Message.Msg, WM_LBUTTONDBLCLK , WM_LBUTTONDOWN
这些都是integer类型的常量
Decrements a variable by 1 or N.//变量减去1orN
Unit
System
Category
ordinal routines
Delphi syntax:
procedure Dec(var X[
N: Longint]);
Description
In Delphi code, Dec subtracts one or N from a variable.
X is a variable of an ordinal type (including Int64), or a pointer type if the extended syntax is enabled.
N is an integer-type expression.
X decrements by 1, or by N if N is specified
that is, Dec(X) corresponds to the statement X := X - 1, and Dec(X, N) corresponds to the statement X := X - N. However, Dec generates optimized code and is especially useful in tight loops.
Note: If X is a pointer type, it decrements X by N times the size of the type pointed to. Thus, given
type
PMytype = ^TMyType;
and
var
P: PMyType;
the statement
Dec(P);
decrements P by SizeOf(TMyType).
Warning: Do not use Dec on ordinal-type properties if the property uses a write procedure.
