将yyyy-MM-dd HH:mm:ss格式时间转换成时间戳

+(long)changeTimeToTimeSp:(NSString *)timeStr{
long time;
NSDateFormatter *format=[[NSDateFormatter alloc] init];
[format setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSDate *fromdate=[format dateFromString:timeStr];
time= (long)[fromdate timeIntervalSince1970];

return time;

}