topic Re: Feature layer dynamic query features display in ArcGIS API for Silverlight Questions

Feature layer dynamic query features display

HugoCardenas — Mon, 03 Oct 2011 15:05:13 GMT

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.

Re: Feature layer dynamic query features display

JenniferNery — Mon, 03 Oct 2011 19:49:08 GMT

How about updating the FeatureLayer.Where clause to include previous clause?
WHERE = "AlertType = 14 or AlertType = 11"

Calling FeatureLayer.Update() will query the service and return features that match the above condition.

Re: Feature layer dynamic query features display

HugoCardenas — Sat, 11 Dec 2021 09:14:48 GMT

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.