核心数据 - 希望出现错误，获取异常 [英] Core Data - Hoping for errors, getting exceptions

问题描述

我正在使用Core Data开发一个iPhone应用程序，ahev注意到当我期望和错误时，我得到异常，这是一个例子：

I am developing an iPhone app using Core Data and ahev noticed that I get exceptions when I would expect and error, this is an example:

NSError *error;

// exception here if edited attribute name todoText in modeller and generated new database with that new name in it(ie clearing the iphone), ie tring to access a field not in the database

@try {

   NSMutableArray *mutableFetchResults = [[todoListManagedObjectContext   executeFetchRequest:request error:&error] mutableCopy];

   //seems like vars declaered inside a try is only known inside it, so process here

   if (mutableFetchResults == nil) { // nil = error

      // Handle the error.

如在注释中看到的，我没有得到一个错误，试图访问一个不存在的字段。 ...为什么不使用错误返回系统为此？

As seen in the comments I don't get an error for trying to access a non existing field....why not just use the error return system for this?

我想我的问题是，什么是错误和例外，我真的需要测试这样吗？

I guess my question is, what are errors and exceptions for, and do I really need to test for both like this?

Rgds
PM

Rgds PM

推荐答案

在Cocoa中，异常通常意味着程序员错误，所以它建议你传递一个无效的参数。试图访问不在数据库中的字段看起来像这样的情况;它不是一个错误的东西的错误，它是一个你做错了错误。

What exception are you getting? Throughout Cocoa, exceptions generally mean programmer error so it suggests you're passing a parameter which is not valid. Trying to access a field which isn't in the database seems like such a situation; it's not a "something went wrong" error, it's a "you did something wrong" error.

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