refactor: more efficient sorting of the selected options

Author: crisbeto

src/lib/core/selection/selection.spec.ts

@@ -156,6 +156,26 @@ describe('SelectionModel', () => {
     });
   });
 
+  describe('disabling the change event', () => {
+    let model: SelectionModel<any>;
+
+    beforeEach(() => {
+      model = new SelectionModel(true, null, false);
+    });
+
+    it('should not have an onChange stream if change events are disabled', () => {
+      expect(model.onChange).toBeFalsy();
+    });
+
+    it('should still update the select value', () => {
+      model.select(1);
+      expect(model.selected).toEqual([1]);
+
+      model.select(2);
+      expect(model.selected).toEqual([1, 2]);
+    });
+  });
+
   it('should be able to determine whether it is empty', () => {
     let model = new SelectionModel();
 

src/lib/core/selection/selection.ts

@@ -28,9 +28,13 @@ export class SelectionModel<T> {
   }
 
   /** Event emitted when the value has changed. */
-  onChange: Subject<SelectionChange<T>> = new Subject();
+  onChange: Subject<SelectionChange<T>> = this._emitChanges ? new Subject() : null;
+
+  constructor(
+    private _isMulti = false,
+    initiallySelectedValues?: T[],
+    private _emitChanges = true) {
 
-  constructor(private _isMulti = false, initiallySelectedValues?: T[]) {
     if (initiallySelectedValues) {
       if (_isMulti) {
         initiallySelectedValues.forEach(value => this._markSelected(value));
@@ -112,8 +116,9 @@ export class SelectionModel<T> {
       this.onChange.next(eventData);
       this._deselectedToEmit = [];
       this._selectedToEmit = [];
-      this._selected = null;
     }
+
+    this._selected = null;
   }
 
   /** Selects a value. */
@@ -124,17 +129,23 @@ export class SelectionModel<T> {
       }
 
       this._selection.add(value);
-      this._selectedToEmit.push(value);
+
+      if (this._emitChanges) {
+        this._selectedToEmit.push(value);
+      }
     }
   }
 
-   /** Deselects a value. */
-   private _unmarkSelected(value: T) {
-     if (this.isSelected(value)) {
-       this._selection.delete(value);
-       this._deselectedToEmit.push(value);
-     }
-   }
+  /** Deselects a value. */
+  private _unmarkSelected(value: T) {
+    if (this.isSelected(value)) {
+      this._selection.delete(value);
+
+      if (this._emitChanges) {
+        this._deselectedToEmit.push(value);
+      }
+    }
+  }
 
   /** Clears out the selected values. */
   private _unmarkAll() {

src/lib/select/select.ts

@@ -289,7 +289,7 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
   }
 
   ngAfterContentInit() {
-    this._selectionModel = new SelectionModel<MdOption>(this.multiple);
+    this._selectionModel = new SelectionModel<MdOption>(this.multiple, null, false);
     this._initKeyManager();
 
     this._changeSubscription = this.options.changes.startWith(null).subscribe(() => {
@@ -562,13 +562,13 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
 
     if (this.multiple) {
       this._selectionModel.toggle(option);
+      wasSelected ? option.deselect() : option.select();
+      this._sortValues();
     } else {
       this._clearSelection(option);
       this._selectionModel.select(option);
     }
 
-    this._sortValues();
-
     if (wasSelected !== this._selectionModel.isSelected(option)) {
       this._propagateChanges();
     }
@@ -580,8 +580,13 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
    */
   private _sortValues(): void {
     if (this._multiple) {
-      const options = this.options.toArray();
-      this._selectionModel.sort((a, b) => options.indexOf(a) - options.indexOf(b));
+      this._selectionModel.clear();
+
+      this.options.forEach(option => {
+        if (option.selected) {
+          this._selectionModel.select(option);
+        }
+      });
     }
   }