排序问题

NSMutableArray *ma1 = [[NSMutableArray alloc] init];
    [ma1 addObject:@"2"];
    [ma1 addObject:@"1"];
    [ma1 addObject:@"3"];
   
    NSSortDescriptor *sd1 = [NSSortDescriptor sortDescriptorWithKey:@"self" ascending:NO];
    NSArray *arr1 = [ma1 sortedArrayUsingDescriptors:[NSArray arrayWithObjects:sd1, nil]];
   
    for (NSString *str in arr1) {
        NSLog(@"%@", str);
    }
   
    NSMutableArray *ma2 = [[NSMutableArray alloc] init];
    [ma2 addObject:@"b"];
    [ma2 addObject:@"c"];
    [ma2 addObject:@"a"];   
   

    NSSortDescriptor *sd2 = [NSSortDescriptor sortDescriptorWithKey:@"self" ascending:YES];

注：self 可以换成model里的变量名

    NSArray *arr2 = [ma2 sortedArrayUsingDescriptors:[NSArray arrayWithObjects:sd2, nil]];
   
    for (NSString *str in arr2) {
        NSLog(@"%@", str);
    }
   
    NSMutableArray *ma3 = [[NSMutableArray alloc] init];
   
    NSMutableDictionary *md1 = [[NSMutableDictionary alloc] init];
    [md1 setObject:@"e" forKey:@"name"];
   
    NSMutableDictionary *md2 = [[NSMutableDictionary alloc] init];
    [md2 setObject:@"d" forKey:@"name"];
   
    NSMutableDictionary *md3 = [[NSMutableDictionary alloc] init];
    [md3 setObject:@"f" forKey:@"name"];
   
    [ma3 addObject:md1];
    [ma3 addObject:md2];
    [ma3 addObject:md3];
   
    [md1 release];
    [md2 release];
    [md3 release];   
   
    NSSortDescriptor *sd3 = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];
    NSArray *arr3 = [ma3 sortedArrayUsingDescriptors:[NSArray arrayWithObjects:sd3, nil]];
   
    for (NSMutableDictionary *md in arr3) {
        NSLog(@"%@", [md objectForKey:@"name"]);
    }
                           
    [ma1 release];
    [ma2 release];
    [ma3 release];