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.
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