Service feature table (manual cache)

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Display a feature layer from a service using the manual cache feature request mode.

Service feature table (manual cache) sample

Use case

AGSServiceFeatureTable supports three request modes, which define how features are requested from the service and stored in the local table. The feature request modes have different performance characteristics. Use manual cache in scenarios where you want to explicitly control requests for features.

How to use the sample

Run the sample and pan and zoom around the map. No features will be requested and displayed automatically. Tap the Populate button, and features will display.

How it works

  1. Set the featureRequestMode property of the AGSServiceFeatureTable to AGSFeatureRequestMode.manualCache before the table is loaded.
  2. Load the table.
  3. Use AGSServiceFeatureTable.populateFromService(with:clearCache:outFields:completion:) on the table to request features.

Relevant API

  • AGSFeatureLayer
  • AGSFeatureRequestMode
  • AGSFeatureRequestMode.manualCache
  • AGSServiceFeatureTable
  • AGSServiceFeatureTable.featureRequestMode
  • AGSServiceFeatureTable.populateFromService(with:clearCache:outFields:completion:)

About the data

This sample uses the Incidents in San Francisco feature layer. The sample opens with an initial visible extent centered over San Francisco, CA.

Additional information

In manual cache mode, features are never automatically populated from the service. All features are loaded manually using the AGSServiceFeatureTable.populateFromService method.

Tags

cache, feature request mode, performance

Sample Code

ManualCacheViewController.swift
                                                                  
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// Copyright 2016 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.

import UIKit
import ArcGIS

class ManualCacheViewController: UIViewController {
    @IBOutlet private weak var mapView: AGSMapView!

    var featureTable: AGSServiceFeatureTable!

    override func viewDidLoad() {
        super.viewDidLoad()

        // add the source code button item to the right of navigation bar
        (self.navigationItem.rightBarButtonItem as! SourceCodeBarButtonItem).filenames = ["ManualCacheViewController"]

        // initialize map with topographic basemap
        let map = AGSMap(basemapStyle: .arcGISTopographic)

        // create feature table using a url
        self.featureTable = AGSServiceFeatureTable(url: URL(string: "https://sampleserver6.arcgisonline.com/arcgis/rest/services/SF311/FeatureServer/0")!)
        // set the feature request mode to Manual Cache
        featureTable.featureRequestMode = AGSFeatureRequestMode.manualCache
        // create feature layer using this feature table
        let featureLayer = AGSFeatureLayer(featureTable: self.featureTable)
        // add feature layer to the map
        map.operationalLayers.add(featureLayer)

        // assign map to the map view
        mapView.map = map
        mapView.setViewpoint(AGSViewpoint(center: AGSPoint(x: -13630484, y: 4545415, spatialReference: .webMercator()), scale: 500000))
    }

    // MARK: - Actions

    @IBAction func populateAction(_ sender: AnyObject) {
        // set query parameters
        let params = AGSQueryParameters()
        // for specific request type
        params.whereClause = "req_Type = 'Tree Maintenance or Damage'"

        // populate features based on query
        self.featureTable.populateFromService(with: params, clearCache: true, outFields: ["*"]) { [weak self] (result: AGSFeatureQueryResult?, error: Error?) in
            // check for error
            if let error = error {
                self?.presentAlert(error: error)
            } else {
                // the resulting features should be displayed on the map
                // you can print the count of features
                print("Populated \(result?.featureEnumerator().allObjects.count ?? 0) features.")
            }
        }
    }
}

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