从后台线程返回函数

Question

My function execution is taking time

    func hasValidValues() -> Bool{
        let leftValue = Double(leftTextValue) ?? 0
        let rightValue = Double(rightTextValue) ?? 0
        switch self.stackViewType {
            let leftValid = self.hasValidValue(min: targetMin, max: targetMax, value: CGFloat(leftValue), unitConversation: true)
            let rightValid = self.hasValidValue(min: 0, max: plusMinusLimit, value: CGFloat(rightValue), unitConversation: true)
            return leftValid && rightValid
}

Now I need to execute this in background thread, and wanted to return so UI thread can access it and I can change UI in another controller.

Can anyone help me on this?

Answer 1

Use DispatchQueue :

DispatchQueue.global().async {
    let result = self.hasValidChanges()
    DispatchQueue.main.async {
        // Use result
    }
}

Answer 2

You can't return value from another tread because each thread has its own stack. So you have to use callback here.

func checkValidValues(completionHandler: @escaping ((Bool) -> Void)) {
    DispatchQueue.global().async { [unowned self] in
        let result = self.hasValidChanges()
        DispatchQueue.main.async {
        completionHandler(result)
    }
}

Answer 3

You could use a dispatch group

var b: Bool = false
let queue = DispatchQueue(label: "myQueue")

let group = DispatchGroup()
group.enter()

DispatchQueue.global().async {
    b = hasValidValues()
    group.leave()
}

group.notify(queue: queue) {
    //use b
}