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好吧，基本上我有一個運行循環在我的應用程序中每隔一兩秒進行一次，而同時我有另一個線程正在循環通過listenForPackets方法; broadcastMessage僅在另一個操作方法發生時才啓動。這個問題的重要部分是，當監聽器線程獨立於主線程運行時，它永遠不會打印出任何打印命令，並且它似乎不允許訪問我定義的名爲recvMessage的全局變量，它位於接口和實現部分。可以通過一個Objective-C的NSThread訪問全局變量嗎？
在我的代碼中，我將它設置爲每當它運行通過主運行循環時，它都會在我的GUI中更新一個UILabel。當應用程序運行時，我的標籤始終保持空白，並且永遠不會更改。我已經對GUI進行了雙重檢查，並且所有內容都正確鏈接，並且我的標籤也正確實例化了（我在下面的代碼中使用名稱「label」作爲UILabel的一個實例）。有沒有人有任何想法，爲什麼我的標籤正在更新？事情的網絡方面是好的，我相信，因爲我剛剛完成了這一切，一切都在「交談」。也許這是一個我不知道的變量範圍問題，或者是允許訪問全局變量的獨立線程，比如我在下面使用的變量（rcvMessage）？我對多線程應用程序相當陌生，但我不認爲使用NSThread（只有一行代碼）實現起來真的很難。
全局變量
NSString *recvMessage;
主要Runloop - 即每次穿過runloop
發話方法
-(void)broadcastMessage { // (NSString*)msg {
msg = @"From_Master";
NSLog(@"broadcastMessage - Stage 1");
mc_ttl = 15; // number of node hops the message is allowed to travel across the network
// define the port we will be using
mc_port = MYPORT;
// create a socket for sending to the multicast address
if ((sock = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
NSLog(@"ERROR: broadcastMessage - socket() failed");
return;
}
memset(&mc_addr, 0, sizeof(mc_addr));
mc_addr.sin_family = AF_INET;
mc_addr.sin_addr.s_addr = inet_addr(GROUP_ADDRESS);
mc_addr.sin_port = htons(MYPORT);
NSLog(@"broadcastMessage - Stage 2");
// set the TTL (time to live/hop count) for the send
if ((setsockopt(sock, IPPROTO_IP, IP_MULTICAST_TTL, &mc_ttl, sizeof(mc_ttl))) < 0) {
NSLog(@"ERROR: broadcastMessage - setsockopt() failed");
return;
}
NSLog(@"broadcastMessage - Stage 3");
// clear send buffer
memset(send_str, 0, sizeof(send_str));
// convert the message to a C string to send
[msg getCString:send_str maxLength:MAX_LEN encoding:NSASCIIStringEncoding];
//while (fgets(send_str, MAX_LEN, stdin)) {
NSLog(@"broadcastMessage - Stage 4");
NSLog(@"Message =");
printf(send_str);
// send string to multicast address
if ((sendto(sock, send_str, sizeof(send_str), 0, (struct sockaddr *)&mc_addr, sizeof(mc_addr))) < 0) {
NSLog(@"ERROR: broadcastMessage - sendto() sent incorrect number of bytes");
//return;
}
NSLog(@"Sent Message -");
printf(send_str);
NSLog(@"broadcastMessage - Stage 5");
// clear send buffer
memset(send_str, 0, sizeof(send_str));
NSLog(@"broadcastMessage - Stage 6 - Complete");
close(sock);
}
監聽方法
時間更新標籤的部分-(void)listenForPackets {
listeningFlag_on = 1; // allows reuse of the same socket
NSLog(@"listenForPackets - Stage 1");
if ((listeningSock = socket(AF_INET, SOCK_DGRAM,IPPROTO_UDP)) < 0) {
NSLog(@"ERROR: listenForPackets - socket() failed");
return;
// make the method return an int instead of void and use this statement to check for errors
}
NSLog(@"listenForPackets - Stage 2");
// set reuse port to on to allow multiple binds per host
if ((setsockopt(listeningSock, SOL_SOCKET, SO_REUSEADDR, &listeningFlag_on, sizeof(listeningFlag_on))) < 0) {
NSLog(@"ERROR: listenForPackets - setsockopt() Reuse failed");
return;
// make the method return an int instead of void and use this statement to check for errors
}
// construct a multicast address structure after erasing anything in the listeningmc_addr structure
