NSURLConnection的initWithRequest何时返回nil [英] When does NSURLConnection's initWithRequest return nil

问题描述

有谁知道在初始化 NSURLConnection 的情况下，返回nil而不是创建的连接。文档说它可能但是没有指定何时发生。

Does anyone know in which situations initializing a NSURLConnection returns nil instead of the created connection. The documentation says it's possible but fails to specify when this happens.

有问题的方法/消息：

[[NSURLConnection alloc] initWithRequest：request delegate：self];

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根据 NSURLConnection 类参考：

返回值：URL请求的URL连接。如果无法初始化连接，则返回nil。

Return Value: The URL connection for the URL request. Returns nil if a connection can't be initialized.

URL加载系统编程指南中说明如下：

The URL Loading System Programming Guide says the following:

如果NSURLConnection无法为请求创建连接，则initWithRequest：delegate：返回nil。

If NSURLConnection can’t create a connection for the request, initWithRequest:delegate: returns nil.

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虽然此方法可能返回nil，但我无法想出触发此方法的方案。我尝试了以下方案：

While it's possible that this method returns nil, I'm unable to come up with a scenario which triggers this. I've tried the following scenarios:

• URLRequest 带有空网址： connection：didFailWithError：使用不支持的URL作为错误调用委托方法。


• URLRequest 包含无效的url： connection：didFailWithError：调用委托方法时出现bad URL错误。


• URLRequest ，且不存在url： connection：didFailWithError：调用委托方法时出现找不到指定主机名的服务器。错误。


• 有效请求但没有互联网：连接：didFailWithError：调用委托方法时Internet连接似乎处于脱机状态。错误。


• 无请求：导致崩溃。

• URLRequest with an empty url: connection:didFailWithError: delegate method is called with "unsupported URL" as error.
• URLRequest with invalid url: connection:didFailWithError: delegate method is called with "bad URL" as error.
• URLRequest with nonexistent url: connection:didFailWithError: delegate method is called with "A server with the specified hostname could not be found." as error.
• Valid request but no internet: connection:didFailWithError: delegate method is called with "The Internet connection appears to be offline." as error.
• nil request: causes a crash.

initWithRequest 方法在每个场景中返回一个有效的 NSURLConnection （除了最后一个场景）并调用连接：didFailWithError：有适当的错误。

The initWithRequest method returned a valid NSURLConnection in each scenario (besides the last one) and called the connection:didFailWithError: with an appropriate error.

有没有人能够找出导致nil返回的场景？

Has anybody been able to figure out which scenario does cause nil to be returned?

推荐答案

我猜答案是从不。似乎NSURLConnection返回nil的唯一方法是在[super init]失败。 （[super init]返回nil）但是作为NSURLConnection的超类是NSObject和NSObjects init只返回self（从不为零）

I guess the answer is "Never". Seems only way for NSURLConnection to return nil is failing at [super init]. ([super init] returning nil) But as super class of NSURLConnection is NSObject and NSObjects init just returns self (never nil)

PS：这是IOS SDK 4.0，模拟器，可以在设备上有所不同。

PS: That's for IOS SDK 4.0, on emulator, can be different on device.

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