警告：正在主线程上执行长时间运行的操作。尝试！获取数据（）。迅速

Question

我知道错误来自try! converyPFFile.getData()

如果我不想在后台获取数据，想知道如何消除错误，因为如果我在后台获取数据，则无法将图像附加到数组中。谢谢。

        query.findObjectsInBackgroundWithBlock { (objects: [PFObject]?, error: NSError?) -> Void in
            for object in objects! {
                self.senderArray.append(object.objectForKey("sender") as! String)
                self.messageArray.append(object.objectForKey("message") as? String)
                if object.objectForKey("photo") != nil {
                    if let converyPFFile = object.objectForKey("photo") as? PFFile{
                        let temp = try! converyPFFile.getData()
                        let image = UIImage(data: temp)
                        self.photoArray.append(image)
                    }
                } else {
                    self.photoArray.append(nil)
                }
            }
            // create a chat interface
            if self.senderArray[i] == self.userName {
                if self.messageArray[i] != nil {
                    // using scroll view
                    // create username label
                    // create message text label
                } else { 
                    // using scroll view
                    // create username label
                    // create message image
                    messageImage.image = self.photoArray[i]
                }
                ....

Answer 1

我发现这个警告来自 Parse。您可以通过使用getDataInBackgroundWithBlock 来克服它，然后在该块中附加到您的数组。因此，您的代码变得类似于（未经测试，我认为我的大括号配对错误）：

    query.findObjectsInBackgroundWithBlock { (objects: [PFObject]?, error: NSError?) -> Void in
        for object in objects! {
            self.senderArray.append(object.objectForKey("sender") as! String)
            self.messageArray.append(object.objectForKey("message") as? String)
            if object.objectForKey("photo") != nil {
                if let converyPFFile = object.objectForKey("photo") as? PFFile{
                    converyPFFile.getDataInBackgroundWithBlock { (data: NSData!, error: NSError!) -> Void in
                    let image = UIImage(data: data)
                    self.photoArray.append(image)
                }
            } else {
                self.photoArray.append(nil)
            }
        }
        // create a chat interface
        if self.senderArray[i] == self.userName {
            if self.messageArray[i] != nil {
                // create username label
                // create message text label
            } else { 
                // create username label
                // create message image
                messageImage.image = self.photoArray[i]
            }
            ....

Answer 2

可以在后台执行您的任务，同时仍确保附加到您的照片数组是在主线程上完成的。 您只需将该特定代码分派到主线程即可。 请参阅下面的示例：

    query.findObjectsInBackgroundWithBlock { (objects: [PFObject]?, error: NSError?) -> Void in
        for object in objects! {
            self.senderArray.append(object.objectForKey("sender") as! String)
            self.messageArray.append(object.objectForKey("message") as? String)
            if object.objectForKey("photo") != nil {
                if let converyPFFile = object.objectForKey("photo") as? PFFile{
                    let temp = try! converyPFFile.getData()
                    let image = UIImage(data: temp)
                    // this will cause self.photoArray.append to be executed on the main thread
                    dispatch_async(dispatch_get_main_queue(),{
                        self.photoArray.append(image)
                    })
                }
            } else {
                // this will cause self.photoArray.append to be executed on the main thread
                dispatch_async(dispatch_get_main_queue(),{
                    self.photoArray.append(nil)
                })
            }
        }
        // create a chat interface
        if self.senderArray[i] == self.userName {
            if self.messageArray[i] != nil {
                // create username label
                // create message text label
            } else {
                // create username label
                // create message image
                messageImage.image = self.photoArray[i]
    }