fix(core): Deregister directive on destroy

fixes #53

Author: Airblader

projects/ngqp/core/src/lib/directives/query-param-group.service.ts

@@ -108,6 +108,18 @@ export class QueryParamGroupService implements OnDestroy {
         this.directives.push(directive);
     }
 
+    /**
+     * Deregisters a {@link QueryParamNameDirective} directive.
+     */
+    public removeQueryParam(directive: QueryParamNameDirective): void {
+        const index = this.directives.indexOf(directive);
+        if (index === -1) {
+            return;
+        }
+
+        this.directives.splice(index, 1);
+    }
+
     private startSynchronization() {
         this.setupGroupChangeListener();
         this.setupParamChangeListeners();

projects/ngqp/core/src/lib/directives/query-param-name.directive.ts

@@ -1,4 +1,4 @@
-import { Directive, Inject, Input, OnChanges, Optional, Self, SimpleChanges } from '@angular/core';
+import { Directive, Inject, Input, OnChanges, OnDestroy, Optional, Self, SimpleChanges } from '@angular/core';
 import { ControlValueAccessor, NG_VALUE_ACCESSOR } from '@angular/forms';
 import { DefaultControlValueAccessorDirective, NGQP_BUILT_IN_ACCESSORS } from '../accessors/accessors';
 import { QueryParamGroupService } from './query-param-group.service';
@@ -13,7 +13,7 @@ import { QueryParamGroupService } from './query-param-group.service';
 @Directive({
     selector: '[queryParamName]',
 })
-export class QueryParamNameDirective implements OnChanges {
+export class QueryParamNameDirective implements OnChanges, OnDestroy {
 
     /**
      * The name of the {@link QueryParam} inside its parent {@link QueryParamGroup}.
@@ -53,6 +53,13 @@ export class QueryParamNameDirective implements OnChanges {
         }
     }
 
+    /** @ignore */
+    public ngOnDestroy() {
+        if (this.groupService) {
+            this.groupService.removeQueryParam(this);
+        }
+    }
+
     /**
      * This resembles the selectControlValueAccessor function from
      *   https://github.com/angular/angular/blob/7.1.2/packages/forms/src/directives/shared.ts#L186