procedure TForm1.TreeView1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
Var
  HitTest : THitTests;
begin
  HitTest := GetHitTestInfoAt(X, Y);
  If htOnItem IN HitTest Then Begin  // 點在Item上
  End Else If ..... IN HitTest Then Begin    // 偵測其位置
  ....
  End;
end;      摘錄自Delphi HELP
// =============================================================
THitTest and THitTests are used in the GetHitTestInfoAt method.    Unit    ComCtrls or QComCtrls    Delphi syntax:    type
  THitTest = (htAbove, htBelow, htNowhere, htOnItem, htOnButton, htOnIcon, htOnIndent, htOnLabel, htOnRight, htOnStateIcon, htToLeft, htToRight);
  THitTests = set of THitTest;    Description    THitTests is a set of THitTest values. THitTest can have any of the following values:    Value        Means the point is    htAbove        Above the client area.
htBelow        Below the client area.
htNowhere        Inside the control, but not on an item.
htOnItem        On an item, its text, or its bitmap.
htOnButton        On a button.
htOnIcon        On an icon.
htOnIndent        On the indented area of an item.
htOnLabel        On a label.
htOnRight        On the right side of an item.
htOnStateIcon        On a state icon or bitmap associated with an item.
htToLeft        To the left of the client area.
htToRight        To the right of the client area.    

procedure TForm1.TreeView1MouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
Var
  HitTest : THitTests;
begin
  HitTest := TListView(Sender).GetHitTestInfoAt(X, Y);
  If htOnItem IN HitTest Then Begin  // 點在Item上
  End Else If ..... IN HitTest Then Begin    // 偵測其位置
  ....
  End;
end;

  HitTest := TListView(Sender).GetHitTestInfoAt(X, Y);
  If htOnItem IN HitTest Then Begin  // 點在Item上(Caption及icon)
    // Do Something
  End Else If ..... IN HitTest Then Begin    // 偵測其他位置
    // Do Something
  ....
  ....
  ....
  End;