ARTSPConnection对RTSP流的连接过程

　　下面贴出安卓N版本ARTSPConnection::connect的调用流程：

　　

==>
void ARTSPConnection::connect(const char *url, const sp<AMessage> &reply) {
//新建消息msg，消息名为kWhatConnect，消息的处理者为this也就是ARTSPConnection
//那么，消息名为kWhatConnect消息的处理则会在ARTSPConnection::onMessageReceived 的case kWhatConnect处理分支中
//将传进来的两个参数url和reply消息引用分别添加到msg消息的"url"和"reply"字段中
sp<AMessage> msg = new AMessage(kWhatConnect, this);
msg->setString("url", url);
msg->setMessage("reply", reply);
msg->post();
}　

==>
void ARTSPConnection::onMessageReceived(const sp<AMessage> &msg) {
switch (msg->what()) {
case kWhatConnect:
//调用onConnect(msg)函数对该消息进行处理完成后续的连接
onConnect(msg);
break;

case kWhatDisconnect:
onDisconnect(msg);
break;

case kWhatCompleteConnection:
onCompleteConnection(msg);
break;

case kWhatSendRequest:
onSendRequest(msg);
break;

case kWhatReceiveResponse:
onReceiveResponse();
break;

case kWhatObserveBinaryData:
{
CHECK(msg->findMessage("reply", &mObserveBinaryMessage));
break;
}

default:
TRESPASS();
break;
}
}

==>
void ARTSPConnection::onConnect(const sp<AMessage> &msg) {
++mConnectionID;

//初次调用onConnect函数必须是DISCONNECTED状态，否则进行相应的异常处理
if (mState != DISCONNECTED) {
if (mUIDValid) {
HTTPBase::UnRegisterSocketUserTag(mSocket);
HTTPBase::UnRegisterSocketUserMark(mSocket);
}
close(mSocket);
mSocket = -1;

flushPendingRequests();
}

//将状态设置为CONNECTING状态，表示正在进行连接
mState = CONNECTING;

//从消息里得到参数url和reply消息（注：此消息的消息名为"conn"，消息的处理者为MyHandler）
AString url;
CHECK(msg->findString("url", &url));

sp<AMessage> reply;
CHECK(msg->findMessage("reply", &reply));

//调用ParseURL函数从url.c_str()里解析出主机号host，路径path，端口号port
//其中主机号host，路径path是AString类型的字符串，port是unsigned类型的整数
//具体是如何解析的后续文章会向大家介绍
AString host, path;
unsigned port;
if (!ParseURL(url.c_str(), &host, &port, &path, &mUser, &mPass)
|| (mUser.size() > 0 && mPass.size() == 0)) {
// If we have a user name but no password we have to give up
// right here, since we currently have no way of asking the user
// for this information.

ALOGE("Malformed rtsp url %s", uriDebugString(url).c_str());

reply->setInt32("result", ERROR_MALFORMED);
reply->post();

mState = DISCONNECTED;
return;
}

if (mUser.size() > 0) {
ALOGV("user = '%s', pass = '%s'", mUser.c_str(), mPass.c_str());
}
host
//传递参数reply消息，主机号host，和端口号port来调用函数performConnect完成连接
performConnect(reply, host, port);
}

　　小结：ARTSPConnection::onConnect函数是对ARTSPConnection::connect发送的消息名为kWhatConnect的处理。具体处理的事情是获取到reply消息的引用（该消息的消息名为”conn”，消息的处理者为MyHandler），获取到参数url，从参数url里解析出主机号host，路径path，端口号port，然后调用函数performConnect(reply, host, port)来完成RTSP流的连接。