[英]Async Await operation blocking UI on return from another Frame
我是C#和UWP的新手,這是一項任務,我的交稿時間很緊,所以還沒有時間完全弄清楚問題,因此請原諒。
我有以下代碼,該代碼通過創建AMQP連接並以恆定的while循環從Azure IOT集線器接收消息來工作。
有適當的問題分配,但主要的問題是當我從訪問另一頁面返回時,GUI停止更新文本字段。
實際上,它確實從OnNavigatedTo更新了它們,但是方法Receive Messages停止更新它們,但是在輸出窗口中,我可以看到debug.write正在接收消息,只是不更新文本字段。
我想我需要在單獨的線程上運行while循環,但我認為下面沒有做過,我已經讀過Task.Run等,並嘗試了各種方法,但無法弄清楚。
public MainPage()
{
this.InitializeComponent();
if (receivedStarted != 1)
Receive();
}
private async void Receive()
{
await ReceiveMessages("1");
await ReceiveMessages("0");
}
/// <summary>
/// On Navigated to function from other pages
/// </summary>
/// <param name="e"></param>
protected override void OnNavigatedTo(NavigationEventArgs e)
{
Counter.Text = parsedCounter;
TimeText.Text = "The last activity was at " + parsedTime;
Contact_1.Content = ContactAddPopUp.contact[0, 0];
Contact_2.Content = ContactAddPopUp.contact[1, 0];
Contact_3.Content = ContactAddPopUp.contact[2, 0];
if (Settings.timeChanged == true)
{
if (DelayTimer != null)
{
DelayTimer.Cancel();
Timer();
}
}
}
/// <summary>
/// Receive messages from specified azure iothub on specified partition. The MessageManager parses the received message and displays it accordingly
/// </summary>
/// <param name="partition"></param>
/// <returns></returns>
public async Task ReceiveMessages(string partition)
{
DateTime offset;
offset = DateTime.UtcNow - TimeSpan.FromMinutes(1);
String primaryKey = "fghkfwhihelfihefjw;ojwef";
String sharedAccessPolicy = "iothubowner";
//String hubName = "RaspberryPirSensor";
String deviceName = "PIRSensor";
String eventHubEntity = "iothub-ehub-raspberryp-70680-20f0331ccb";
string port = "iakugfdkjhkjhaflhlkhalkfhse.servicebus.windows.net";
Address address = new Address(port, 5671, sharedAccessPolicy, primaryKey, "/", "amqps");
Connection connection = await Connection.Factory.CreateAsync(address);
Session session = new Session(connection);
string totalMilliseconds = ((long)(offset - new DateTime(StartOfEpoch, DateTimeKind.Utc)).TotalMilliseconds).ToString();
Map filters = new Map();
filters.Add(new Amqp.Types.Symbol("apache.org:selector-filter:string"),
new DescribedValue(
new Amqp.Types.Symbol("apache.org:selector-filter:string"),
"amqp.annotation.x-opt-enqueuedtimeutc > " + totalMilliseconds + ""));
ReceiverLink receiver = new ReceiverLink(session,
"my-receiver",
new global::Amqp.Framing.Source()
{
Address =
eventHubEntity + "/ConsumerGroups/$Default/Partitions/" + partition,
FilterSet = filters
}, null);
Amqp.Types.Symbol deviceIdKey = new Amqp.Types.Symbol("iothub-connection-device-id");
string deviceId = deviceName;
while (true)
{
if (timerCreated == false)
Timer();
receivedStarted = 1;
Amqp.Message m = await receiver.ReceiveAsync(10000);
if (m != null)
{
var id = m.MessageAnnotations.Map[deviceIdKey].ToString();
if (id == deviceId)
{
Data data = (Data)m.BodySection;
string msg = System.Text.Encoding.UTF8.GetString(data.Binary, 0, data.Binary.Length);
bool isValid = ValidateMessage(msg);
if (isValid)
{
receiver.Accept(m);
Counter.Text = parsedCounter;
Debug.Write("Receiving Message " + parsedCounter );
TimeText.Text = "The last activity was at " + parsedTime;
//Connection String
if (connection != null)
ConnectedTextBox.Text = "CONNECTED";
else
ConnectedTextBox.Text = "DISCONNECTED";
if (DelayTimer != null)
DelayTimer.Cancel();
}
else
{
receiver.Release(m);
}
}
}
}
}
我實際上通過使用以下方法解決了這個問題-this.NavigationCacheMode = Windows.UI.Xaml.Navigation.NavigationCacheMode.Enabled; -在MainPage的構造函數中。
每次導航到該頁面時,我都會重新初始化該頁面,我認為這導致該頁面與等待的任務失去同步。
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