Question

NSDictionary *dict = @{@"key": @"value"};
NSData *data = [NSJSONSerialization dataWithJSONObject:dict options:0 error:nil];
NSError *error;
NSDictionary *dict1 = [NSJSONSerialization JSONObjectWithData:data  
    options:NSJSONReadingMutableLeaves  error:&error];
NSMutableString *ms =  [dict1 objectForKey:@"key"];
ms.string = @"ss";

我从上面的代码中得到了一个例外

由于未捕获的异常'NSInvalidArgumentException'而终止应用程序，原因：'尝试使用setString改变不可变对象：'

有什么问题？

Answer 1

我刚遇到这个问题，确实很烦人。

我开发了一个解决方法，在NSMutableArray和NSMutableDictionary上添加了两个，它们解析整个JSON树并用其可变相对替换每个叶子事件（如果它符合NSMutableCopying协议）。

以下是实施：

@implementation NSMutableArray (mutableLeavesAddition)

- (void)setLeavesMutable {
    for (int i=0; i<[self count]; i++) {
        NSObject *element = self[i];
        if ([element isKindOfClass:NSMutableDictionary.class] || [element isKindOfClass:NSMutableArray.class]) {
            [(NSMutableDictionary*)element setLeavesMutable];
        } else if ([element.class conformsToProtocol:@protocol(NSMutableCopying)]) {
            self[i] = [element mutableCopy];
        }
    }
}

@end

@implementation NSMutableDictionary (mutableLeavesAddition)

- (void)setLeavesMutable {
    for (NSString *key in [self allKeys]) {
        NSObject *element = self[key];
        if ([element isKindOfClass:NSMutableDictionary.class] || [element isKindOfClass:NSMutableArray.class]) {
            [(NSMutableDictionary*)element setLeavesMutable];
        } else if ([element.class conformsToProtocol:@protocol(NSMutableCopying)]) {
            self[key] = [element mutableCopy];
        }
    }
}

@end

注意：它仅在您在JSON解析期间选择NSJSONReadingMutableContainers时才有效。

NSJSONReadingMutableLeaves选项不起作用

1 个答案: