这是示例代码:NSDictionary*myDictionary=[NSDictionarydictionary];NSNumber*myNumber=[myDictionaryvalueForKey:@"MyNumber"];NSLog(@"myNumber=%@",myNumber);//outputmyNumber=(null)if(myNumber==nil)NSLog(@"test1myNumber==nil");if(myNumber==NULL)NSLog(@"test2myNumber==NULL");if([myNumberisEqual:[NSNullnull]])