删除前导逗号

Question

我正在将信息从sqlite数据库读取到.csv文件中。我能够获得要构建的文件，但是每个新行都以"，“开头。我做过一些android编程，但ios不多。我认为问题是componentsJoinedByString:@"，“因为它将所有东西连接在一起，但我不确定如何消除使用this的每个新行开头的"，”。有没有其他方法可以将它们连接到csv文件中，或者去掉第一个逗号？

NSMutableArray *exportBike = [[NSMutableArray alloc] init];

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

NSString *docsPath = [paths objectAtIndex:0];

NSString *path = [docsPath stringByAppendingPathComponent:@"MemberDB.sql"];

FMDatabase *database = [FMDatabase databaseWithPath:path];

[database open];

FMResultSet *resultsBike = [database executeQuery:@"SELECT * FROM bike"];

while([resultsBike next]) {

    NSString *name = [resultsBike stringForColumn:@"name"];
    NSInteger stage1HR  = [resultsBike intForColumn:@"stage1HR"];
    NSInteger stage1BP = [resultsBike intForColumn:@"stage1BP"];
    NSInteger stage2HR = [resultsBike intForColumn:@"stage2HR"];
    NSInteger stage2BP = [resultsBike intForColumn:@"stage2BP"];
    NSInteger stage3HR  = [resultsBike intForColumn:@"stage3HR"];
    NSInteger stage3BP = [resultsBike intForColumn:@"stage3BP"];
    NSInteger stage4HR  = [resultsBike intForColumn:@"stage4HR"];
    NSInteger stage4BP = [resultsBike intForColumn:@"stage4BP"];
    NSInteger stage5HR  = [resultsBike intForColumn:@"stage5HR"];
    NSInteger stage5BP = [resultsBike intForColumn:@"stage5BP"];
    NSInteger stage6HR  = [resultsBike intForColumn:@"stage6HR"];
    NSInteger stage6BP = [resultsBike intForColumn:@"stage6BP"];
    NSInteger stage7HR  = [resultsBike intForColumn:@"stage7HR"];
    NSInteger stage7BP = [resultsBike intForColumn:@"stage7BP"];
    NSInteger recoveryHR = [resultsBike intForColumn:@"recoveryHR"];

    NSLog(@"%@,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d",name, stage1HR, stage1BP, stage2HR, stage2BP, stage3HR, stage3BP, stage4HR, stage4BP, stage5HR, stage5BP, stage6HR, stage6BP, stage7HR, stage7BP, recoveryHR);

    [exportBike addObject:[NSString stringWithFormat:@"%@,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d""\n",name, stage1HR, stage1BP, stage2HR, stage2BP, stage3HR, stage3BP, stage4HR, stage4BP, stage5HR, stage5BP, stage6HR, stage6BP, stage7HR, stage7BP, recoveryHR]];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    NSString *savePath = [paths objectAtIndex:0];

    savePath = [savePath stringByAppendingPathComponent:@"bike.csv"];

    [[exportBike componentsJoinedByString:@","] writeToFile:savePath atomically:YES encoding:NSUTF8StringEncoding error:NULL];

Answer 1

变化

[exportBike addObject:[NSString stringWithFormat:@"%@,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d""\n",name, stage1HR, stage1BP, stage2HR, stage2BP, stage3HR, stage3BP, stage4HR, stage4BP, stage5HR, stage5BP, stage6HR, stage6BP, stage7HR, stage7BP, recoveryHR]];

[[exportBike componentsJoinedByString:@","] writeToFile:savePath atomically:YES encoding:NSUTF8StringEncoding error:NULL];

至

[exportBike addObject:[NSString stringWithFormat:@"%@,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d",name, stage1HR, stage1BP, stage2HR, stage2BP, stage3HR, stage3BP, stage4HR, stage4BP, stage5HR, stage5BP, stage6HR, stage6BP, stage7HR, stage7BP, recoveryHR]];

[[exportBike componentsJoinedByString:@"\n"] writeToFile:savePath atomically:YES encoding:NSUTF8StringEncoding error:NULL];

在componentsJoinedByString方法中使用"\n"而不是","，并在addObject行中删除末尾的"\n"。

正如马丁在下面提到的，另一种选择是将换行符保留在addObject行中，并使用[exportBike componentsJoinedByString:@""]。这将在文件的末尾添加一个新行字符。