Add custom dynamic entity data source

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Create a custom dynamic entity data source and display it using a dynamic entity layer.

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Use case

Developers can create a custom DynamicEntityDataSource to be able to visualize data from a variety of different feeds as dynamic entities using a DynamicEntityLayer. An example of this is in a mobile situational awareness app, where a custom DynamicEntityDataSource can be used to connect to peer-to-peer feeds in order to visualize real-time location tracks from teammates in the field.

How to use the sample

Run the sample to view the map and the dynamic entity layer displaying the latest observation from the custom data source. Tap on a dynamic entity to view its attributes in a callout.

How it works

Configure the custom data source:

  1. Create a custom data source implementation of a DynamicEntityDataSource.
  2. Override OnLoadAsync() to specify the DynamicEntityDataSourceInfo for a given unique entity ID field and a list of Field objects matching the fields in the data source.
  3. Override OnConnectAsync() to begin processing observations from the custom data source.
  4. Loop through the observations and deserialize each observation into a MapPoint object and a Dictionary<string, object> containing the attributes.
  5. Use DynamicEntityDataSource.AddObservation(mapPoint, attributes) to add each observation to the custom data source.

Configure the map view:

  1. Create a DynamicEntityLayer using the custom data source implementation.
  2. Update values in the layer's TrackDisplayProperties to customize the layer's appearance.
  3. Set up the layer's LabelDefinitions to display labels for each dynamic entity.
  4. Configure a GeoViewTapped event handler on the MapView to select a dynamic entity and display the entity's attributes in a callout.

Relevant API

  • DynamicEntity
  • DynamicEntityDataSource
  • DynamicEntityLayer
  • LabelDefinition
  • TrackDisplayProperties

About the data

This sample uses a .json file containing observations of marine vessels in the Pacific North West hosted on ArcGIS Online.

Additional information

In this sample, we iterate through features in a GeoJSON file to mimic messages coming from a real-time feed. You can create a custom dyamic entity data source to process any data that contains observations which can be translated into MapPoint objects with associated Dictionary<string, object> attributes.

Tags

data, dynamic, entity, label, labeling, live, real-time, stream, track

Sample Code

SimulatedDataSource.csSimulatedDataSource.csAddCustomDynamicEntityDataSource.xaml.csAddCustomDynamicEntityDataSource.xaml
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// Copyright 2023 Esri.
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
// You may obtain a copy of the License at: http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific
// language governing permissions and limitations under the License.

using Esri.ArcGISRuntime.Data;
using Esri.ArcGISRuntime.Geometry;
using Esri.ArcGISRuntime.RealTime;
using System.Diagnostics;
using System.Text.Json;


namespace ArcGIS.Samples.AddCustomDynamicEntityDataSource
{
    public class SimulatedDataSource : DynamicEntityDataSource
    {
        // Hold a reference to the file stream reader, the process task, and the cancellation token source.
        private Task? _processTask;
        private StreamReader? _streamReader;
        private CancellationTokenSource? _cancellationTokenSource;
        private List<Field> _fields;

        public SimulatedDataSource(string filePath, string entityIdField, TimeSpan delay)
        {
            FilePath = filePath;
            EntityIdField = entityIdField;
            Delay = delay;
        }

        #region Properties

        // Expose the file path, entity ID field, and delay length as properties.
        public string FilePath { get; }
        public string EntityIdField { get; }
        public TimeSpan Delay { get; }

        #endregion

        protected override async Task<DynamicEntityDataSourceInfo> OnLoadAsync()
        {
            // Derive schema from the first row in the custom data source.
            _fields = GetSchema();

            // Open the file for processing.
            Stream stream = File.OpenRead(FilePath);
            _streamReader = new StreamReader(stream);

            // Create a new DynamicEntityDataSourceInfo using the entity ID field and the fields derived from the attributes of each observation in the custom data source.
            return new DynamicEntityDataSourceInfo(EntityIdField, _fields) { SpatialReference = SpatialReferences.Wgs84 };
        }

        protected override Task OnConnectAsync(CancellationToken cancellationToken)
        {
            // On connecting to the custom data source begin processing the file.
            _cancellationTokenSource = new();
            _processTask = Task.Run(() => ObservationProcessLoopAsync(), _cancellationTokenSource.Token);
            return Task.CompletedTask;
        }

        protected override async Task OnDisconnectAsync()
        {
            // On disconnecting from the custom data source, stop processing the file.
            _cancellationTokenSource?.Cancel();

            if (_processTask is not null) await _processTask;

