IOS NSMutableDictionary setObject setValue

NSMutableDictionary     - (void)setObject:(id) for :(NSstring *)key    當id 為 nil，會出現 crash。    但是，當用setValue 則沒有事情。目前 Dic 用setValue 代替 setObject 構建MutableDictionary，沒有出現什麼大問題 例子： NSMutableDictionary  *dic1 = [NSMutableDictionary dictionaryWithCapacity:1];     [dic1 setObject:@"1" forKey:@"1"];     [dic1 setObject:@"2" forKey:@"2"];     [dic1 setObject:@"" forKey:@"3"];     [dic1 setObject:@"4" forKey:@"4"];         //[dic setObject:nil forKey:@"41"]; wrong         [dic1 setValue:nil forKey:@"5"];         [dic1 setValue:@"6" forKey:@"6"];         [dic1 setValue:[NSDate date] forKey:@"date"];     [dic1 setValue:[NSString string] forKey:@"nil string"];         [dic1 setValue:[NSDictionary dictionaryWithObject:[[UIView alloc] init] forKey:@"View"] forKey:@"複雜非String"];     2013-03-15 14:36:42.089 GuessMovies[5924:c07] {     1 = 1;     2 = 2;     3 = "";     4 = 4;     6 = 6;     date = "2013-03-15 06:35:56 +0000";     "nil string" = "";     "\U590d\U6742\U975eString" =     {         View = "<UIView: 0xa421a10; frame = (0 0; 0 0); layer = <CALayer: 0xa24be80>>";     }; }