feat(slides): add method to get previous index

Slides added method wrapper: `getPreviousIndex()`

references #5508

ionic/components/slides/slides.ts

@@ -827,6 +827,15 @@ export class Slides extends Ion {
     return this.slider.activeIndex;
   }
 
+  /**
+   * Get the index of the previous slide.
+   *
+   * @returns {number} The index number of the previous slide.
+   */
+  getPreviousIndex(): number {
+    return this.slider.previousIndex;
+  }
+
   /**
    * Get the total number of slides.
    *

ionic/components/slides/swiper-widget.d.ts

@@ -3,6 +3,7 @@ export declare class Swiper {
   constructor(container: HTMLElement, params: any);
   slides: Array<HTMLElement>;
   activeIndex: number;
+  previousIndex: number;
   isEnd: boolean;
   isBeginning: boolean;
   update(): any;

ionic/components/slides/test/controller/index.ts

@@ -9,16 +9,17 @@ class MyPage {
   @ViewChild('mySlider') slider: Slides;
   mySlideOptions = {
     initialSlide: 1,
-    loop: true
+    loop: false
   };
 
   ngAfterViewInit() {
 
   }
 
   onSlideChanged() {
+    let previousIndex = this.slider.getPreviousIndex();
     let currentIndex = this.slider.getActiveIndex();
-    console.log("Current index is", currentIndex);
+    console.log("Previous index is", previousIndex, "Current index is", currentIndex);
   }
 
   goToPrevSlide() {
@@ -30,7 +31,7 @@ class MyPage {
   }
 
   goToSlide(index) {
-    this.slider.slideTo(index, 500, false);
+    this.slider.slideTo(index);
   }
 
   getIndex() {

ionic/components/slides/test/controller/main.html

@@ -1,16 +1,23 @@
 <ion-slides #mySlider [options]="mySlideOptions" (didChange)="onSlideChanged()">
   <ion-slide padding>
     <h1>Slide 1</h1>
+    <button block (click)="goToPrevSlide()">Navigate Back</button>
+    <button block (click)="goToNextSlide()">Navigate Forward</button>
     <button block (click)="goToSlide(2)">Navigate to 3rd Slide</button>
     <button block (click)="getLength()">Get Slide Length</button>
+    <button block (click)="getIndex()">Get Index</button>
   </ion-slide>
   <ion-slide padding>
     <h1>Slide 2</h1>
     <button block (click)="goToPrevSlide()">Navigate Back</button>
     <button block (click)="goToNextSlide()">Navigate Forward</button>
+    <button block (click)="goToSlide(2)">Navigate to 3rd Slide</button>
+    <button block (click)="getIndex()">Get Index</button>
   </ion-slide>
   <ion-slide padding>
     <h1>Slide 3</h1>
+    <button block (click)="goToPrevSlide()">Navigate Back</button>
+    <button block (click)="goToNextSlide()">Navigate Forward</button>
     <button block (click)="getIndex()">Get Index</button>
   </ion-slide>
 </ion-slides>