make autosize work along rows

Author: Ales Rechtorik

src/demo-app/input/input-demo.html

@@ -78,14 +78,25 @@ <h4>Textarea</h4>
 <md-card class="demo-card demo-basic">
   <md-toolbar color="primary">Expanding textarea</md-toolbar>
   <md-card-content>
-    <p>
+    <div>
       <md-textarea
         placeholder="Textarea with autosize"
         class="demo-full-width"
         autosize
         value="Hello world. How are you?">
       </md-textarea>
-    </p>
+    </div>
+
+    <h4>With `rows` explicitly set</h4>
+    <div>
+      <md-textarea
+        placeholder="Textarea with autosize"
+        class="demo-full-width"
+        autosize
+        rows="8"
+        value="Hello world. How are you?">
+      </md-textarea>
+    </div>
   </md-card-content>
 </md-card>
 

src/lib/input/input.ts

@@ -5,6 +5,7 @@ import {
   Input,
   Directive,
   AfterContentInit,
+  Attribute,
   OnInit,
   ContentChild,
   HostListener,
@@ -101,32 +102,116 @@ export class MdHint {
   selector: 'textarea[mdAutosize]'
 })
 export class MdAutosize implements OnInit {
+  // public because of AOT
   @HostListener('input')
-  private _onChange() {
+  public _onChange() {
     if (this._isActive) {
       this._adjust();
     }
   }
 
+  // public because of AOT
   @Input('mdAutosize')
-  private _isActive: boolean;
+  public _isActive: boolean;
+
+  // public because of AOT
+  // TODO: change to a setter, to recalculate on change
+  @Input('attr.rows')
+  public _rows: string;
+
+  private _height: number;
+  private _lineHeight: number;
 
   constructor(private _elRef: ElementRef) {}
 
   ngOnInit() {
     if (this._isActive) {
       this._elRef.nativeElement.style.overflow = 'hidden';
+
+      // check is rows is explicitly set, otherwise we don't need to
+      // care about it(and getting the actual line-height) at all
+      if (this._rows) {
+        this._lineHeight = this._getLineHeight();
+        this._elRef.nativeElement.style.minHeight = `${+this._rows * this._lineHeight}px`;
+      }
+
       this._adjust();
     }
   }
 
   private _adjust() {
+    // reset height(and rows if it was set by the user)
+    // to the default values to properly calculate new height
     this._elRef.nativeElement.style.height = 'auto';
-    this._elRef.nativeElement.style.height = `${this._elRef.nativeElement.scrollHeight}px`;
+
+    // only need to do this if user explicitly set rows
+    if (this._rows) {
+      this._elRef.nativeElement.rows = this._rows;
+    }
+
+    this._height = +this._elRef.nativeElement.scrollHeight;
+
+    // only need to do this if user explicitly set rows
+    if (this._rows) {
+      this._elRef.nativeElement.rows = this._getCalculatedRows();
+    }
+
+    this._elRef.nativeElement.style.height = `${this._height}px`;
+  }
+
+  private _getCalculatedRows() {
+    return Math.round(this._height / this._lineHeight);
+  }
+
+  private _getLineHeight(): number {
+    const el: HTMLElement = this._elRef.nativeElement;
+
+    // get the actual computed styles for the element
+    const computedStyles = window.getComputedStyle(el);
+
+    // if line height is explicitly set(to a pixel value), use that
+    if (computedStyles.lineHeight && computedStyles.lineHeight.toLowerCase().indexOf('px') >= 0) {
+      // return stripped of the "px" and as a number
+      return +computedStyles.lineHeight.replace('px', '');
+    }
+
+    // create temporary element
+    const tempEl = document.createElement(el.nodeName);
+
+    // reset styling, visually hiden the element
+    // and set its font styles to match the ones of our textarea
+    tempEl.setAttribute('rows', '1');
+    tempEl.setAttribute(
+      'style',
+      `
+        margin: 0px;
+        padding: 0px;
+        visibility: hidden;
+        opacity: 0;
+        font-family: ${computedStyles.fontFamily};
+        font-size: ${computedStyles.fontSize};
+      `
+    );
+
+    // fill in one row
+    tempEl.innerHTML = '-';
+
+    // append to parent element to correctly inherit same values
+    // as the actual textarea
+    el.parentNode.appendChild(tempEl);
+
+    // get the actual line height
+    const lineHeight = tempEl.clientHeight;
+
+    // cleanup
+    tempEl.parentNode.removeChild(tempEl);
+
+    return lineHeight;
   }
 }
 
 
+
 /**
  * Component that represents a text input. It encapsulates the <input> HTMLElement and
  * improve on its behaviour, along with styling it according to the Material Design.