我正在尝试将IEnuemrable<SystemUser>的类型检查为null。
我正在使用这段代码
var systemUsers = newActActivityPersons.SelectMany(x => x.Person.SystemUsers);
if (systemUsers == null || !systemUsers.Any()) return ;
这不起作用。当我尝试执行systemUsers.ToArray()或systemUsers.ToList()之类的操作时，我会得到一个null异常。如何查看错误？
答案 0 :(得分：0)
后续x.Person.SystemUsers之一可能为空。如果有.Any()，则返回true。如果您之后尝试ToList()，则可能会发现x Person为x.Person为空。
检查以确保while(1){
listen(sockfd,5);
// determine the size of a clientAddressInfo struct
clilen = sizeof(clientAddressInfo);
int *newsockfd = malloc(sizeof(int));
// block until a client connects, when it does, create a client socket
*newsockfd = accept(sockfd, (struct sockaddr *) &clientAddressInfo, &clilen);
// if the connection blew up for some reason, complain and exit
if (*newsockfd < 0){
error("ERROR on accept");
}
connection_args *args = malloc(sizeof(connection_args));
args->file_descrp = newsockfd;
pthread_t tid;
pthread_create(&tid,NULL, handle_connect, args);
}
void * handle_connect(void* args){
connection_args* connect_arg = (connection_args*)args;
pthread_detach(pthread_self());
int n = -1;
char buffer[256];
bzero(buffer,256);
//while not close;
while(1){
// try to read from the client socket
n = read(*connect_arg->file_descrp,buffer,255);
printf("input: %s\n", buffer);
// if the read from the client blew up, complain and exit
if (n < 0){
error("ERROR reading from socket");
}
int fd;
if(strcmp("open",buffer) == 0){
fd = open("file.txt",0);
bzero(buffer,256);
sprintf(buffer,"%d",fd);
}else if(strcmp("read",buffer) == 0){
char *read_buffer = malloc(sizeof(char)*256);
bzero(read_buffer,256);
fd = read(get_filedescrp(),read_buffer,30);
bzero(buffer,256);
sprintf(buffer,"%s,%d",read_buffer,fd);
}else if(strcmp("close",buffer) == 0){
break;
}
printf("buffer_send: %s\n",buffer);
// try to write to the client socket
n = write(*connect_arg->file_descrp,buffer,sizeof(buffer));
// if the write to the client below up, complain and exit
if (n < 0){
printf("here!!\n");
error("ERROR writing to socket");
}
bzero(buffer,256);
}
printf("Left thread\n");
return NULL;
}
在访问对象上的属性之前不为空。