠事件設定為這些物件。問題是這些物件是受保護的，因此您必須創建一個新的滾動條類來設定這些事件。TScrollBar 建構式中尚不存在子物件，因此我發現分配它們的最佳位置是在第一個繪制事件上。

幾周前我問了幾乎完全相同的問題。在這里查看我自己的答案。

FMX：TScrollBar MouseDown 和 MouseUp 事件未觸發

這是您的示例，現在可以使用了。我還用 4 個標簽替換了您的一個標簽，以便更輕松地查看哪些事件被呼叫。

回應滑鼠事件的新滾動條類：

unit ScrollBarMouse;

interface

uses
  System.Classes, System.UITypes, FMX.StdCtrls, FMX.Types;

type

  // A scroll bar that responds to mouse events
  TScrollBarMouse = class(TScrollBar)
  private
    FMouseEventsSet : Boolean;
  protected
    procedure Paint; override;
  public
    constructor Create(AOwner: TComponent); override;
  end;


implementation

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

  FMouseEventsSet := False;
end;

procedure TScrollBarMouse.Paint;
begin
  inherited;

  // Track and Buttons are not assigned in constructor, so set mouse events on first paint
  if not FMouseEventsSet and Assigned(Track) and Assigned(Track.Thumb)
    and Assigned(MinButton) and Assigned(MaxButton) then begin
    Track.OnMouseDown       := onm ouseDown;
    Track.OnMouseUp         := onm ouseUp;
    Track.OnMouseMove       := onm ouseMove;
    Track.Thumb.OnMouseDown := onm ouseDown;
    Track.Thumb.OnMouseUp   := onm ouseUp;
    Track.Thumb.OnMouseMove := onm ouseMove;
    MinButton.OnMouseDown   := onm ouseDown;
    MinButton.OnMouseUp     := onm ouseUp;
    MinButton.OnMouseMove   := onm ouseMove;
    MaxButton.OnMouseDown   := onm ouseDown;
    MaxButton.OnMouseUp     := onm ouseUp;
    MaxButton.OnMouseMove   := onm ouseMove;
    FMouseEventsSet := True;
  end;
end;

end.

表格單位：

unit Unit1;

interface

uses
  System.SysUtils, System.Types, System.UITypes, System.Classes, System.Variants,
  FMX.Types, FMX.Controls, FMX.Forms, FMX.Graphics, FMX.Dialogs,
  FMX.Controls.Presentation, FMX.StdCtrls, ScrollBarMouse;

type

TForm4 = class(TForm)
    Label1: TLabel;
    Label2: TLabel;
    Label3: TLabel;
    Label4: TLabel;
    procedure ScrollBar1MouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Single);
    procedure ScrollBar1MouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Single);
    procedure ScrollBar1MouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Single);
    procedure ScrollBar1Change(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
    ScrollBar1 : TScrollBarMouse;
  end;

var
  Form4: TForm4;

implementation

{$R *.fmx}

procedure TForm4.FormCreate(Sender: TObject);
begin
  // Create the scroll bar object
  ScrollBar1 := TScrollBarMouse.Create(Self);
  with ScrollBar1 do begin
    Parent := Self;
    Orientation := TOrientation.Vertical;
    Position.X := 616;
    Position.Y := 8;
    Size.Width := 18;
    Size.Height := 449;
    onm ouseDown := ScrollBar1MouseDown;
    onm ouseUp := ScrollBar1MouseUp;
    onm ouseMove := ScrollBar1MouseMove;
    OnChange := ScrollBar1Change;
  end;
end;

procedure TForm4.ScrollBar1Change(Sender: TObject);
begin
  Label1.Text := 'onChange: '   IntToStr(Round(Screen.MousePos.Y));
end;

procedure TForm4.ScrollBar1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Single);
begin
  Label2.Text := 'mousedown: '   IntToStr(Round(Y));
end;

procedure TForm4.ScrollBar1MouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Single);
begin
  Label3.Text := 'mousemove: '   IntToStr(Round(Y));
end;

procedure TForm4.ScrollBar1MouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Single);
begin
  Label4.Text := 'mouseUP: '   IntToStr(Round(Y));
end;

end.

表單（滾動條被洗掉，因為它是在運行時創建的）：

object Form4: TForm4
  Left = 0
  Top = 0
  Caption = 'Form4'
  ClientHeight = 480
  ClientWidth = 640
  FormFactor.Width = 320
  FormFactor.Height = 480
  FormFactor.Devices = [Desktop]
  OnCreate = FormCreate
  DesignerMasterStyle = 0
  object Label1: TLabel
    Position.X = 424.000000000000000000
    Position.Y = 144.000000000000000000
    Size.Width = 121.000000000000000000
    Size.Height = 17.000000000000000000
    Size.PlatformDefault = False
    Text = 'Label1'
    TabOrder = 3
  end
  object Label2: TLabel
    Position.X = 424.000000000000000000
    Position.Y = 168.000000000000000000
    Size.Width = 121.000000000000000000
    Size.Height = 17.000000000000000000
    Size.PlatformDefault = False
    Text = 'Label1'
    TabOrder = 2
  end
  object Label3: TLabel
    Position.X = 424.000000000000000000
    Position.Y = 192.000000000000000000
    Size.Width = 121.000000000000000000
    Size.Height = 17.000000000000000000
    Size.PlatformDefault = False
    Text = 'Label1'
    TabOrder = 1
  end
  object Label4: TLabel
    Position.X = 424.000000000000000000
    Position.Y = 216.000000000000000000
    Size.Width = 121.000000000000000000
    Size.Height = 17.000000000000000000
    Size.PlatformDefault = False
    Text = 'Label1'
    TabOrder = 0
  end
end

這是使用 Delphi 10.4 構建的，并在 Windows 10 中運行。

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