iOS之NSMutableDictionary导致程序崩溃：'NSInternalInconsistencyException'

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"];
}