fix(viewcontroller): onDidDismiss() is always called

fixes ionic-team#8223

src/components/app/app.ts

@@ -79,7 +79,10 @@ export class App {
       // During developement, navPop can be triggered by calling
       // window.ClickBackButton();
       if (!window['HWBackButton']) {
-        window['HWBackButton'] = this.goBack.bind(this);
+        window['HWBackButton'] = () => {
+          let p = this.goBack();
+          p && p.catch(() => console.debug('hardware go back cancelled'));
+        };
       }
     });
   }
@@ -239,7 +242,7 @@ export class App {
       return this._menuCtrl.close();
     }
 
-    let navPromise = this.navPop();
+    const navPromise = this.navPop();
     if (navPromise === null) {
       // no views to go back to
       // let's exit the app

src/components/tabs/tabs.ts

@@ -383,7 +383,7 @@ export class Tabs extends Ion implements AfterViewInit {
     let deselectedPage: ViewController;
     if (deselectedTab) {
       deselectedPage = deselectedTab.getActive();
-      deselectedPage && deselectedPage._willLeave();
+      deselectedPage && deselectedPage._willLeave(false);
     }
 
     opts.animate = false;

src/navigation/nav-controller-base.ts

@@ -270,7 +270,10 @@ export class NavControllerBase extends Ion implements NavController {
     const leavingView = this.getActive();
     const enteringView = this._getEnteringView(ti, leavingView);
 
-    assert(leavingView || enteringView, 'both leavingView and enteringView are null');
+    if (!leavingView && !enteringView) {
+      ti.reject('leavingView and enteringView are null. stack is already empty');
+      return false;
+    }
 
     // set that this nav is actively transitioning
     this.setTransitioning(true);
@@ -423,7 +426,7 @@ export class NavControllerBase extends Ion implements NavController {
       this._zone.run(() => {
         for (i = 0; i < destroyQueue.length; i++) {
           view = destroyQueue[i];
-          this._willLeave(view);
+          this._willLeave(view, true);
           this._didLeave(view);
           this._willUnload(view);
         }
@@ -682,7 +685,7 @@ export class NavControllerBase extends Ion implements NavController {
     if (enteringView || leavingView) {
       this._zone.run(() => {
         // Here, the order is important. WillLeave must called before WillEnter.
-        leavingView && this._willLeave(leavingView);
+        leavingView && this._willLeave(leavingView, !enteringView);
         enteringView && this._willEnter(enteringView);
       });
     }
@@ -856,11 +859,11 @@ export class NavControllerBase extends Ion implements NavController {
     this._app.viewDidEnter.emit(view);
   }
 
-  _willLeave(view: ViewController) {
+  _willLeave(view: ViewController, willUnload: boolean) {
     assert(this.isTransitioning(), 'nav controller should be transitioning');
     assert(NgZone.isInAngularZone(), 'callback should be zoned');
 
-    view._willLeave();
+    view._willLeave(willUnload);
     this.viewWillLeave.emit(view);
     this._app.viewWillLeave.emit(view);
   }

src/navigation/test/view-controller.spec.ts

@@ -50,7 +50,7 @@ describe('ViewController', () => {
       });
 
       // act
-      viewController._willLeave();
+      viewController._willLeave(false);
     }, 10000);
   });
 

src/navigation/view-controller.ts

@@ -38,6 +38,8 @@ export class ViewController {
   private _nb: Navbar;
   private _onDidDismiss: Function;
   private _onWillDismiss: Function;
+  private _dismissData: any;
+  private _dismissRole: any;
   private _detached: boolean;
 
   /**
@@ -164,20 +166,16 @@ export class ViewController {
    * @param {any} [role ]
    * @param {NavOptions} NavOptions Options for the dismiss navigation.
    * @returns {any} data Returns the data passed in, if any.
-   *
    */
   dismiss(data?: any, role?: any, navOptions: NavOptions = {}): Promise<any> {
     if (!this._nav) {
       return Promise.resolve(false);
     }
+    this._dismissData = data;
+    this._dismissRole = role;
 
     let options = assign({}, this._leavingOpts, navOptions);
-    this._onWillDismiss && this._onWillDismiss(data, role);
-    return this._nav.removeView(this, options).then(() => {
-      this._onDidDismiss && this._onDidDismiss(data, role);
-      this._onDidDismiss = null;
-      return data;
-    });
+    return this._nav.removeView(this, options).then(() => data);
   }
 
   /**
@@ -489,9 +487,13 @@ export class ViewController {
    * @private
    * The view has is about to leave and no longer be the active view.
    */
-  _willLeave() {
+  _willLeave(willUnload: boolean) {
     this.willLeave.emit(null);
     this._lifecycle('WillLeave');
+
+    if (willUnload && this._onWillDismiss) {
+      this._onWillDismiss(this._dismissData, this._dismissRole);
+    }
   }
 
   /**
@@ -517,6 +519,9 @@ export class ViewController {
   _willUnload() {
     this.willUnload.emit(null);
     this._lifecycle('WillUnload');
+
+    this._onDidDismiss && this._onDidDismiss(this._dismissData, this._dismissRole);
+    this._onDidDismiss = null;
   }
 
   /**