计算有效期字符串转NSDate 转字符串

//首先要处理后台给的字符串 转换成自己想要的格式
NSArray *array = [[NSString stringWithFormat:@"%@", @"2020-03-17T00:00:00Z"] componentsSeparatedByString:@"T"];
NSDateFormatter*df = [[NSDateFormatter alloc]init];//格式化
[df setDateFormat:@"YYYY-MM-dd HH:mm:ss"];
[df setLocale:[[NSLocale alloc]initWithLocaleIdentifier:@"zh_CN"] ];
        
NSDate*date =[[NSDate alloc]init];
        
NSString *string = [[NSString stringWithFormat:@"%@", array[0]] stringByAppendingString:[[NSString stringWithFormat:@" %@", array[1]] substringWithRange:NSMakeRange(0, [NSString stringWithFormat:@"%@", array[1]].length - 1)]];
        
date =[df dateFromString:[NSString stringWithFormat:@"%@", string]];
//转换成秒
NSTimeInterval timeStamp= [date timeIntervalSince1970];
        
NSLog(@"%@", array[0]);
[11:43:06] -[PersonalTrainingMembersBaseTableViewCell setModel:] [第191行] 2017-03-31

NSLog(@"%@", string);
[11:43:06] -[PersonalTrainingMembersBaseTableViewCell setModel:] [第192行] 2017-03-31 00:00:0

NSLog(@"%f", timeStamp);
[11:43:06] -[PersonalTrainingMembersBaseTableViewCell setModel:] [第193行] 1490889600.000000      


//获取当前日期
NSDate *dateToday = [NSDate date];
        
NSDateFormatter  *dateformatter=[[NSDateFormatter alloc] init];
        
[dateformatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"];
        
NSString *timeTodayStr = [dateformatter stringFromDate:dateToday];
        
NSTimeInterval timeStamp1= [dateToday timeIntervalSince1970];
        
NSLog(@"%@", timeTodayStr);
NSLog(@"%f", timeStamp1);
        
int time =   (timeStamp -timeStamp1) / 86400;
        
self.validityTimeLabel.text = [NSString stringWithFormat:@"会籍有效天数(天)：%d", time];