Added SwitchMerge

Author: sllethe

src/lib/list/selection-list.ts

@@ -32,6 +32,15 @@ import {Focusable} from '../core/a11y/focus-key-manager';
 import {MdListOption} from './list-option';
 import {CanDisable, mixinDisabled} from '../core/common-behaviors/disabled';
 import {RxChain, switchMap, first, filter} from '../core/rxjs/index';
+import 'rxjs/add/observable/merge';
+import 'rxjs/add/observable/fromEvent';
+import 'rxjs/add/operator/filter';
+import 'rxjs/add/operator/switchMap';
+import 'rxjs/add/observable/of';
+import {merge} from 'rxjs/operator/merge';
+import {Observable} from 'rxjs/Observable';
+import 'rxjs/add/operator/switchMap';
+import 'rxjs/add/operator/startWith';
 
 export class MdSelectionListBase {}
 export const _MdSelectionListMixinBase = mixinDisabled(MdSelectionListBase);
@@ -59,15 +68,15 @@ export class MdSelectionList extends _MdSelectionListMixinBase
   /** Tab index for the selection-list. */
   _tabIndex = 0;
 
-  /** Track which options we're listening to for focus/destruction. */
-  private _subscribed: WeakMap<MdListOption, boolean> = new WeakMap();
-
   /** Subscription to tabbing out from the selection-list. */
   private _tabOutSubscription: Subscription;
 
   /** Subscription to option changes from the selection-list. */
   private _optionsChangeSubscription: Subscription;
 
+  private _optionsChangeSubscriptionOnFocus: Subscription;
+  private _optionsChangeSubscriptionDestory: Subscription;
+
   /** The FocusKeyManager which handles focus. */
   _keyManager: FocusKeyManager;
 
@@ -96,13 +105,8 @@ export class MdSelectionList extends _MdSelectionListMixinBase
       this._tabIndex = -1;
     }
 
-    // Go ahead and subscribe all of the initial options
-    this._subscribeOptions(this.options);
-    // When the list changes, re-subscribe
-    this._optionsChangeSubscription =
-      this.options.changes.subscribe((options: QueryList<MdListOption>) => {
-        this._subscribeOptions(options);
-      });
+    this._optionsChangeSubscriptionOnFocus = this.onFocusSubscription();
+    this._optionsChangeSubscriptionDestory = this.onDestorySubscription();
   }
 
   ngOnDestroy(): void {
@@ -119,6 +123,32 @@ export class MdSelectionList extends _MdSelectionListMixinBase
     this._element.nativeElement.focus();
   }
 
+  onDestorySubscription(): Subscription {
+    return this.options.changes.startWith(this.options).switchMap((options) => {
+      return Observable.merge(...options.map(option => option.destroy));
+    }).subscribe(e => {
+      let optionIndex: number = this.options.toArray().indexOf(e.option);
+      if (e.option._hasFocus) {
+        // Check whether the option is the last item
+        if (optionIndex < this.options.length - 1) {
+          this._keyManager.setActiveItem(optionIndex);
+        } else if (optionIndex - 1 >= 0) {
+          this._keyManager.setActiveItem(optionIndex - 1);
+        }
+      }
+      e.option.destroy.unsubscribe();
+    });
+  }
+
+  onFocusSubscription(): Subscription {
+    return this.options.changes.startWith(this.options).switchMap((options) => {
+      return Observable.merge(...options.map(option => option.onFocus));
+    }).subscribe(e => {
+      let optionIndex: number = this.options.toArray().indexOf(e.option);
+      this._keyManager.updateActiveItemIndex(optionIndex);
+    });
+  }
+
   /** Passes relevant key presses to our key manager. */
   keydown(event: KeyboardEvent) {
     switch (event.keyCode) {
@@ -145,56 +175,6 @@ export class MdSelectionList extends _MdSelectionListMixinBase
     }
   }
 
-  /**
-   * Iterate through the list of options and add them to our list of
-   * subscribed options.
-   *
-   * @param options The list of options to be subscribed.
-   */
-  protected _subscribeOptions(options: QueryList<MdListOption>): void {
-    options.forEach(option => this._addOption(option));
-  }
-
-  /**
-   * Add a specific option to our subscribed list. If the option has
-   * already been subscribed, this ensures it is only subscribed
-   * once.
-   *
-   * @param option The option to be subscribed (or checked for existing
-   * subscription).
-   */
-  protected _addOption(option: MdListOption) {
-    // If we've already been subscribed to a parent, do nothing
-    if (this._subscribed.has(option)) {
-      return;
-    }
-
-    // Watch for focus events outside of the keyboard navigation
-    option.onFocus.subscribe(() => {
-      let optionIndex: number = this.options.toArray().indexOf(option);
-      this._keyManager.updateActiveItemIndex(optionIndex);
-    });
-
-    // On destroy, remove the item from our list, and check focus
-    option.destroy.subscribe(() => {
-      let optionIndex: number = this.options.toArray().indexOf(option);
-
-      if (option._hasFocus) {
-        // Check whether the option is the last item
-        if (optionIndex < this.options.length - 1) {
-          this._keyManager.setActiveItem(optionIndex);
-        } else if (optionIndex - 1 >= 0) {
-          this._keyManager.setActiveItem(optionIndex - 1);
-        }
-      }
-
-      this._subscribed.delete(option);
-      option.destroy.unsubscribe();
-    });
-
-    this._subscribed.set(option, true);
-  }
-
   /**
    * Utility to ensure all indexes are valid.
    *