iphone - NSSortDescriptor 根本无法计算数字

Question

有了这个

    NSSortDescriptor *lessonDescriptor = [[NSSortDescriptor alloc] initWithKey:@"lesson" ascending:YES];
[resultArray sortUsingDescriptors:[NSArray arrayWithObject:lessonDescriptor]];

它正在对“类(class)”对象进行排序

(
    {
    lesson = 9;
    subject = bg;
},
    {
    lesson = 8;
    subject = bg;
},
    {
    lesson = 11;
    subject = CAE;
},
    {
    lesson = 11;
    subject = CAE;
},
    {
    lesson = 10;
    subject = CAE;
},
    {
    lesson = 10;
    subject = CAE;
},
    {
    lesson = 5;
    subject = Gg;
},
    {
    lesson = 4;
    subject = G;
},
    {
    lesson = 3;
    subject = G;
},
    {
    lesson = 2;
    subject = M;
},
    {
    lesson = 1;
    subject = M;
}

)

如您所见，它没有正确计数。有人可以帮忙吗？

非常感谢

编辑:

不知道如何实现值的东西 =)

else if ([currentElement isEqualToString:@"lesson"]) 
{ 

    NSString *trimmedString = [string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
    NSLog(@"trimmed: %@",trimmedString);
    int value = [trimmedString intValue];   ??
    [currentSummary appendString:value];  ??

    [currentSummary appendString:trimmedString]; 
} 

Answer 1

为了使排序描述符正常工作，您必须在将“类(class)”转换为数字之前修剪字符串。否则，排序描述符只能看到字符串值而不是数字。这是删除空格和换行符的方法:

NSString *stringValue = [parsedValue stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

调用 [stringValue intValue] 将得到字符串的整数值

int value = [stringValue intValue];

在此属性上调用排序描述符之前，将此值保存到数组中。

告诉我它是否有效。