遍歷字典遍歷的是key而不是value!!!

最近項目中需要遍歷字典篩選有用信息,在遍歷時遇到一些崩潰,猛然醒悟,雖不值一提,可也是個知識點,記錄一下.

    NSDictionary * dic = @{@"student":@[@"jim"], @"score":@[@"80"], @"ages":@[@"18", @"20", @"24"]};
    for (id string in dic) {
        NSLog(@"string = %@", string);
    }

結果爲:

 string = score
 string = ages
 string = student

二如果你直接用了value的值

    NSDictionary * dic = @{@"student":@[@"jim"], @"score":@[@"80"], @"ages":@[@"18", @"20", @"24"]};
    for (id string in dic) {
        NSLog(@"string = %@", string[0]);
    }

則會拋出異常:
-[__NSCFConstantString objectAtIndexedSubscript:]: unrecognized selector sent to instance 0x335a4c
意思是說本該是字符串的對象,卻調用objectAtIndex方法,拋出異常.正確的方法是:

    for (id string in dic) {
        id value = dic[string];
        NSLog(@"value = %@", value);
    }