fix(angular): ionTabsWillChange is fired before tab activation (#27991)

Issue number: Resolves #27212

---------

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issue. -->

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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

`ionTabsWillChange` emits _after_ the tab view is activated in the
stack.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

- `ionTabsWillChange` emits _before_ the tab view is activated in the
stack.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

<!-- If this introduces a breaking change, please describe the impact
and migration path for existing applications below. -->


## Other information

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screenshots of how the component looks before and after the change. -->

Dev-build: `7.2.4-dev.11692040948.1fd0ecd2`

Author: sean-perkins

packages/angular/src/directives/navigation/ion-router-outlet.ts

@@ -30,7 +30,7 @@ import { Config } from '../../providers/config';
 import { NavController } from '../../providers/nav-controller';
 
 import { StackController } from './stack-controller';
-import { RouteView, getUrl } from './stack-utils';
+import { RouteView, StackDidChangeEvent, StackWillChangeEvent, getUrl, isTabSwitch } from './stack-utils';
 
 // TODO(FW-2827): types
 
@@ -66,7 +66,11 @@ export class IonRouterOutlet implements OnDestroy, OnInit {
    */
   @Input() name = PRIMARY_OUTLET;
 
-  @Output() stackEvents = new EventEmitter<any>();
+  /** @internal */
+  @Output() stackWillChange = new EventEmitter<StackWillChangeEvent>();
+  /** @internal */
+  @Output() stackDidChange = new EventEmitter<StackDidChangeEvent>();
+
   // eslint-disable-next-line @angular-eslint/no-output-rename
   @Output('activate') activateEvents = new EventEmitter<any>();
   // eslint-disable-next-line @angular-eslint/no-output-rename
@@ -304,9 +308,16 @@ export class IonRouterOutlet implements OnDestroy, OnInit {
      */
     this.navCtrl.setTopOutlet(this);
 
+    const leavingView = this.stackCtrl.getActiveView();
+
+    this.stackWillChange.emit({
+      enteringView,
+      tabSwitch: isTabSwitch(enteringView, leavingView),
+    });
+
     this.stackCtrl.setActive(enteringView).then((data) => {
       this.activateEvents.emit(cmpRef.instance);
-      this.stackEvents.emit(data);
+      this.stackDidChange.emit(data);
     });
   }
 

packages/angular/src/directives/navigation/ion-tabs.ts

@@ -16,14 +16,19 @@ import { NavController } from '../../providers/nav-controller';
 import { IonTabBar } from '../proxies';
 
 import { IonRouterOutlet } from './ion-router-outlet';
-import { StackEvent } from './stack-utils';
+import { StackDidChangeEvent, StackWillChangeEvent } from './stack-utils';
 
 @Component({
   selector: 'ion-tabs',
   template: `
     <ng-content select="[slot=top]"></ng-content>
     <div class="tabs-inner" #tabsInner>
-      <ion-router-outlet #outlet tabs="true" (stackEvents)="onPageSelected($event)"></ion-router-outlet>
+      <ion-router-outlet
+        #outlet
+        tabs="true"
+        (stackWillChange)="onStackWillChange($event)"
+        (stackDidChange)="onStackDidChange($event)"
+      ></ion-router-outlet>
     </div>
     <ng-content></ng-content>
   `,
@@ -62,7 +67,13 @@ export class IonTabs implements AfterContentInit, AfterContentChecked {
   @ContentChild(IonTabBar, { static: false }) tabBar: IonTabBar | undefined;
   @ContentChildren(IonTabBar) tabBars: QueryList<IonTabBar>;
 
+  /**
+   * Emitted before the tab view is changed.
+   */
   @Output() ionTabsWillChange = new EventEmitter<{ tab: string }>();
+  /**
+   * Emitted after the tab view is changed.
+   */
   @Output() ionTabsDidChange = new EventEmitter<{ tab: string }>();
 
   private tabBarSlot = 'bottom';
@@ -80,10 +91,19 @@ export class IonTabs implements AfterContentInit, AfterContentChecked {
   /**
    * @internal
    */
-  onPageSelected(detail: StackEvent): void {
-    const stackId = detail.enteringView.stackId;
-    if (detail.tabSwitch && stackId !== undefined) {
+  onStackWillChange({ enteringView, tabSwitch }: StackWillChangeEvent): void {
+    const stackId = enteringView.stackId;
+    if (tabSwitch && stackId !== undefined) {
       this.ionTabsWillChange.emit({ tab: stackId });
+    }
+  }
+
+  /**
+   * @internal
+   */
+  onStackDidChange({ enteringView, tabSwitch }: StackDidChangeEvent): void {
+    const stackId = enteringView.stackId;
+    if (tabSwitch && stackId !== undefined) {
       if (this.tabBar) {
         this.tabBar.selectedTab = stackId;
       }

packages/angular/src/directives/navigation/stack-controller.ts

@@ -8,7 +8,7 @@ import { NavController } from '../../providers/nav-controller';
 
 import {
   RouteView,
-  StackEvent,
+  StackDidChangeEvent,
   computeStackId,
   destroyView,
   getUrl,
@@ -61,7 +61,7 @@ export class StackController {
     return view;
   }
 
-  setActive(enteringView: RouteView): Promise<StackEvent> {
+  setActive(enteringView: RouteView): Promise<StackDidChangeEvent> {
     const consumeResult = this.navCtrl.consumeTransition();
     let { direction, animation, animationBuilder } = consumeResult;
     const leavingView = this.activeView;
@@ -224,6 +224,13 @@ export class StackController {
     return this.activeView ? this.activeView.stackId : undefined;
   }
 
+  /**
+   * @internal
+   */
+  getActiveView(): RouteView | undefined {
+    return this.activeView;
+  }
+
   hasRunningTask(): boolean {
     return this.runningTask !== undefined;
   }

packages/angular/src/directives/navigation/stack-utils.ts

@@ -79,10 +79,23 @@ export const destroyView = (view: RouteView | undefined): void => {
   }
 };
 
-export interface StackEvent {
+export interface StackWillChangeEvent {
+  enteringView: RouteView;
+  /**
+   * `true` if the event is trigged as a result of a switch
+   * between tab navigation stacks.
+   */
+  tabSwitch: boolean;
+}
+
+export interface StackDidChangeEvent {
   enteringView: RouteView;
   direction: RouterDirection;
   animation: NavDirection | undefined;
+  /**
+   * `true` if the event is trigged as a result of a switch
+   * between tab navigation stacks.
+   */
   tabSwitch: boolean;
 }