Question

我从Parse导入数据并尝试将其放入页面视图控制器中。查询的代码是正确的，但它没有被调用。它尝试将数组内的对象添加到pageviewcontroller，但这些数组是空的，它们只会在查询后填充。那么如何确保查询运行并首先填充数组？

override func viewDidLoad() {
    super.viewDidLoad()
    testRetrieveInfo()
}

 func retrieveinfo(callback:([String])->Void){

     let query = PFQuery(className: "Animals")
        query.findObjectsInBackgroundWithBlock { (objects:[PFObject]?, error: NSError?) in
                if(error == nil){
                    for object in objects!{     
                        if let importname = object["Name"] as? String{
                            self.name = NSArray(object: importname)
                            print(self.name) //Nothing prints, I also breakpoint and it crashes first, crash location is above in viewDidLoad
                        }
                    }

                }else{
                        print(error)
                }
            }
       }
  }

func testRetrieveInfo(){
    self.retrieveInfo { (results:[String]) -> Void in
        //Setup here the PageViewController
        self.pageViewController.storyboard?.instantiateViewControllerWithIdentifier("PageVC") as? UIPageViewController
        self.pageViewController.dataSource = self
        var startVC = self.viewControllerAtIndex(0) as? Jwasy
        var viewControllers = NSArray(object: startVC!)
        self.pageViewController.setViewControllers(viewControllers as? [UIViewController], direction: .Forward , animated: true, completion: nil)
        self.pageViewController.view.frame = CGRectMake(0, 30, self.view.frame.width, self.view.frame.height)
        self.addChildViewController(self.pageViewController)
        self.view.addSubview(self.pageViewController.view)
        self.pageViewController.didMoveToParentViewController(self)
        print("called")//not printed
    }
}

Answer 1

要在下载数据时收到通知，您有不同的选项（但最基本的是在查询的回调中设置PageViewController）：

0 - 您可以创建一个方法来设置PageViewController并在查询的回调中调用。

1 - 创建自己的回调

func retrieveInfo(callback:([String])->Void){
    //Inside your query callback you're going to call yours
    let query = PFQuery(className: "Animals")
    query.findObjectsInBackgroundWithBlock { (objects:[PFObject]?, error: NSError?) in
        if(error == nil){
            var results:[String] = []
            for object in objects!{     
                 if let importname = object["Name"] as? String{
                     self.results.append(importname)
                 }
            }
            callback(results)
        }else{
            //Can also create a callback for failure 
            print(error)
        }
   }
}

//Used 
func testRetrieveInfo(){
    self.retrieveInfo { (results:[String]) -> Void in
        //Setup here the PageViewController
    }
}

2 - 创建代表

3 - 通知中心

注意：您每次都在循环中重新创建名称数组。你能看一下断点的打印屏幕吗？

如何在实例化pageViewController之前运行查询并填充数组

1 个答案: