简单扼要，主要简单介绍到xmpp中的presence

  表示XMPP状态的packet。每一个presence都有一个状态。用枚举类型Presence.Type的值表示:

available --(默认)用户空闲状态

unavailable--用户没空看消息

subscribe--请求加别人为好友

subscribed--确认别人对自己的好友请求

unsubscribe--请求删除好友

unsubscribed--拒绝对方的添加请求

error --当前状态packet有错误

内嵌两个Presence.Mode 和Presence.Type。可以使用setStatus自定义当前的状态

小例子：

加好友

//添加好友
#pragma mark 加好友
- (void)XMPPAddFriendSubscribe:(NSString *)name
{
    //XMPPHOST 就是服务器名，  主机名
    NSXMLElement *mes = [NSXMLElement elementWithName:@"presence"];
            
            
    [mes addAttributeWithName:@"xmlns" stringValue:@"jabber:client"];
    //消息类型
    [mes addAttributeWithName:@"type" stringValue:@"subscribe"];
    [mes addAttributeWithName:@"to" stringValue:name];
    [mes addAttributeWithName:@"from" stringValue:[NSString stringWithFormat:@"%@@%@",[[ShpadDataCenter AppData] loginname],@"ay130415223308469c09"]];
            
    //发送消息
    [[[ShpadXMPPService sharedInstance] xmppStream] sendElement:mes];
            
}

//定义删除好友XMPP
#pragma mark 加好友
- (void)XMPPDeleteFriendSubscribe:(NSUInteger)row
{
   //XMPPHOST 就是服务器名，  主机名
   NSXMLElement *mes = [NSXMLElement elementWithName:@"presence"];


   [mes addAttributeWithName:@"xmlns" stringValue:@"jabber:client"];
   //消息类型
   [mes addAttributeWithName:@"type" stringValue:@"unsubscribe"];
   [mes addAttributeWithName:@"to" stringValue:[(BuddyEntity *)[self._allFriends objectAtIndex:row] userId]];
   [mes addAttributeWithName:@"from" stringValue:[NSString stringWithFormat:@"%@@%@",[[ShpadDataCenter AppData] loginname],@"ay130415223308469c09"]];

   //发送消息
   [[[ShpadXMPPService sharedInstance] xmppStream] sendElement:mes];


}

//定义删除好友XMPP
#pragma mark 删除好友
- (void)XMPPDeleteFriendSubscribe:(NSUInteger)row
{
    //XMPPHOST 就是服务器名，  主机名
    NSXMLElement *mes = [NSXMLElement elementWithName:@"presence"];
        
        
    [mes addAttributeWithName:@"xmlns" stringValue:@"jabber:client"];
    //消息类型
    [mes addAttributeWithName:@"type" stringValue:@"unsubscribe"];
    [mes addAttributeWithName:@"to" stringValue:[(BuddyEntity *)[self._allFriends objectAtIndex:row] userId]];
    [mes addAttributeWithName:@"from" stringValue:[NSString stringWithFormat:@"%@@%@",[[ShpadDataCenter AppData] loginname],@"ay130415223308469c09"]];
        
    //发送消息
    [[[ShpadXMPPService sharedInstance] xmppStream] sendElement:mes];
        
}

//拒绝好友请求xmpp
#pragma mark 拒绝好友
- (void)XMPPRejectFriendSubscribe:(id) sender
{
    //XMPPHOST 就是服务器名，  主机名
    NSXMLElement *mes = [NSXMLElement elementWithName:@"presence"];
      
      
    [mes addAttributeWithName:@"xmlns" stringValue:@"jabber:client"];
    //消息类型
    [mes addAttributeWithName:@"type" stringValue:@"unsubscribed"];
    [mes addAttributeWithName:@"to" stringValue:[self.userInfo objectForKey:@"userName"]];
    [mes addAttributeWithName:@"from" stringValue:[NSString stringWithFormat:@"%@@%@",[[ShpadDataCenter AppData] loginname],@"ay130415223308469c09"]];
      
    //发送消息
    [[[ShpadXMPPService sharedInstance] xmppStream] sendElement:mes];
      
}