Swift:如何根据完成 block 中的结果重新运行函数？

Question

这是一个粗略的示例(我正在处理的实际用例与 PHImageManager 的 requestImageForAsset: 函数的内部有关)，但我正在寻找一种模式，允许您重新运行基于结果在完成 block 中。

Playground 代码:

private func subtractTen (value: Int, completion: (success: Bool, newVal: Int, [NSObject: AnyObject]?) -> Void) -> Int {
  // This is private to represent a black box.
  // In my personal use-case, it's actually a Foundation method
  completion(success: (value - 10 >= 0), newVal: value - 10, nil)

  return value - 10
}

func alwaysPositive (value: Int) -> Int {
  var foo: Int

  foo = subtractTen(value) { success, newVal, _ in

    if success {
      print ("yay")
    } else {
      // I need subtractTen re-run with a new input: newVal
      // and I need the resulting value in the calling function
      // (in this case, "foo")
      print ("re-run subtractTen with newVal, and return the value to the parent function")
    }

    return
  }

  return foo
}

alwaysPositive(10)

您可以使用 1、2、9、10、11 等值运行alwaysPositive，以查看何时显示“重新运行”消息。

对于我想要做的事情有一个通用的 Swift 模式吗？

Answer 1

看看这段代码，也许它会对您正在寻找的内容有所帮助:

override func viewWillAppear(animated: Bool) {
    rerunThis(0, callback: { (number_returned: Int, returned: Bool) in
        println("returned: \(number_returned), \(returned)");

        self.rerunThis(number_returned, callback: { (new_number_returned: Int, returned: Bool) in
            println("new returned: \(new_number_returned), \(returned)");
        });
    });
}

func rerunThis(last_number: Int, callback: ((Int, Bool)->Void)) {
    let new_value: Int = last_number+1;
    var return_this: Bool = false;
    if (new_value <= 1){
        return_this = true;
    }
    callback(new_value, return_this);
}