iOS 获取设备唯一标示

http://blog.163.com/l1_jun/blog/static/1438638820155108054177/

原文链接：http://tinymission.com/post/ios-identifierforvendor-frequently-changing

When Apple got rid of access to the UDID for developers in Xcode 5.0, they promised a solution that would be unique for your company identifier and would be constant as long as at least one of your apps was installed
on a device: identifierForVendor.

For the last month, I’ve been struggling with one of my enterprise distribution applications, where device identifiers have been changing frequently on many of my devices. It happens even when the app hasn’t been deleted, but it frequently occurs when the app
version is upgraded, or even at random times. I track access and status by device, so having a reliable device identifier is essential for this project. I started receiving error notifications that device IDs didn’t exist in my database and began to monitor
the situation more closely. I have now recorded several instances of a device ID changing during app usage, where I receive two notifications one minute or less apart containing two different device IDs. I can’t say for sure if this is unique to enterprise
distributions, specific hardware types, specific OS versions, or something else, but I am definitely not imagining it. If you are a developer who needs a way to track access to your app by device, and you can’t control what OS your users are on, you need a
better system. I’ve chosen to capture the identifierForVendor when the app is first installed and store it in the keychain. This has the advantage of persisting even when the app has been deleted, and can be used between apps as well. I came across a great
Keychain wrapper calledUICKeyChainStore and put it into
place. It’s a very simple library to implement and has worked great for my apps.
Add Security.framework to your target
Import the library using either Cocoapods or
just adding the two relevant files to your project
(Optional) Add the Keychain Sharing entitlement to your app target if you want the ability to share keychains between your different apps
Store the device ID to the keychain:

NSString *deviceId = [[UIDevice currentDevice] identifierForVendor] UUIDString];
[UICKeyChainStore setString:deviceId forKey:@"deviceId" service:@"Devices"];

Retrieve the device ID from the keychain:

NSString *deviceId = [UICKeyChainStore stringForKey:@"deviceId" service:@"Devices"];

Updated for iCloud from one of our readers:

There is a risk of setting several device IDs the same if you back up this keychain entry to iCloud. This can happen in two ways:
Through iCloud Keychain (meaning that the keychain would be synced to another one of my devices, and I’d get the same device identifier there as well)
Through backups (the app’s data, including keychain, is saved on backups and can be restored to a new device, thus copying the device identifier)

For the item to be synced with iCloud keychain, I’d need to explicitly set the 

kSecAttrSynchronizable

attribute, so that’s not happening.

Backups are indeed a potential problem, but I found out that you can add the attribute

kSecAttrAccessibleAlwaysThisDeviceOnly

 to prevent this.

Thanks for the feedback and additional input!