feat(select): add floatingPlaceholder option

src/demo-app/select/select-demo.html

@@ -18,7 +18,7 @@
 
   <md-card>
     <md-select placeholder="Drink" [(ngModel)]="currentDrink" [required]="isRequired" [disabled]="isDisabled"
-      #drinkControl="ngModel">
+      [floatPlaceholder]="floatPlaceholder" #drinkControl="ngModel">
       <md-option *ngFor="let drink of drinks" [value]="drink.value" [disabled]="drink.disabled">
         {{ drink.viewValue }}
       </md-option>
@@ -27,6 +27,15 @@
     <p> Touched: {{ drinkControl.touched }} </p>
     <p> Dirty: {{ drinkControl.dirty }} </p>
     <p> Status: {{ drinkControl.control?.status }} </p>
+    <p>
+      <label for="floating-placeholder">Floating placeholder:</label>
+      <select [(ngModel)]="floatPlaceholder" id="floating-placeholder">
+        <option value="auto">Auto</option>
+        <option value="always">Always</option>
+        <option value="never">Never</option>
+      </select>
+    </p>
+
     <button md-button (click)="currentDrink='water-2'">SET VALUE</button>
     <button md-button (click)="isRequired=!isRequired">TOGGLE REQUIRED</button>
     <button md-button (click)="isDisabled=!isDisabled">TOGGLE DISABLED</button>

src/demo-app/select/select-demo.ts

@@ -14,6 +14,7 @@ export class SelectDemo {
   showSelect = false;
   currentDrink: string;
   latestChangeEvent: MdSelectChange;
+  floatPlaceholder: string = 'auto';
   foodControl = new FormControl('pizza-1');
 
   foods = [

src/lib/select/select.html

@@ -1,9 +1,14 @@
 <div class="mat-select-trigger" cdk-overlay-origin (click)="toggle()" #origin="cdkOverlayOrigin" #trigger>
-  <span class="mat-select-placeholder" [class.mat-floating-placeholder]="this.selected"
-   [@transformPlaceholder]="_placeholderState" [style.width.px]="_selectedValueWidth"> {{ placeholder }} </span>
+  <span
+    class="mat-select-placeholder"
+    [class.mat-floating-placeholder]="selected"
+    [@transformPlaceholder]="_getPlaceholderAnimationState()"
+    [style.visibility]="_getPlaceholderVisibility()"
+    [style.width.px]="_selectedValueWidth"> {{ placeholder }} </span>
   <span class="mat-select-value" *ngIf="selected">
     <span class="mat-select-value-text">{{ selected?.viewValue }}</span>
   </span>
+
   <span class="mat-select-arrow"></span>
   <span class="mat-select-underline"></span>
 </div>

src/lib/select/select.spec.ts

@@ -11,7 +11,7 @@ import {
 } from '@angular/core';
 import {MdSelectModule} from './index';
 import {OverlayContainer} from '../core/overlay/overlay-container';
-import {MdSelect} from './select';
+import {MdSelect, MdSelectFloatPlaceholderType} from './select';
 import {MdOption} from '../core/option/option';
 import {Dir} from '../core/rtl/dir';
 import {
@@ -35,6 +35,7 @@ describe('MdSelect', () => {
         SelectWithChangeEvent,
         CustomSelectAccessor,
         CompWithCustomSelect,
+        FloatPlaceholderSelect,
         SelectWithErrorSibling,
         ThrowsErrorOnInit,
         BasicSelectOnPush
@@ -590,20 +591,20 @@ describe('MdSelect', () => {
     });
 
       it('should float the placeholder when the panel is open and unselected', () => {
-        expect(fixture.componentInstance.select._placeholderState)
+        expect(fixture.componentInstance.select._getPlaceholderAnimationState())
             .toEqual('', 'Expected placeholder to initially have a normal position.');
 
         trigger.click();
         fixture.detectChanges();
-        expect(fixture.componentInstance.select._placeholderState)
+        expect(fixture.componentInstance.select._getPlaceholderAnimationState())
             .toEqual('floating-ltr', 'Expected placeholder to animate up to floating position.');
 
         const backdrop =
           overlayContainerElement.querySelector('.cdk-overlay-backdrop') as HTMLElement;
         backdrop.click();
         fixture.detectChanges();
 
-        expect(fixture.componentInstance.select._placeholderState)
+        expect(fixture.componentInstance.select._getPlaceholderAnimationState())
             .toEqual('', 'Expected placeholder to animate back down to normal position.');
       });
 
@@ -616,7 +617,7 @@ describe('MdSelect', () => {
 
         expect(placeholderEl.classList)
             .toContain('mat-floating-placeholder', 'Expected placeholder to display as floating.');
-        expect(fixture.componentInstance.select._placeholderState)
+        expect(fixture.componentInstance.select._getPlaceholderAnimationState())
             .toEqual('', 'Expected animation state to be empty to avoid animation.');
       });
 
@@ -625,7 +626,8 @@ describe('MdSelect', () => {
 
         trigger.click();
         fixture.detectChanges();
-        expect(fixture.componentInstance.select._placeholderState).toEqual('floating-rtl');
+        expect(fixture.componentInstance.select._getPlaceholderAnimationState())
+            .toEqual('floating-rtl');
       });
 
 
@@ -1285,6 +1287,39 @@ describe('MdSelect', () => {
     });
   });
 
