objective-c - ios中存档取消存档，如何处理错误？

Question

我有一个业务对象，我需要更改其属性之一。我尝试获取该属性的字符串表示形式，然后修改它，就像我在下面的代码中尝试的那样

  NSMutableString *mutatingString = [ [ NSMutableString alloc ] init ] ;
  mutatingString = ( NSMutableString * ) [ businessOject valueForKey:@"basicproperty" ] ;
  [ mutatingString appendString:@"Modified" ];

当我热第三行时，我追加了字符串，我得到以下异常:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 
   'Attempt to mutate immutable object with appendString:'

我的代码有什么问题吗？

Answer 1

您不应将 [businessOject valueForKey:@"basicproperty"] 的结果从 NSString* 转换为 NSMutableString*。

NSString* str  =   [businessOject valueForKey:@"basicproperty" ];
NSMutableString *mutatingString = [[NSMutableString alloc ] initWithString:str  ] ;
[mutatingString appendString:@"Modified" ];
[businessOject setValue:mutatingString forKey:@"basicproperty" ]