无法使用 NSMetadataquery 和 kMDItemUserTags 获得用户标签的聚光灯搜索结果答案

【问题标题】：Not able to get results for spotlight search for user tags with NSMetadataquery and kMDItemUserTags无法使用 NSMetadataquery 和 kMDItemUserTags 获得用户标签的聚光灯搜索结果
【发布时间】：2017-07-30 13:45:51
【问题描述】：

在尝试向我的控制器添加例程以在用户的计算机上搜索具有指定用户 (Mavericks+) 标记的用户文件后，我束手无策。我遇到了一个搜索将开始的块，但没有返回任何结果并且操作队列为零。

代码如下：

class myController: NSWindowController {

    //define metadataQuery 
    var metadataQuery: NSMetadataQuery!
    var metadataQueryDidUpdateObserver: AnyObject?
    var metadataQueryDidFinishGatheringObserver: AnyObject?

    //initialize notificationsCenter
    let notificationsCenter = NotificationCenter.default

func doSpotlightSearch(){

    //add observers
    notificationsCenter.addObserver(self, selector: "initalGatherComplete:", name: NSNotification.Name.NSMetadataQueryDidFinishGathering, object: nil)
    notificationsCenter.addObserver(self, selector: "batchReturned:", name: NSNotification.Name.NSMetadataQueryDidUpdate, object: nil)


    metadataQuery = NSMetadataQuery()
    metadataQuery.searchScopes = [NSMetadataQueryIndexedLocalComputerScope]
    metadataQuery.predicate = NSPredicate(format: "kMDItemUserTags == 'myTags.testTag'")

    //start search
    metadataQuery.start()

    //test to see if query is up and running
    while metadataQuery.isGathering{
        print(metadataQuery.operationQueue?.operationCount)
        print ("result count: \(metadataQuery.resultCount)")
        sleep(1)
    }

func batchReturned(_ sender: NSNotification) {
    print("Running batchReturned func")

    let resultCounter = metadataQuery.resultCount
    print("Number of results:\(resultCounter)")
    let notificationsCenter = NotificationCenter.default

    notificationsCenter.removeObserver(self, name: NSNotification.Name.NSMetadataQueryDidFinishGathering, object: nil)
}

func initalGatherComplete(_ sender: NSNotification) {
    print("Running initialGatherComplete func")

    metadataQuery.stop()
    let resultCounter = metadataQuery.resultCount
    print("Number of results:\(resultCounter)")
    let notificationsCenter = NotificationCenter.default
    notificationsCenter.removeObserver(self, name: NSNotification.Name.NSMetadataQueryDidFinishGathering, object: nil)
}

当我运行上面的代码时，它显示结果队列为零，结果计数为零。即使我取出 isGathering 循环，batchReturned 和 initialGatherComplete 函数也不会被调用。

我怀疑谓词格式可能存在问题，但是当我使用 mdfind 将查询放入终端时，这可以正常工作。

【问题讨论】：

标签： swift macos tags spotlight nsmetadataquery

【解决方案1】：

来自NSMetadataQuery.start()方法的文档：This method must be called from the receiver’s operationQueue or on the main thread.

如果您没有从主线程调用 start() 方法，您有责任自己创建 OperationQueue 并从那里开始，例如：

// Declare on class-level
private lazy var queryOperationQueue: OperationQueue = {
  let queue = OperationQueue()
  queue.maxConcurrentOperationCount = 1 // restriction for NSMetadataQuery
  return queue
}()


...

func doSpotlightSearch() {
  metadataQuery = NSMetadataQuery()
  metadataQuery.searchScopes = [NSMetadataQueryIndexedLocalComputerScope]
  metadataQuery.predicate = NSPredicate(format: "kMDItemUserTags == 'myTags.testTag'")

  // assign queue to NSMetadataQuery
  metadataQuery.operationQueue = queryOperationQueue

  // run query from its queue
  metadataQuery.operationQueue?.addOperation {
    metadataQuery.start()
  }
}

希望清楚。

【讨论】：