fix(nav): reset zIndex when goes under 0

Closes #5718

ionic/components/nav/nav-controller.ts

@@ -1261,8 +1261,18 @@ export class NavController extends Ion {
       view.destroy();
     });
 
+    // if any z-index goes under 0, then reset them all
+    let shouldResetZIndex = this._views.some(v => v.zIndex < 0);
+    if (shouldResetZIndex) {
+      this._views.forEach(view => {
+        view.setZIndex( view.zIndex + INIT_ZINDEX + 1, this._renderer );
+      });
+    }
   }
 
+  /**
+   * @private
+   */
   ngOnDestroy() {
     for (var i = this._views.length - 1; i >= 0; i--) {
       this._views[i].destroy();

ionic/components/nav/test/nav-controller.spec.ts

@@ -350,6 +350,30 @@ export function run() {
         expect(view2.destroy).toHaveBeenCalled();
         expect(view3.destroy).toHaveBeenCalled();
       });
+
+      it('should reset zIndexes if their is a negative zindex', () => {
+        let view1 = new ViewController(Page1);
+        view1.setPageRef( getElementRef() );
+        view1.state = STATE_INACTIVE;
+        view1.zIndex = -1;
+
+        let view2 = new ViewController(Page2);
+        view2.setPageRef( getElementRef() );
+        view2.state = STATE_INACTIVE;
+        view2.zIndex = 0;
+
+        let view3 = new ViewController(Page3);
+        view3.setPageRef( getElementRef() );
+        view3.state = STATE_ACTIVE;
+        view3.zIndex = 1;
+
+        nav._views = [view1, view2, view3];
+        nav._cleanup();
+
+        expect(view1.zIndex).toEqual(10);
+        expect(view2.zIndex).toEqual(11);
+        expect(view3.zIndex).toEqual(12);
+      });
     });
 
     describe('_postRender', () => {
@@ -747,7 +771,7 @@ export function run() {
 
         nav._transFinish(1, enteringView, leavingView, 'back', hasCompleted);
 
-        expect(nav._cleanup).toHaveBeenCalled()
+        expect(nav._cleanup).toHaveBeenCalled();
       });
 
       it('should not run cleanup when most not recent transition', () => {
@@ -763,7 +787,7 @@ export function run() {
 
         nav._transFinish(2, enteringView, leavingView, 'back', hasCompleted);
 
-        expect(nav._cleanup).not.toHaveBeenCalled()
+        expect(nav._cleanup).not.toHaveBeenCalled();
       });
 
       it('should not run cleanup when it hasnt completed transition, but is the most recent', () => {
@@ -779,7 +803,7 @@ export function run() {
 
         nav._transFinish(1, enteringView, leavingView, 'back', hasCompleted);
 
-        expect(nav._cleanup).not.toHaveBeenCalled()
+        expect(nav._cleanup).not.toHaveBeenCalled();
       });
 
       it('should set transitioning is over when most recent transition finishes', () => {
@@ -1150,9 +1174,7 @@ export function run() {
     });
 
     function mockNav() {
-      let elementRef = {
-        nativeElement: document.createElement('div')
-      };
+      let elementRef = getElementRef();
 
       let nav = new NavController(null, null, config, null, elementRef, null, null, null, null, null);
 
@@ -1178,6 +1200,12 @@ export function run() {
       return nav;
     }
 
+    function getElementRef() {
+      return {
+        nativeElement: document.createElement('div')
+      }
+    }
+
   });
 }