+  describe('floatPlaceholder option', () => {
+    let fixture: ComponentFixture<FloatPlaceholderSelect>;
+
+    beforeEach(() => {
+      fixture = TestBed.createComponent(FloatPlaceholderSelect);
+    });
+
+    it('should be able to disable the floating placeholder', () => {
+      let placeholder = fixture.debugElement.query(By.css('.mat-select-placeholder')).nativeElement;
+
+      fixture.componentInstance.floatPlaceholder = 'never';
+      fixture.detectChanges();
+
+      expect(placeholder.style.visibility).toBe('visible');
+      expect(fixture.componentInstance.select._getPlaceholderAnimationState()).toBeFalsy();
+
+      fixture.componentInstance.control.setValue('pizza-1');
+      fixture.detectChanges();
+
+      expect(placeholder.style.visibility).toBe('hidden');
+      expect(fixture.componentInstance.select._getPlaceholderAnimationState()).toBeFalsy();
+    });
+
+    it('should be able to always float the placeholder', () => {
+      expect(fixture.componentInstance.control.value).toBeFalsy();
+
+      fixture.componentInstance.floatPlaceholder = 'always';
+      fixture.detectChanges();
+
+      expect(fixture.componentInstance.select._getPlaceholderAnimationState()).toBe('floating-ltr');
+    });
+  });
+
   describe('with OnPush change detection', () => {
     let fixture: ComponentFixture<BasicSelectOnPush>;
     let trigger: HTMLElement;
@@ -1309,6 +1344,7 @@ describe('MdSelect', () => {
   });
 });
 
+
 @Component({
   selector: 'basic-select',
   template: `
@@ -1529,6 +1565,29 @@ class BasicSelectOnPush {
   @ViewChildren(MdOption) options: QueryList<MdOption>;
 }
 
+@Component({
+  selector: 'floating-placeholder-select',
+  template: `
+    <md-select placeholder="Food I want to eat right now" [formControl]="control"
+      [floatPlaceholder]="floatPlaceholder">
+        <md-option *ngFor="let food of foods" [value]="food.value">
+          {{ food.viewValue }}
+        </md-option>
+      </md-select>
+    `,
+})
+class FloatPlaceholderSelect {
+  floatPlaceholder: MdSelectFloatPlaceholderType = 'auto';
+  control = new FormControl();
+  foods: any[] = [
+    { value: 'steak-0', viewValue: 'Steak' },
+    { value: 'pizza-1', viewValue: 'Pizza' },
+    { value: 'tacos-2', viewValue: 'Tacos'}
+  ];
+
+  @ViewChild(MdSelect) select: MdSelect;
+}
+
 
 /**
  * TODO: Move this to core testing utility until Angular has event faking

src/lib/select/select.ts

@@ -73,6 +73,9 @@ export class MdSelectChange {
   constructor(public source: MdSelect, public value: any) { }
 }
 
+/** Allowed values for the floatPlaceholder option. */
+export type MdSelectFloatPlaceholderType = 'always' | 'never' | 'auto';
+
 @Component({
   moduleId: module.id,
   selector: 'md-select, mat-select',
@@ -128,7 +131,7 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
   private _placeholder: string;
 
   /** The animation state of the placeholder. */
-  _placeholderState = '';
+  private _placeholderState = '';
 
   /**
    * The width of the trigger. Must be saved to set the min width of the overlay panel
@@ -226,6 +229,14 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
   get required() { return this._required; }
   set required(value: any) { this._required = coerceBooleanProperty(value); }
 
+  /** Whether to float the placeholder text. */
+  @Input()
+  get floatPlaceholder(): MdSelectFloatPlaceholderType { return this._floatPlaceholder; }
+  set floatPlaceholder(value: MdSelectFloatPlaceholderType) {
+    this._floatPlaceholder = value || 'auto';
+  }
+  private _floatPlaceholder: MdSelectFloatPlaceholderType = 'auto';
+
   /** Event emitted when the select has been opened. */
   @Output() onOpen: EventEmitter<void> = new EventEmitter<void>();
 
@@ -280,7 +291,7 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
       return;
     }
     this._calculateOverlayPosition();
-    this._placeholderState = this._isRtl() ? 'floating-rtl' : 'floating-ltr';
+    this._placeholderState = this._floatPlaceholderState();
     this._panelOpen = true;
   }
 
@@ -588,6 +599,28 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
     return clampValue(0, optimalScrollPosition, maxScroll);
   }
 
+  /**
+   * Figures out the appropriate animation state for the placeholder.
+   */
+  _getPlaceholderAnimationState(): string {
+    if (this.floatPlaceholder === 'never') {
+      return '';
+    }
+
+    if (this.floatPlaceholder === 'always') {
+      return this._floatPlaceholderState();
+    }
+
+    return this._placeholderState;
+  }
+
+  /**
+   * Determines the CSS `visibility` of the placeholder element.
+   */
+  _getPlaceholderVisibility(): 'visible'|'hidden' {
+    return (this.floatPlaceholder !== 'never' || !this.selected) ? 'visible' : 'hidden';
+  }
+
   /**
    * Calculates the y-offset of the select's overlay panel in relation to the
    * top start corner of the trigger. It has to be adjusted in order for the
@@ -699,6 +732,10 @@ export class MdSelect implements AfterContentInit, ControlValueAccessor, OnDestr
     return `50% ${originY}px 0px`;
   }
 
+  /** Figures out the floating placeholder state value. */
+  private _floatPlaceholderState(): string {
+    return this._isRtl() ? 'floating-rtl' : 'floating-ltr';
+  }
 }
 
 /** Clamps a value n between min and max values. */