unity在ios上获取一个永远不变的标记

在Unity中，可以使用Keychain来存储和获取设备的唯一标识符。以下是一些示例代码，可以帮助你在iOS上获取一个永远不变的标记：

using System.Runtime.InteropServices;
using UnityEngine;

public static class DeviceInfo
{
    #if UNITY_IOS
    [DllImport("__Internal")]
    private static extern string _GetDeviceID();
    #endif
 
    public static string GetDeviceID()
    {
        string deviceID = "";
 
        #if UNITY_IOS
        deviceID = _GetDeviceID();
        #endif
 
        if (string.IsNullOrEmpty(deviceID))
        {
            Debug.LogError("Failed to get device ID");
        }
 
        return deviceID;
    }
}

然后，在Objective-C中实现_GetDeviceID()方法：

#import <Foundation/Foundation.h>
#import <Security/Security.h>
#include <sys/sysctl.h>

NSString* GetDeviceID()
{
    NSString *serviceName = [[NSBundle mainBundle] bundleIdentifier];
    NSString *accountName = @"DeviceID";
    NSDictionary *query = @{
                            (__bridge id)kSecClass: (__bridge id)kSecClassGenericPassword,
                            (__bridge id)kSecAttrService: serviceName,
                            (__bridge id)kSecAttrAccount: accountName,
                            (__bridge id)kSecReturnData: @YES
                            };
    CFTypeRef dataTypeRef = NULL;
    OSStatus status = SecItemCopyMatching((__bridge CFDictionaryRef)query, &dataTypeRef);
    if (status == noErr && dataTypeRef != NULL)
    {
        NSData *data = (__bridge NSData *)dataTypeRef;
        NSString *deviceID = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        return deviceID;
    }
    
    NSString *deviceID = [GetUUID() lowercaseString];
    NSData *data = [deviceID dataUsingEncoding:NSUTF8StringEncoding];
    query = @{
              (__bridge id)kSecClass: (__bridge id)kSecClassGenericPassword,
              (__bridge id)kSecAttrService: serviceName,
              (__bridge id)kSecAttrAccount: accountName,
              (__bridge id)kSecValueData: data
              };
    status = SecItemAdd((__bridge CFDictionaryRef)query, NULL);
    if (status != noErr)
    {
        NSLog(@"Failed to save device ID");
    }
    
    return deviceID;
}

NSString* GetUUID()
{
    CFUUIDRef uuidRef = CFUUIDCreate(kCFAllocatorDefault);
    CFStringRef uuidStringRef = CFUUIDCreateString(kCFAllocatorDefault, uuidRef);
    NSString *uuid = (__bridge NSString *)uuidStringRef;
    CFRelease(uuidRef);
    CFRelease(uuidStringRef);
    return uuid;
}

这个方法将使用Keychain来存储设备的唯一标识符。如果设备上没有存储标识符，则会生成一个新的唯一标识符并将其存储在Keychain中。如果设备上已经存在标识符，则直接从Keychain中获取它。这样，即使用户删除并重新安装应用程序，设备的唯一标识符也将保持不变。

请注意，此方法需要在Unity中使用iOS插件来实现。将上述Objective-C代码放入一个名为"DeviceID.m"的文件中，并将其添加到Unity项目的Plugins/iOS目录中即可。