objective-c - NSArrayController 为什么这不起作用？

Question

我正在尝试编写一个例程，将制表符分隔的文件中的数百条客户记录导入到 NSArrayController 中。

这是我的初始代码:

NSString *stringFromFile = [NSString stringWithContentsOfFile:[fileURL path]
                                encoding:NSUTF8StringEncoding error:&error];
NSArray *paragraphsArray = [stringFromFile componentsSeparatedByString:@"\r"];
NSMutableDictionary *destDict = [[NSMutableDictionary alloc] init];

int i;
for (i = 0; i <= [paragraphsArray count]-1; i++) {
    NSString *currentParagraph = [paragraphsArray objectAtIndex:i];
    if ([currentParagraph length ] > 4) {
        NSArray *elementsArray = [currentParagraph componentsSeparatedByString:@"\t"];
        if ([elementsArray count] > 0) {
            currentSerial++;
            [destDict setObject:[NSString stringWithFormat:@"%ld",currentSerial]
                         forKey:@"idSerial"];
            [destDict setObject:[elementsArray objectAtIndex:1]
                         forKey:@"destRazaoSocial"];
            [destDict setObject:[elementsArray objectAtIndex:2]
                         forKey:@"destLogradouro"];
            [destDict setObject:[elementsArray objectAtIndex:3]
                         forKey:@"destLogradouroNro"];
            /// repeat this for every field...
            //Add the record:
            [destArrayController addObject:destDict];
        }
    }
}

这段代码会导致记录插入错误，如果我的例子中有4条记录，则插入的4条记录将与最后一条记录的内容相同。

但是如果我将代码更改为这样，分配 destDict 并在每个循环中丢弃它，它就会起作用:

NSString *stringFromFile = [NSString stringWithContentsOfFile:[fileURL path]
                                   encoding:NSUTF8StringEncoding error:&error];
NSArray *paragraphsArray = [stringFromFile componentsSeparatedByString:@"\r"];
int i;
for (i = 0; i <= [paragraphsArray count]-1; i++) {
    NSString *currentParagraph = [paragraphsArray objectAtIndex:i];
    if ([currentParagraph length ] > 4) {
        NSArray *elementsArray = [currentParagraph componentsSeparatedByString:@"\t"];
        if ([elementsArray count] > 0) {
            NSMutableDictionary *destDict = [[NSMutableDictionary alloc] init];
            currentSerial++;
            [destDict setObject:[NSString stringWithFormat:@"%ld",currentSerial]
                         forKey:@"idSerial"];
            [destDict setObject:[elementsArray objectAtIndex:1]
                         forKey:@"destRazaoSocial"];
            [destDict setObject:[elementsArray objectAtIndex:2]
                         forKey:@"destLogradouro"];
            [destDict setObject:[elementsArray objectAtIndex:3]
                         forKey:@"destLogradouroNro"];
            /// repeat this for every field...
            //Add the record:
            [destArrayController addObject:destDict];
            [destDict release];
        }
    }
}

这可行，但对我来说看起来并不优雅。您能告诉我正确的方法吗？

Answer 1

按照您发布的第二种方式进行操作没有任何问题。另一种方法(可能会或可能不会更好)是第一种方法，但将 [destDict copy] 而不是 destDict 添加到数组中。

关于 for 循环的另一点 - 如果您不需要使用索引(代码中不需要)，则应该使用快速枚举。写起来更快更容易。所以，这个:

int i;
for (i = 0; i <= [paragraphsArray count]-1; i++) {
    NSString *currentParagraph = [paragraphsArray objectAtIndex:i];

可以这样完成(称为 for-in 循环):

for (NSString *currentParagraph in paragraphArray){
    ....
    ....
}