Question

我现在有一个观察句柄，可以检查添加新频道的时间。我希望它是一个带有按钮的observeSingleEvent，当用户点击它时会重新加载频道。 observeSingleEvent正常工作。这是代码：

private func observeChannels() {
    channelRefHandle = channelRef.observe(.childAdded, with: { (snapshot) -> Void in
        self.playersInChannnel.append("\(snapshot.childrenCount)")
        let channelData = snapshot.value as! Dictionary<String, AnyObject>
        let id = snapshot.key
        if let name = channelData["name"] as! String!, name.characters.count > 0 {
            self.channels.append(Channel(id: id, name: name))
            self.tableView.reloadData()
        } else {
            print("Error! Could not decode channel data")
        }
    })
}

我现在尝试将它转换为observeSingleEvent，把打印说错误，无法解码通道数据。这是我的代码：

func reloadChannels()
{
    channelRef.observeSingleEvent(of: .value, with: { (snapshot) -> Void in
        self.playersInChannnel.append("\(snapshot.childrenCount)")
        let channelData = snapshot.value as! Dictionary<String, AnyObject>
        let id = snapshot.key
        if let name = channelData["name"] as! String!, name.characters.count > 0 {
            self.channels.append(Channel(id: id, name: name))
            self.tableView.reloadData()
        } else {
            print("Error! Could not decode channel data")
        }
    })
}

这段代码有什么问题？这是来自observeSingleEvent的快照的打印：

Snap (channels) {
    "-Ke3g8tLH9A-_iTVjQhq" =     {
        "-Ke3g8tO2XPCbyIjP4Op" =         {
            PictureVersion = "";
            userID = keVlTMUXyRViUsTVjTnKdvZs7mg1;
            username = pietje;
        };
        name = test;
    };
    "-Ke3gFbijlcQGuJXe42L" =     {
        "-Ke3gFbjsEgpA3wjM1Jv" =         {
            PictureVersion = "";
            userID = keVlTMUXyRViUsTVjTnKdvZs7mg1;
            username = pietje;
        };
        name = test2;
    };
}
Error! Could not decode channel data

同样，触发observeChannels（）显示没有错误。谢谢。

Answer 1

您没有从observe更改为observeSingleEvent，您也从观察.childAdded切换到观察.value。由于您现在正在侦听.value，这意味着您获得的快照一次包含所有子节点（即使只有一个匹配的子节点））。

因此，您需要遍历快照的子项，以获取之前的频道数据：

func reloadChannels()
{
    channelRef.observeSingleEvent(of: .value, with: { (snapshot) -> Void in
        self.playersInChannnel.append("\(snapshot.childrenCount)")
        for channelSnap in snapshot.children {
            let channelData = (channelSnap as! FIRDataSnapshot).value as! Dictionary<String, AnyObject>
            let id = (channelSnap as! FIRDataSnapshot).key

            if let name = channelData["name"] as! String!, name.characters.count > 0 {
                self.channels.append(Channel(id: id, name: name))
                self.tableView.reloadData()
            } else {
                print("Error! Could not decode channel data")
            }
        }
    })
}

有关如何循环快照子项的更多信息，请参阅此问题的答案：Iterate over snapshot children in Swift (Firebase)

将观察结果转换为Firebase

1 个答案: