Leaflet Proxy: The "Clear Shapes" Mystery
Problem: When using Leaflet Proxy, the clearShapes function works perfectly the first time it's called, but subsequent calls fail to remove data (dots) that have been added to the map.
Scenario: You're building a Leaflet application where you want to dynamically add and remove points on a map. You're using Leaflet Proxy to manage the data and display it on the map. The initial removal of data works, but subsequent calls to clearShapes seem to be ignored.
Example Code:
// Initialize Leaflet Proxy
var myProxy = L.esri.leafletProxy();
// Add points to the map
function addPointsToMap(data) {
data.forEach(point => {
var marker = L.marker([point.lat, point.lng]).addTo(map);
myProxy.addShape(marker);
});
}
// Clear the points on the map
function clearPoints() {
myProxy.clearShapes();
}
// Triggering the functions
addPointsToMap([
{ lat: 40.7128, lng: -74.0060 },
{ lat: 34.0522, lng: -118.2437 }
]);
clearPoints(); // Works!
addPointsToMap([
{ lat: 37.7749, lng: -122.4194 },
{ lat: 41.8781, lng: -87.6298 }
]);
clearPoints(); // Doesn't clear the map!
Analysis:
The root cause of this issue lies in how Leaflet Proxy handles the clearShapes function. When you call clearShapes for the first time, it effectively clears the entire layer used by Leaflet Proxy to display the data. However, this clearing action is not persistent.
Subsequently, when you add new data to the map, Leaflet Proxy uses the same underlying layer, effectively overlaying the new data on top of the previously cleared one.
Solution:
To consistently clear the map using clearShapes, you need to refresh the Leaflet Proxy layer after each clearing action. You can do this by using the createProxy function, which effectively initializes a new layer.
Modified Code:
// Initialize Leaflet Proxy
var myProxy = L.esri.leafletProxy();
// Add points to the map
function addPointsToMap(data) {
data.forEach(point => {
var marker = L.marker([point.lat, point.lng]).addTo(map);
myProxy.addShape(marker);
});
}
// Clear the points on the map
function clearPoints() {
myProxy.clearShapes();
myProxy = L.esri.leafletProxy(); // Refresh Leaflet Proxy
}
// Triggering the functions
addPointsToMap([
{ lat: 40.7128, lng: -74.0060 },
{ lat: 34.0522, lng: -118.2437 }
]);
clearPoints(); // Works!
addPointsToMap([
{ lat: 37.7749, lng: -122.4194 },
{ lat: 41.8781, lng: -87.6298 }
]);
clearPoints(); // Now works too!
Additional Value:
Remember that the clearShapes method doesn't necessarily remove the data from your application's memory. It only removes the visual representation of the data from the map.
If you want to completely clear the data from your application, you'll need to ensure the data array holding the points is also cleared or reinitialized.
References:
By understanding this behavior and implementing the solution outlined above, you can effectively use clearShapes in your Leaflet Proxy applications, ensuring consistent clearing of data on the map.
