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# start()

Attempts to start the query.

```
func start() -> Bool
```

## Return Value

<doc://com.apple.documentation/documentation/Swift/true> when successful; otherwise, <doc://com.apple.documentation/documentation/Swift/false>.

  A query may fail to start if it does not specify a [`predicate`](/documentation/Foundation/NSMetadataQuery/predicate)  , or if the query has already been started.

## Discussion

A query can’t be started if the receiver is already running a query or no predicate has been specified.

This method must be called from the receiver’s [`operationQueue`](/documentation/Foundation/NSMetadataQuery/operationQueue) or on the main thread. For example:

```swift
let query: NSMetadataQuery = // Initialize and set up a query
    query.operationQueue?.addOperationWithBlock {
        query.startQuery()
}
```

---

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