Xcode从8升级至9.3.1遇'id<NSCopying>'字典读取错误求助

这个问题我之前帮不少升级Xcode的开发者排查过，本质是Xcode 9.3.1搭载的Clang编译器对静态类型检查变得更严格了：你的options变量类型是id<NSCopying>，它仅表示对象实现了NSCopying协议，但编译器无法确定它就是NSDictionary（毕竟NSString、NSArray等很多类都实现了该协议），因此不认可字典下标[]的访问语法——只有NSDictionary/NSMutableDictionary才有这个下标方法，这就是报错的核心原因。

下面给你两种直接可行的解决方向：

方案1：强制类型转换明确字典类型 #

在访问options时，直接将其转换为NSDictionary*，让编译器明确知道这是一个字典实例。你可以选择逐行转换，或者先声明局部变量统一转换（后者更整洁）：

逐行转换示例 #

// Normalize the blending mode to use for the key. 
id src = (((NSDictionary*)options)[CCBlendFuncSrcColor] ?: @(GL_ONE));
id dst = (((NSDictionary*)options)[CCBlendFuncDstColor] ?: @(GL_ZERO));
id equation = (((NSDictionary*)options)[CCBlendEquationColor] ?: @(GL_FUNC_ADD));

NSDictionary *normalized = @{
    CCBlendFuncSrcColor: src,
    CCBlendFuncDstColor: dst,
    CCBlendEquationColor: equation,
    // Assume they meant non-separate blending if they didn't fill in the keys. 
    CCBlendFuncSrcAlpha: (((NSDictionary*)options)[CCBlendFuncSrcAlpha] ?: src),
    CCBlendFuncDstAlpha: (((NSDictionary*)options)[CCBlendFuncDstAlpha] ?: dst),
    CCBlendEquationAlpha: (((NSDictionary*)options)[CCBlendEquationAlpha] ?: equation),
};

局部变量统一转换示例 #

NSDictionary *optionsDict = (NSDictionary*)options;
id src = (optionsDict[CCBlendFuncSrcColor] ?: @(GL_ONE));
id dst = (optionsDict[CCBlendFuncDstColor] ?: @(GL_ZERO));
id equation = (optionsDict[CCBlendEquationColor] ?: @(GL_FUNC_ADD));

NSDictionary *normalized = @{
    CCBlendFuncSrcColor: src,
    CCBlendFuncDstColor: dst,
    CCBlendEquationColor: equation,
    CCBlendFuncSrcAlpha: (optionsDict[CCBlendFuncSrcAlpha] ?: src),
    CCBlendFuncDstAlpha: (optionsDict[CCBlendFuncDstAlpha] ?: dst),
    CCBlendEquationAlpha: (optionsDict[CCBlendEquationAlpha] ?: equation),
};

方案2：用objectForKey:替代下标访问 #

字典的objectForKey:是经典实例方法，id类型可以直接调用该方法（编译器不会报错），不过要注意：运行时如果options不是NSDictionary实例会崩溃，所以你要确保传入的options确实是字典：

// Normalize the blending mode to use for the key. 
id src = ([options objectForKey:CCBlendFuncSrcColor] ?: @(GL_ONE));
id dst = ([options objectForKey:CCBlendFuncDstColor] ?: @(GL_ZERO));
id equation = ([options objectForKey:CCBlendEquationColor] ?: @(GL_FUNC_ADD));

NSDictionary *normalized = @{
    CCBlendFuncSrcColor: src,
    CCBlendFuncDstColor: dst,
    CCBlendEquationColor: equation,
    // Assume they meant non-separate blending if they didn't fill in the keys. 
    CCBlendFuncSrcAlpha: ([options objectForKey:CCBlendFuncSrcAlpha] ?: src),
    CCBlendFuncDstAlpha: ([options objectForKey:CCBlendFuncDstAlpha] ?: dst),
    CCBlendEquationAlpha: ([options objectForKey:CCBlendEquationAlpha] ?: equation),
};

额外优化建议 #

如果options参数的定义权限在你手里，建议直接把它的类型从id<NSCopying>改成NSDictionary*（或者NSDictionary<NSCopying, id>*，如果键需要支持拷贝），从根源上避免这类类型检查错误，代码可读性也会更高。

内容的提问来源于stack exchange，提问作者BTVC