订阅和搜索

搜索和订阅流数据

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await QueuedTask.Run(async () =>
{
  //query filter can be null to search and retrieve all rows
  //true means recycling cursor
  using (var rc = streamLayer.SearchAndSubscribe(qfilter, true))
  {
    //waiting for new features to be streamed
    //default is no cancellation
    while (await rc.WaitForRowsAsync())
    {
      while (rc.MoveNext())
      {
        using (var row = rc.Current)
        {
          //determine the origin of the row event
          switch (row.GetRowSource())
          {
            case RealtimeRowSource.PreExisting:
              //pre-existing row at the time of subscribe
              continue;
            case RealtimeRowSource.EventInsert:
              //row was inserted after subscribe
              continue;
            case RealtimeRowSource.EventDelete:
              //row was deleted after subscribe
              continue;
          }
        }
      }
    }
  }//row cursor is disposed. row cursor is unsubscribed

  //....or....
  //Use the feature class instead of the layer
  using (var rfc = streamLayer.GetFeatureClass())
  {
    //non-recycling cursor - 2nd param "false"
    using (var rc = rfc.SearchAndSubscribe(qfilter, false))
    {
      //waiting for new features to be streamed
      //default is no cancellation
      while (await rc.WaitForRowsAsync())
      {
        //etc
      }
    }
  }
});

搜索和订阅取消

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await QueuedTask.Run(async () =>
{
  //Recycling cursor - 2nd param "true"
  //or streamLayer.Subscribe(qfilter, true) to just subscribe
  using (var rc = streamLayer.SearchAndSubscribe(qfilter, true))
  {
    //auto-cancel after 20 seconds
    var cancel = new CancellationTokenSource(new TimeSpan(0, 0, 20));
    //catch TaskCanceledException
    try
    {
      while (await rc.WaitForRowsAsync(cancel.Token))
      {
        //check for row events
        while (rc.MoveNext())
        {
          using (var row = rc.Current)
          {
            //etc
          }
        }
      }
    }
    catch (TaskCanceledException tce)
    {
      //Handle cancellation as needed
    }
    cancel.Dispose();
  }
});

显式取消等待行异步

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//somewhere in our code we create a CancellationTokenSource
var cancel = new CancellationTokenSource();
//...

//call cancel on the CancellationTokenSource anywhere in
//the add-in, assuming the CancellationTokenSource is in scope
if (SomeConditionForCancel)
  cancel.Cancel();//<-- will cancel the token

//Within QueuedTask we are subscribed! streamLayer.Subscribe() or SearchAndSubscribe()
try
{
  //TaskCanceledException will be thrown when the token is cancelled
  while (await rc.WaitForRowsAsync(cancel.Token))
  {
    //check for row events
    while (rc.MoveNext())
    {
      using (var row = rc.Current)
      {
        //etc
      }
    }
  }
}
catch (TaskCanceledException tce)
{
  //Handle cancellation as needed
}
cancel.Dispose();

;