iphone - NSMutableArray addObject，无法识别的选择器

Question

我正在尝试创建数组(城市)的数组(州)。每当我尝试向我的 City 数组添加一个项目时，我都会收到此错误:

'NSInvalidArgumentException', reason: '*** +[NSMutableArray addObject:]: unrecognized selector sent to class 0x303097a0

我的代码如下。它出错的行是

 [currentCities addObject:city];

我确定我遇到了一些内存管理问题，因为我仍然不太了解它。希望有人能向我解释我的错误。

if (sqlite3_prepare_v2(db, sql, -1, &statement, NULL) == SQLITE_OK){
        // We need to keep track of the state we are on
        NSString *state = @"none";
        NSMutableArray *currentCities = [NSMutableArray alloc];

        // We "step" through the results - once for each row
        while (sqlite3_step(statement) == SQLITE_ROW){
            // The second parameter indicates the column index into the result set.
            int primaryKey = sqlite3_column_int(statement, 0);
            City *city = [[City alloc] initWithPrimaryKey:primaryKey database:db];

            if (![state isEqualToString:city.state])
            {
                // We switched states
                state = [[NSString alloc] initWithString:city.state]; 

                // Add the old array to the states array
                [self.states addObject:currentCities];

                // set up a new cities array
                currentCities = [NSMutableArray init];
            }

            [currentCities addObject:city];
            [city release];
        }
    }

Answer 1

线条:

// set up a new cities array
currentCities = [NSMutableArray init];

应阅读:

// set up a new cities array
[currentCities init];

这应该有望解决您的问题。您不是初始化数组，而是向类对象发送初始化消息，该类对象不执行任何操作。之后，您的 currentCities 指针仍未初始化。

更好的方法是删除该行并更改第 4 行，这样您就可以一步分配和初始化所有内容:

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