memset(&listeningmc_addr, 0, sizeof(listeningmc_addr));
listeningmc_addr.sin_family = AF_INET;
listeningmc_addr.sin_addr.s_addr = htonl(INADDR_ANY); // different from sender
listeningmc_addr.sin_port = htons(MYPORT);
// bind multicast address to socket
if ((bind(listeningSock, (struct sockaddr *)&listeningmc_addr, sizeof(listeningmc_addr))) < 0) {
NSLog(@"ERROR: listenForPackets - bind() failed");
perror("Bind() -");
return; // make the method return an int instead of void and use this statement to check for errors
}
//*********************************************************************************
NSString *ipAddress = [[NSString alloc] initWithString:self.getIPAddress];
const char *tmp = [ipAddress UTF8String];
listeningMc_addr_str = tmp;
printf("%s\n", listeningMc_addr_str);
listeningMc_req.imr_multiaddr.s_addr = inet_addr(GROUP_ADDRESS);
listeningMc_req.imr_interface.s_addr = htonl(INADDR_ANY);
// send an ADD MEMBERSHIP message via setsockopt
if ((setsockopt(listeningSock, IPPROTO_IP, IP_ADD_MEMBERSHIP, &listeningMc_req, sizeof(listeningMc_req))) < 0) {
NSLog(@"ERROR: listenForPackets - setsockopt() failed");
int err = errno;
NSLog(@"errno - %i", err);
NSLog(@"Error = %s", strerror(err));
perror("ERROR");
return; // make the method return an int instead of void and use this statement to check for errors
}
NSLog(@"listenForPackets - Stage 3");
for (;;) { // loop forever
// clear the receive buffers & structs
memset(listeningRecv_str, 0, sizeof(listeningRecv_str));
listeningFrom_len = sizeof(listeningFrom_addr);
memset(&listeningFrom_addr, 0, listeningFrom_len);
NSLog(@"Test #1 Complete");
//msgStatus.text = @"Waiting...";
// block waiting to receive a packet
listeningFrom_len = sizeof(listeningmc_addr);
if ((listeningRecv_len = recvfrom(listeningSock, listeningRecv_str, MAX_LEN, 0, (struct sockaddr*)&listeningmc_addr, &listeningFrom_len)) < 0) {
NSLog(@"ERROR: listenForPackets - recvfrom() failed");
return; // make the method return an int instead of void and use this statement to check for errors
}
NSLog(@"Test #2 Complete - Received a Message =");
NSLog(@"listenForPackets - Stage 4");
// listeningRecv_str
**tmpString = [[NSString alloc] initWithCString:listeningRecv_str encoding:NSASCIIStringEncoding];
NSLog(@"Message Received =");
NSLog(tmpString);
recvMessage = tmpString;**
//}
// received string
printf("Received %d bytes from %s: ", listeningRecv_len, inet_ntoa(listeningFrom_addr.sin_addr));
printf("%s", listeningRecv_str);
//}
}
// send a DROP MEMBERSHIP message via setsockopt
if ((setsockopt(listeningSock, IPPROTO_IP, IP_DROP_MEMBERSHIP, (void*) &listeningMc_req, sizeof(listeningMc_req))) < 0) {
NSLog(@"ERROR: listenForPackets - setsockopt() drop membership failed");
//return 1; // make the method return an int instead of void and use this statement to check for errors
}
close(listeningSock);
NSLog(@"listenForPackets - Stage 5 - Complete");
}
如果您剝離了所有不相關的套接字代碼並只發布與您的問題相關的部分，這個問題對於人們來說會更容易回答。 – smorgan 2009-07-25 23:24:37