            _cancellationTokenSource = null;
            _processTask = null;
        }

        private async Task ObservationProcessLoopAsync()
        {
            try
            {
                while (!_cancellationTokenSource!.IsCancellationRequested)
                {
                    // Process the next observation.
                    var processed = await ProcessNextObservation();

                    // If the end of the file has been reached, break out of the loop.
                    if (_streamReader.EndOfStream) break;

                    // If the observation was not processed, continue to the next observation.
                    if (!processed) continue;

                    // If there is no delay, yield to the UI thread otherwise delay for the specified amount of time.
                    if (Delay == TimeSpan.Zero)
                    {
                        await Task.Yield();
                    }
                    else
                    {
                        await Task.Delay(Delay, _cancellationTokenSource.Token);
                    }
                }
            }
            catch (Exception ex)
            {
                Debug.WriteLine(ex.ToString());
            }
        }

        private async Task<bool> ProcessNextObservation()
        {
            _ = _streamReader ?? throw new ArgumentNullException("File stream not available.");

            // Read the next observation.
            var json = await _streamReader.ReadLineAsync();

            // If there is no json to read or the schema is not available, return false.
            if (string.IsNullOrEmpty(json) || _fields is null) return false;

            try
            {
                JsonElement jsonElement = JsonSerializer.Deserialize<JsonElement>(json);

                // Create a new MapPoint from the x and y coordinates of the observation.
                MapPoint? point = null;
                if (jsonElement.TryGetProperty("geometry", out JsonElement jsonGeometry))
                {
                    point = new MapPoint(
                        jsonGeometry.GetProperty("x").GetDouble(),
                        jsonGeometry.GetProperty("y").GetDouble(),
                        SpatialReferences.Wgs84);
                }

                // Get the dictionary of attributes from the observation using the field names as keys.
                Dictionary<string, object?> attributes = new();
                if (jsonElement.TryGetProperty("attributes", out JsonElement jsonAttributes))
                {
                    foreach (var field in _fields)
                    {
                        if (jsonAttributes.TryGetProperty(field.Name, out JsonElement prop))
                        {
                            object? value = null;
                            if (prop.ValueKind != JsonValueKind.Null)
                            {
                                if (prop.ValueKind == JsonValueKind.Number && field.FieldType == FieldType.Float64)
                                {
                                    value = prop.GetDouble();
                                }
                                else if (prop.ValueKind == JsonValueKind.Number && field.FieldType == FieldType.Int32)
                                {
                                    value = prop.GetInt32();
                                }
                                else if (prop.ValueKind == JsonValueKind.String)
                                {
                                    value = prop.GetString();
                                }
                            }
                            attributes.Add(field.Name, value);
                        }
                    }
                }

                // Add the observation to the custom data source.
                AddObservation(point, attributes);
                return true;
            }
            catch (Exception ex)
            {
                Debug.WriteLine($"{ex}");
                return false;
            }
        }

        private static List<Field> GetSchema()
        {
            // Return a list of fields matching the attributes of each observation in the custom data source.
            return new List<Field>()
            {
                new Field(FieldType.Text, "MMSI", string.Empty, 256),
                new Field(FieldType.Float64, "BaseDateTime", string.Empty, 8),
                new Field(FieldType.Float64, "LAT", string.Empty, 8),
                new Field(FieldType.Float64, "LONG", string.Empty, 8),
                new Field(FieldType.Float64, "SOG", string.Empty, 8),
                new Field(FieldType.Float64, "COG", string.Empty, 8),
                new Field(FieldType.Float64, "Heading", string.Empty, 8),
                new Field(FieldType.Text, "VesselName", string.Empty, 256),
                new Field(FieldType.Text, "IMO", string.Empty, 256),
                new Field(FieldType.Text, "CallSign", string.Empty, 256),
                new Field(FieldType.Text, "VesselType", string.Empty, 256),
                new Field(FieldType.Text, "Status", string.Empty, 256),
                new Field(FieldType.Float64, "Length", string.Empty, 8),
                new Field(FieldType.Float64, "Width", string.Empty, 8),
                new Field(FieldType.Text, "Cargo", string.Empty, 256),
                new Field(FieldType.Text, "globalid", string.Empty, 256)
            };
        }
    }
}

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