如何批量访问iOS联系人？

Question

我正在尝试在Xamarin.iOS中实现联系人读取器，该读取器试图遍历所有CNContactStore容器中的iOS联系人。 除了将所有联系人加载到内存中之外，我还需要逐批迭代联系人结果集（分页联系人）。 但是，我在SO中看到的所有示例都首先将几乎所有联系人加载到内存中。

即， 这个问题有大量类似的例子，可以一次读取所有联系人。 尽管这些示例具有逐个迭代的逻辑，但对我来说，如何跳过N个并接下N个联系人，而又不从下一个呼叫的开头迭代（至少对我来说看起来不太理想），这对我来说并不明显。

苹果自己的文档阅读

When fetching all contacts and caching the results, first fetch all contacts identifiers, then fetch batches of detailed contacts by identifiers as required

我能够使用其SDK中提供的基于游标的方法轻松地针对Android执行此操作。 iOS完全可以吗？ 如果不是，我们如何处理大量的联系（例如2000年以上的联系，等等）。 我不介意举个例子。 我应该能够将它们转换为Xamarin。

提前致谢。

Answer 1

这是我采用的方法，但要满足我的要求，即不允许持久联系，而只能保留活动内存。 不是说这是正确的方法，而是先获取所有标识符，然后根据需要懒惰地获取特定联系人的所有键，确实提高了性能。 当联系人不存在时，它还避免执行查找。 我也尝试使用NSCache而不是字典，但是当我需要遍历缓存时遇到了问题。

我截断了与该主题无关的功能，但希望仍能传达出这种方法。

import Contacts

extension CNContactStore {

    // Used to seed a Contact Cache with all identifiers
    func getAllIdentifiers() -> [String: CNContact]{

        // keys to fetch from store
        let minimumKeys: [CNKeyDescriptor] = [
            CNContactPhoneNumbersKey as CNKeyDescriptor,
            CNContactIdentifierKey as CNKeyDescriptor
        ]

        // contact request
        let request = CNContactFetchRequest(keysToFetch: minimumKeys)

        // dictionary to hold results, phone number as key
        var results: [String: CNContact] = [:]

        do {
            try enumerateContacts(with: request) { contact, stop in

                for phone in contact.phoneNumbers {
                    let phoneNumberString = phone.value.stringValue
                    results[phoneNumberString] = contact
                }
            }
        } catch let enumerateError {
            print(enumerateError.localizedDescription)
        }

        return results
    }

    // retreive a contact using an identifier
    // fetch keys lists any CNContact Keys you need
    func get(withIdentifier identifier: String, keysToFetch: [CNKeyDescriptor]) -> CNContact? {

        var result: CNContact?
        do {
            result = try unifiedContact(withIdentifier: identifier, keysToFetch: keysToFetch)
        } catch {
            print(error)
        }

        return result
    }
}

final class ContactsCache {

    static let shared = ContactsCache()

    private var cache : [String : ContactCacheItem] = [:]

    init() {

        self.initializeCache()  // calls CNContactStore().getAllIdentifiers() and loads into cache

        NotificationCenter.default.addObserver(self, selector: #selector(contactsAppUpdated), name: .CNContactStoreDidChange, object: nil)
    }

    private func initializeCache() {

        DispatchQueue.global(qos: .background).async {

            let seed = CNContactStore.getAllIdentifiers()

            for (number, contact) in seed{

                let item = ContactCacheItem.init(contact: contact, phoneNumber: number )
                self.cache[number] = item
            }
        }
    }

    // if the contact is in cache, return immediately, else fetch and execute completion when finished. This is bit wonky to both return value and execute completion, but goal was to reduce visible cell async update as much as possible
    public func contact(for phoneNumber: String, completion: @escaping (CNContact?) -> Void) -> CNContact?{

        if !initialized {   // the cache has not finished seeding, queue request

            queueRequest(phoneNumber: phoneNumber, completion: completion)  // save request to be executed as soon as seeding completes
            return nil
        }

        // item is in cache
        if let existingItem = getCachedContact(for: phoneNumber) {

            // is it being looked up
            if existingItem.lookupInProgress(){
                existingItem.addCompletion(completion: completion)
            }
            // is it stale or has it never been looked up
            else if existingItem.shouldPerformLookup(){

                existingItem.addCompletion(completion: completion)
                refreshCacheItem( existingItem )
            }
            // its current, return it
            return existingItem.contact
        }

        // item is not in cache
        completion(nil)
        return nil
    }

    private func getCachedContact(for number: String) -> ContactCacheItem?  {
        return self.cache.first(where: { (key, _) in key.contains( number) })?.value
    }


    // during the async initialize/seeding of the cache, requests may come in from app, so they are temporarily 'queued'
    private func queueRequest(phoneNumber: String, completion: @escaping (CNContact?) -> Void){..}
    // upon async initialize/seeding completion, queued requests can be executed
    private func executeQueuedRequests() {..}
    // if app receives notification of update to user contacts, refresh cache
    @objc func contactsAppUpdated(_ notification: Notification) {..}
    // if a contact has gone stale or never been fetched, perform the fetch
    private func refreshCacheItem(_ item: ContactCacheItem){..}
    // if app receives memory warning, dump data
    func clearCaches() {..}
}

class ContactCacheItem : NSObject {

    var contact: CNContact? = nil
    var lookupAttempted : Date?  // used to determine when last lookup started
    var lookupCompleted : Date?  // used to determien when last successful looup completed
    var phoneNumber: String     //the number used to look this item up
    private var callBacks = ContactLookupCompletion()  //used to keep completion blocks for lookups in progress, in case multilpe callers want the same contact info

    init(contact: CNContact?, phoneNumber: String){..}
    func updateContact(contact: CNContact?){..}  // when a contact is fetched from store, update it here
    func lookupInProgress() -> Bool {..}
    func shouldPerformLookup() -> Bool {..}
    func hasCallBacks() -> Bool {..}
    func addCompletion(completion: @escaping (CNContact?) -> Void){..}
}