DevTut

# Chain Blocks in a Queue (with MKBlockQueue)

MKBlockQueue allows you to create a chain of blocks and execute them one after the other in a queue. Compared with NSOperation, with MKBlockQueue you decide yourself when a block is complete and when you want the queue to continue. You can also pass data from one block to the next.

https://github.com/MKGitHub/MKBlockQueue (opens new window)

# Example Code

enter image description here (opens new window)

// create the dictionary that will be sent to the blocks
var myDictionary:Dictionary<String, Any> = Dictionary<String, Any>()
myDictionary["InitialKey"] = "InitialValue"

// create block queue
let myBlockQueue:MKBlockQueue = MKBlockQueue()

// block 1
let b1:MKBlockQueueBlockType =
{
    (blockQueueObserver:MKBlockQueueObserver, dictionary:inout Dictionary<String, Any>) in

    print("Block 1 started with dictionary: \(dictionary)")
    dictionary["Block1Key"] = "Block1Value"

    // tell this block is now completed
    blockQueueObserver.blockCompleted(with:&dictionary)

}

// block 2
let b2:MKBlockQueueBlockType =
{
    (blockQueueObserver:MKBlockQueueObserver, dictionary:inout Dictionary<String, Any>) in

    var copyOfDictionary:Dictionary<String, Any> = dictionary

    // test calling on main thread, async, with delay
    DispatchQueue.main.asyncAfter(deadline:(.now() + .seconds(1)), execute:
    {
        print("Block 2 started with dictionary: \(copyOfDictionary)")

        copyOfDictionary["Block2Key"] = "Block2Value"

        // tell this block is now completed
        blockQueueObserver.blockCompleted(with:&copyOfDictionary)
    })
}

// block 3
let b3:MKBlockQueueBlockType =
{
    (blockQueueObserver:MKBlockQueueObserver, dictionary:inout Dictionary<String, Any>) in

    var copyOfDictionary:Dictionary<String, Any> = dictionary

    // test calling on global background queue, async, with delay
    DispatchQueue.global(qos:.background).asyncAfter(deadline:(.now() + .seconds(1)), execute:
    {
        print("Block 3 started with dictionary: \(copyOfDictionary)")

        copyOfDictionary["Block3Key"] = "Block3Value"

        // tell this block is now completed
        blockQueueObserver.blockCompleted(with:&copyOfDictionary)
    })
}

// add blocks to the queue
myBlockQueue.addBlock(b1)
myBlockQueue.addBlock(b2)
myBlockQueue.addBlock(b3)

// add queue completion block for the queue
myBlockQueue.queueCompletedBlock(
{
    (dictionary:Dictionary<String, Any>) in
    print("Queue completed with dictionary: \(dictionary)")
})

// run queue
print("Queue starting with dictionary: \(myDictionary)")
myBlockQueue.run(with:&myDictionary)

← Simulator →