Feature layer dynamic query features display

HugoCardenas

Is there a way to display new sets of features on the map without deleting existing or currently diplayed ones?

Initially, when the page loads for the first time, I display on screen a set of features (cf. XAML code below):

<esri:FeatureLayer ID="MyMeters" Renderer="{StaticResource AlertTypesRenderer}" Where="AlertType = 14" ... />

At run time, the user has a set of check boxes to display any other alerts and remove from the screen the previously loaded ones (cf. C# code bewlow):

ESRI.ArcGIS.Client.FeatureLayer fs = new ESRI.ArcGIS.Client.FeatureLayer();
fs.Where = "AlertType = 11";

At this point, the user has checked-off the "14" and checked the "11" alerts.  If I call a "ClearGraphics" method on the feature layer right before displaying the new features, "ClearGraphics" actually deletes the previous features permanently from the feature service!  Hence, I create a new instance of the "FeatureLayer" (cf. C# code above), rather than referencing the existing instance like this:

FeatureLayer fs = MyMap.Layers["MyMeters"] as FeatureLayer;

I have tried other options like:

1.  Removing the entire MyMap.Layers["MyMeters"] and inserting a new one (in the same index position as that of the previous one) with the new features.

2. Creating a new graphics layers and add this one to the MyMap.Layers collection.

These two options work fine, BUT my feature data grid gets all crazy: in option 1 the feature data grid references the feature layer that is removed.  When I bind the new layer at run-time to it, it does not sync that well. In option 2, the feature data grid does not respond at all.


Perhaps I am managing the features of a feature layer the wrong way.  I think there may be a way to just "hide" or remove previous features from screen, so I can only see on screen the new ones.  In doing, so I can choose to display only the features I specify, without having to "delete" them form the Service, or without having to "remove/insert" feature layers.

Do you know any better way?  Please share it with me.

Hugo.

HugoCardenas

Thanks Jennifer!
You did it!  It was the "FeatureLayer.Update()" line that did it.
In my query, I leave out types = 14 in order to show on screen only types = 11.  The type 14 is on screen already; then, I issue a run-time query from code-behind and retrieve types = 11.  The whole idea is to remove the 14s from the screen and place the 11s instead.  It works!

I did have to add the "FeatureLayer_UpdateFailed" event in order for the "FeatureLayer_UpdateCompleted" event to execute; the latter was not executing without the former.  I use the "FeatureLayer_UpdateCompleted" event for further processing of those newly retrieved features.

The whole process is like this:

1.  Retrieve types 14 at page first load (XAML):

<esri:FeatureLayer ID="MyMeters" Renderer="{StaticResource AlertTypesRenderer}" OutFields="*" Where="AlertType = 14" Url="my-url" MouseLeftButtonDown="FeatureLayer_MouseLeftButtonDown" />

2. Bind the feature data grid to the feature layer (XAML):

<esri:FeatureDataGrid  x:Name="MyDataGrid" Map="{Binding ElementName=MyMap}"
GraphicsLayer="{Binding ElementName=MyMap, Path=Layers.[MyMeters]}" SelectionChanged="MyDataGrid_SelectionChanged" />

3. At run-time, perform another query to retrieve types = 11 and remove from screen the 14s that were retrieved at page load with XAML code (cf. step 1):

public void ReLoadMeters()
{
   // Create an instance referencing the already existing feature layer
   FeatureLayer fs = MyMap.Layers["MyMeters"] as FeatureLayer;
   
   // Set event handler on feature layer feature retrieval.
   fs.UpdateCompleted += FeatureLayer_UpdateCompleted;
   fs.UpdateFailed += new EventHandler<Tasks.TaskFailedEventArgs>(FeatureLayer_UpdateFailed);
   fs.Where = "AlertTypes = 11";
   fs.Update();
}

4.  Define the "FeatureLayer_UpdateCompleted" event for further processing of newly retrieved features:

private void FeatureLayer_UpdateCompleted(object sender, EventArgs args)
{
   FeatureLayer fs = sender as FeatureLayer;
   foreach (Graphic graphic in fs.Graphics)
  {
     // Here I do my further processing with the newly retrieved features
  }
}

5.  Define the "FeatureLayer_UpdateFailed" event handler (the event at step 4 was not firing without this one):

private void FeatureLayer_UpdateFailed(object sender, EventArgs args)
{
   FeatureLayer fs = sender as FeatureLayer;
   // Catch any errors here...
}

Now, my feature data grid and the features on screen are in syn all the time: the attributes for those features on screen are listed on the feature data grid; when I click on a map feature or on a row, the map zooms in to the feature and the row highlights.

Thanks again, Jennifer!
Hugo.