为什么在设计时找不到TServerSocket类？

Question

In Comm_Ethernet.dfm I declare a component of type TServerSocket :

object frmCommEthernet: TfrmCommEthernet
  object ServerSocket1: TServerSocket
    Active = False
    Port = 5555
    ServerType = stNonBlocking
    OnClientConnect = ServerSocket1ClientConnect
    OnClientDisconnect = ServerSocket1ClientDisconnect
    OnClientRead = ServerSocket1ClientRead
    OnClientError = ServerSocket1ClientError
    Left = 808
    Top = 8
  end
end

TServerSocket is declared in unit System.Win.ScktComp which is in the RTL, but it doesn't seem to be available at design-time because when I open my form it complains:

TServerSocket class not found [Ignore] [Cancel] [Ignore All]

However my project compiles and runs just fine (when this form is not open in the IDE). How do I get rid of this error?

Answer 1

The components in ScktComp are deprecated and have been for a long time. You are expected to use different components, for instance Indy. One strong reason for the deprecation is that these components are not cross-platform.

You can still use the ScktComp components at designtime if you install the dclsocketsNNN.bpl package into the IDE. Presumably Embarcadero doesn't install this package by default because it contains deprecated components.

Answer 2

For whatever reason, by default, the BPL package containing this unit is not installed in the IDE.

You must go:

Components -> Install Packages -> Add

Then select dclsockets160.bpl in Embarcadero\\RAD Studio\\9.0\\bin (change according to your Delphi version)

How to find out in whic RTL BPL package a unit is contained is a mystery to me; it doesn't seem to be documented anywhere.