Objective - C中无法识别的选择发送到实例

Question

我收到此错误：

'-[ProductionCellData objectForKey:]: unrecognized selector sent to instance 0x14dca5d0' 

在这行代码：

NSString *productionItem = [[myArray objectAtIndex:keyCounter] objectForKey:@"baseLineStart"]; 

keyCounter等于0，这里是myArray的样子

我试图让baseLineStart的价值，但我磕ep得到上面的错误....我该如何解决这个问题？

Answer 1

objectForKey通常用于词典。

如果您要访问的属性，只是引用它：

NSString *productionItem = [myArray objectAtIndex:keyCounter].baseLineStart; 

或者用更现代的语法：

NSString *productionItem = myArray[keyCounter].baseLineStart; 

Answer 2

事实是，ProductionCellData做笔记响应此选择，您应该使用

- (nullable id)valueForKey:(NSString *)key; 

或以这种方式从对象获取属性（如果它是公开的）

NSString *productionItem = [[myArray objectAtIndex:keyCounter] baseLineStart]; 

Answer 3

尝试通过以下方式查找错误。

NSDictionary *dic = [myArray objectAtIndex:keyCounter]; 
NSLog(@"dic:%@",dic); 
NSString *productionItem = [dic objectForKey:@"baseLineStart"]; 

//1. observe the dic object has "baseLineStart" key. if not found write the correct one. 
//2. objeserve what type of value returns "[myArray objectAtIndex:keyCounter]". it may not NSDictionary which may resoan of crash