[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object 错误

使用NSMutableDictionary时，如果操作不当，有可能会引起程序崩溃。示例代码：

NSString *result = @"{\"username\”:\”aaa\”,\"phone\":\"15666666666\",\"bankcount\":\"98765432112345678\"}";  
NSData *data = [result dataUsingEncoding:NSUTF8StringEncoding];  
NSMutableDictionary *info = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:nil];  
if (info) {  
    NSString *username = [Utils UrlDecode: info[@"username"]];  
    [info  setObject:username forKey:@"username"];  
}  

执行上述代码后报错：

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object'  

出错原因在于：

[NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:nil];

返回的结果是immutable对象，不能直接对immutable进行赋值操作，否则会报错。

修改后代码：

NSString *result = @"{\"username\”:\”aaa\”,\"phone\":\"15666666666\",\"bankcount\":\"98765432112345678\"}";  
NSData *data = [result dataUsingEncoding:NSUTF8StringEncoding];  
//－－－－将immutable转换为mutable－－－－  
NSMutableDictionary *temp = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:nil];  
NSMutableDictionary *info = [NSMutableDictionary dictionaryWithDictionary:temp];  
//－－－－－－－－－－－－－－－－－－－－－－  
if (info) {  
    NSString *username = [Utils UrlDecode:info[@"username"]];  
    [info  setObject:username forKey:@"username"];  
} 

NSMutableDictionary *dic = [getDefaults valueForKey:@"loginInfo"];
[dic2  setObject:tf1.text forKey:@"phone"];

报错:

'-[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object

修改:

NSMutableDictionary *dic = (NSMutableDictionary *)[getDefaults valueForKey:@"loginInfo"];
NSMutableDictionary *dic2 = [NSMutableDictionary dictionaryWithDictionary:dic];
[dic2  setObject:tf1.text forKey:@"phone"];