问题描述

我正在处理我的应用程序中的错误，我正在研究使用 NSError.我对如何使用它以及如何填充它感到有些困惑.

I am working on catching errors in my app, and I am looking into using NSError. I am slightly confused about how to use it, and how to populate it.

有人可以提供一个关于我如何填充然后使用 NSError 的示例吗?

Could someone provide an example on how I populate then use NSError?

推荐答案

好吧，我通常做的是让我的可能在运行时出错的方法引用 NSError 指针.如果该方法确实出了问题，我可以使用错误数据填充 NSError 引用并从该方法返回 nil.

Well, what I usually do is have my methods that could error-out at runtime take a reference to a NSError pointer. If something does indeed go wrong in that method, I can populate the NSError reference with error data and return nil from the method.

例子:

- (id) endWorldHunger:(id)largeAmountsOfMonies error:(NSError**)error {
    // begin feeding the world's children...
    // it's all going well until....
    if (ohNoImOutOfMonies) {
        // sad, we can't solve world hunger, but we can let people know what went wrong!
        // init dictionary to be used to populate error object
        NSMutableDictionary* details = [NSMutableDictionary dictionary];
        [details setValue:@"ran out of money" forKey:NSLocalizedDescriptionKey];
        // populate the error object with the details
        *error = [NSError errorWithDomain:@"world" code:200 userInfo:details];
        // we couldn't feed the world's children...return nil..sniffle...sniffle
        return nil;
    }
    // wohoo! We fed the world's children. The world is now in lots of debt. But who cares? 
    return YES;
}

然后我们可以使用这样的方法.除非方法返回 nil，否则不要费心检查错误对象:

We can then use the method like this. Don't even bother to inspect the error object unless the method returns nil:

// initialize NSError object
NSError* error = nil;
// try to feed the world
id yayOrNay = [self endWorldHunger:smallAmountsOfMonies error:&error];
if (!yayOrNay) {
   // inspect error
   NSLog(@"%@", [error localizedDescription]);
}
// otherwise the world has been fed. Wow, your code must rock.

我们能够访问错误的 localizedDescription，因为我们为 NSLocalizedDescriptionKey 设置了一个值.

We were able to access the error's localizedDescription because we set a value for NSLocalizedDescriptionKey.

了解更多信息的最佳位置是 Apple 的文档.确实不错.

The best place for more information is Apple's documentation. It really is good.

可可是我的女朋友.

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