只能输入数字

 procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: Char);
var p:integer; tp:TPoint;
begin
   if key in ['0'..'9','+','-','.'] then
   //是否是0-9，以及是否为+、-号
      begin
         if key in ['+','-'] then
            begin
               p:=pos('+',Edit1.Text)+pos('-',Edit1.Text);
               if p>0 then key:=#0
               else
                  begin
                     GetCaretPos(tp);
                     if tp.x>1 then key:=#0;
                  end;
            end
         else
if key='.' Then
//判断是否为小数点
               begin
                  p:=pos('.',Edit1.Text);
                  if p>0 then key:=#0;
               end;
      end
   else if key>#31 then key:=#0;
end;