Objective - C中無法識別的選擇發送到實例

Question

我收到此錯誤：

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

在這行代碼：

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

keyCounter等於0，這裏是myArray的樣子

我試圖讓baseLineStart的價值，但我磕ep得到上面的錯誤....我該如何解決這個問題？

Answer 1

objectForKey通常用於詞典。

如果您要訪問的屬性，只是引用它：

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

或者用更現代的語法：

NSString *productionItem = myArray[keyCounter].baseLineStart; 

Answer 2

事實是，ProductionCellData做筆記響應此選擇，您應該使用

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

或以這種方式從對象獲取屬性（如果它是公開的）

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

Answer 3

嘗試通過以下方式查找錯誤。

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