使用覆蓋警告檢查內容標籤

Question

void device_DeviceArrived(ProximityDevice sender) 
    { 
     //Compatible Device enters area 
     if (stance == WriteStage.PREP) 
     { 
      System.Diagnostics.Debug.WriteLine("Writestages won"); 
      //Perhaps here 
      updateStatusRectangle(Colors.Yellow); 
      stance = WriteStage.WRITING; 
      updateStatusText("Writing..."); 
      writeToTag(msg); 
     } 
     else 
     { 
      updateReceivedText("Device connected!"); 
     } 
    } 

private void MessageReceivedHandler(ProximityDevice sender, ProximityMessage message) 
    { 
     System.Diagnostics.Debug.WriteLine("Handler ran"); 
     var rawMsg = message.Data.ToArray(); 
     var ndefMessage = NdefMessage.FromByteArray(rawMsg); 
     foreach (NdefRecord record in ndefMessage) 
     { 
      System.Diagnostics.Debug.WriteLine("Record type: " + Encoding.UTF8.GetString(record.Type, 0, record.Type.Length)); 
      var specType = record.CheckSpecializedType(false); 
      if (specType == typeof(NdefTextRecord)) 
      { 
       var textrec = new NdefTextRecord(record); 
       updateReceivedText(textrec.Text); 
      } 

     } 
    } 

上述事件和處理程序在手機與NFC設備接觸時執行。對於這個應用程序的意圖和目的，我需要確保在寫入卡之前，如果它已經有內容，它會提示用戶驗證覆蓋數據。我評論了我認爲應該去的地方，但就檢查消息而言，我不知道如何去做。我不能在沒有ProximityMessage的情況下調用處理程序，並且我不知道另一種查看消息的方式。

問題：是否可以從device_DeviceArrived調用MessageReceivedHandler（或者檢查消息）？ （注意：Debug.Writelines是爲了測試目的，而這只是一個快速的NFC編寫器，我正在扔在一起）。

更新：在試圖找到解決辦法時，我遇到了一個不同的問題。

public bool promptUserForOverwrite() 
    { 
     bool response = false; 
     Dispatcher.BeginInvoke(() => 
      { 
       MessageBoxResult cc = MessageBox.Show("You are about to overwrite data. Proceed?", "Overwrite?", MessageBoxButton.OKCancel); 
       if (cc == MessageBoxResult.OK) 
       { 
        System.Diagnostics.Debug.WriteLine("MessageBox OK result"); 
        response = true; 
       } 
      }); 
     return response; 
    } 

private void MessageReceivedHandler(ProximityDevice sender, ProximityMessage message) 
    { 

     System.Diagnostics.Debug.WriteLine("Handler ran"); 
     var rawMsg = message.Data.ToArray(); 
     var ndefMessage = NdefMessage.FromByteArray(rawMsg); 
     foreach (NdefRecord record in ndefMessage) 
     { 
      System.Diagnostics.Debug.WriteLine("Record type: " + Encoding.UTF8.GetString(record.Type, 0, record.Type.Length)); 
      var specType = record.CheckSpecializedType(false); 
      if (specType == typeof(NdefTextRecord)) 
      { 
       var textrec = new NdefTextRecord(record); 
       updateReceivedText(textrec.Text); 
      } 
     } 
     bool pow = promptUserForOverwrite(); 

     if (!pow) 
     { 
      System.Diagnostics.Debug.WriteLine("Prompt returned"); 
      //This always hits - pow is always false. 
     } 

     if (stance == WriteStage.WRITING && pow) 
     { 
      //writeToTag(msg); 
     } 
    } 

這將作爲一種工作;問題是beginInvoke方法。我需要它來交叉線程訪問，但像這樣使用它似乎使它在稍後運行（當線程是免費的？）。 bool pow始終是錯誤的，即使我在messagebox上單擊確定（已調試，並且確實得到結果，但在我不能再使用它之後）。有沒有其他的方法可以用於Dispatcher？

Answer 1

醜，但我有這個工作。你需要得到從UI線程的TaskScheduler，所以聲明

private TaskScheduler sched; 

再上裝載的事件的頁面

sched = TaskScheduler.FromCurrentSynchronizationContext(); 

然後你的方法

public async Task<bool> promptUserForOverwrite() 
{  
    return false; 
} 

private async void MessageReceivedHandler(ProximityDevice sender, ProximityMessage message) 
{ 

    System.Diagnostics.Debug.WriteLine("Handler ran"); 
    var rawMsg = message.Data.ToArray(); 
    var ndefMessage = NdefMessage.FromByteArray(rawMsg); 
    foreach (NdefRecord record in ndefMessage) 
    { 
     System.Diagnostics.Debug.WriteLine("Record type: " + Encoding.UTF8.GetString(record.Type, 0, record.Type.Length)); 
     var specType = record.CheckSpecializedType(false); 
     if (specType == typeof(NdefTextRecord)) 
     { 
      var textrec = new NdefTextRecord(record); 
      updateReceivedText(textrec.Text); 
     } 
    } 


    var task = promptUserForOverwrite(); 

    var pow = await task.ContinueWith(t => 
    { 
      MessageBoxResult cc = MessageBox.Show("You are about to overwrite data. Proceed?", "Overwrite?", MessageBoxButton.OKCancel); 
      if (cc == MessageBoxResult.OK) 
      { 
       System.Diagnostics.Debug.WriteLine("MessageBox OK result"); 
       return true; 
      } 
      else 
      { 
       return false; 
      } 
    }, CancellationToken.None, TaskContinuationOptions.OnlyOnFaulted, sched); 

    if (!pow) 
    { 
     System.Diagnostics.Debug.WriteLine("Prompt returned"); 
     //This always hits - pow is always false. 
    } 

    if (stance == WriteStage.WRITING && pow) 
    { 
     //writeToTag(msg); 
    } 
}