可在iOS 7和iOS 8上运行的警报

Question

我正在得到dyld:未找到符号:_OBJC_CLASS _ $ _ UIAlertAction当我试图让这个怪物运行时.

我如何弱连接8.0的东西？

var device : UIDevice = UIDevice.currentDevice()!;
var systemVersion = device.systemVersion;
var iosVerion : Float = systemVersion.bridgeToObjectiveC().floatValue;
if(iosVerion < 8.0) {
    let alert = UIAlertView()
    alert.title = "Noop"
    alert.message = "Nothing to verify"
    alert.addButtonWithTitle("Click")
    alert.show()
} else {
    var alert : UIAlertController? = UIAlertController(title: "Noop", message: "Nothing to verify", preferredStyle: UIAlertControllerStyle.Alert)
    if alert {
        let actionStyle : UIAlertActionStyle? = UIAlertActionStyle.Default;
        var alertAction : UIAlertAction? = UIAlertAction(title: "Click", style: actionStyle!, handler: nil)
        if(alertAction) {
            alert!.addAction(alertAction)
            self.presentViewController(alert, animated: true, completion: nil)
        }
    }
}
return;

已解决:UIKit必须标记为Optional而不是Required.简化版现在是:

var device : UIDevice = UIDevice.currentDevice()!;
var systemVersion = device.systemVersion;
var iosVerion : Float = systemVersion.bridgeToObjectiveC().floatValue;
if(iosVerion < 8.0) {
    let alert = UIAlertView()
    alert.title = "Noop"
    alert.message = "Nothing to verify"
    alert.addButtonWithTitle("Click")
    alert.show()
} else {
    var alert : UIAlertController = UIAlertController(title: "Noop", message: "Nothing to verify", preferredStyle: UIAlertControllerStyle.Alert)
    alert.addAction(UIAlertAction(title: "Click", style:.Default, handler: nil))
    self.presentViewController(alert, animated: true, completion: nil)
}

Answer 1

• 在项目构建阶段的"Link Binary With Libraries"部分中明确添加UIKit.

• 您可以像这样测试UIAlertController的存在:

  if NSClassFromString("UIAlertController") != nil {
      // Use it
  } else {
      // Fall back
  }
  

• 我写了一个适用于iOS 7和iOS 8的包装器.你可以在这里找到它.它需要一个视图控制器,后跟一堆可选参数和任意数量的按钮:

  showAlert(self, style: .ActionSheet, sourceView: cell, completion: {
      tableView.deselectRowAtIndexPath(indexPath, animated: true)
  },
      (.Default, "Send clipboard", {
          if someCondition {
              // completion must be specified because of a Swift bug (rdar://18041904)
              showAlert(self, title: "Nothing to send", message: "The clipboard is empty.", completion: nil,
                  (.Cancel, "OK", nil)
              )
          }
      }),
      (.Cancel, "Cancel", nil)
  )