brentsimmons · April 8, 2016 17:35 · Apr 8, 2016
diff --git a/gist.swift b/gist.swift
@@ -0,0 +1,139 @@
+// This is the traditional version of the RxSwift-based gist posted here:
+// https://gist.github.com/cliss/51cb740b14f3cd56ba1d11f2a9a6ba02
+// This won’t compile and it surely has errors.
+// (The same may be true as the original.)
+// Some things are obviously omitted.
+// It's meant as illustrative rather than as actual running code.
+//
+// The problem being solved:
+// There is a text field. When you type in it, all changes are coalesced
+// for 0.3 seconds, and then an HTTP call is made, and a table is updated
+// with results.
+// Also: there's a Refresh button, and tapping the Refresh button
+// runs that same HTTP call and updates the table with results.
+// Whenever there's an existing HTTP call, and a new one has been triggered,
+// the existing HTTP call should be canceled.
+
+struct Result {
+    let text: String
+    let someOtherThing: String
+}
+
+typealias FetcherCallback = (result: Result?, error: NSError?) -> Void
+
+class Fetcher {
+
+    let task: NSURLSessionDataTask
+
+    init(query: String, callback: FetcherCallback) {
+
+        //Assume the url was created based on the query. And that myURLSession came from somewhere.
+        self.task = myURLSession.dataTaskWithURL(url) { data, response, error in {
+
+            if let error = error {
+                callback(nil, error)
+                return
+            }
+            let results: [Result] = something //make results from the data; obvious omission for the sake of argument
+            callback(results, nil)
+            }
+        }
+
+        self.task.resume()
+    }
+
+    func cancel() {
+        task.cancel()
+    }
+}
+
+class ViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
+
+    private weak var tableView: UITableView!
+    private weak var textField: UITextField!
+    private var fetchTimer: NSTimer?
+    private var fetcher: Fetcher?
+
+    private var results = [String]() {
+        didSet {
+            tableView.reloadData()
+        }
+    }
+
+    private var currentText = "" {
+        didSet {
+            if currentText.count < 4 {
+                invalidateFetchTimer()
+            }
+            else {
+                resetFetchTimer()
+            }
+        }
+    }
+
+    deinit {
+
+        invalidateFetchTimer()
+        cancelExistingFetch()
+    }
+
+    override func viewDidLoad() {
+
+        textField.delegate = self
+    }
+
+    func textDidChange(sender: AnyObject) {
+
+        if currentText != textField.stringValue {
+            currentText = textField.stringValue
+        }
+    }
+
+    private func invalidateFetchTimer() {
+
+        if let timer = fetchTimer where fetchTimer.isValid {
+            timer.invalidate()
+        }
+        fetchTimer = nil
+    }
+
+    private func resetFetchTimer() {
+
+        invalidateFetchTimer()
+        fetchTimer = NSTimer(timeInterval: 0.3, target: self, selector: #selector(fetchTimerDidFire(_:)), userInfo: nil, repeats: false)
+    }
+
+    dynamic func fetchTimerDidFire(sender: AnyObject) {
+
+        runFetch()
+    }
+
+    private func cancelExistingFetch() {
+
+        if let existingFetcher = fetcher {
+            existingFetcher.cancel()
+        }
+        fetcher = nil
+    }
+
+    private func runFetch() {
+
+        invalidateFetchTimer()
+        cancelExistingFetch()
+
+        fetcher = Fetcher(text: currentText) { result, error in
+            if let error = error {
+                //Handle it.
+            }
+            else {
+                self.results = result.map { oneResult in return oneResult.text }
+            }
+        }
+    }
+
+    @IBAction func refresh(sender: AnyObject) {
+
+        runFetch()
+    }
+}
+
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