How can I check if a mat-menu in Material Angular is open?

I faced the same suituation. And I made a CSS work around.

While we click on the menu a custom aria tag is appended to the menu and get removed while we close the dropdoen. With this we can use CSS custom selector (It works with most mordern browsers)

.parentclass a[aria-expanded] { whatever you need }

Some case (if button)

.parentclass button[aria-expanded] { whatever you need }

Thanks,

You can bind your method on "menuOpened", that method will be invoked whenever Menu is opened

<mat-menu #menu="matMenu" [overlapTrigger]="false" (menuOpened)="isOpened($event)" panelClass="custom">
                    <a routerLink="/attendence/detail" mat-menu-item>View Attendance</a>
                    <a routerLink="/adherence/detail" mat-menu-item>View Adherece</a>
                    <button mat-menu-item>Edit Agent</button>
                    <button mat-menu-item>Upload photo</button>
                    <button mat-menu-item>Deactivate Agent</button>
                </mat-menu>

And add this method in your component,

isOpened(evt:any){
// set you flag here that you can use in ng-class for the button.
}

Hope this helps.

You can use Material matMenuTrigger directive to check whether the menu is open or not

<button mat-button [matMenuTriggerFor]="menu"   #t="matMenuTrigger">Menu</button>
<mat-menu #menu="matMenu">
  <button mat-menu-item>Item 1</button>
  <button mat-menu-item>Item 2</button>
</mat-menu>
{{t.menuOpen}}

Check the example here: https://stackblitz.com/edit/angular-9hbzdw

Now you use ngClass binding to change the style of your button!

 <button mat-stroked-button mdbWavesEffect [matMenuTriggerFor]="menu">Actions</button>
            <mat-menu #menu="matMenu" [overlapTrigger]="false" panelClass="custom">
                <a routerLink="/attendence/detail" mat-menu-item>View Attendance</a>
                <a routerLink="/adherence/detail" mat-menu-item>View Adherece</a>
                <button [ngClass]="selectedMenuItem ===1 ? 'active' : ''" (click)="onSelectMenuItem(1)" mat-menu-item>Edit Agent</button>
                <button [ngClass]="selectedMenuItem ===2 ? 'active' : ''" (click)="onSelectMenuItem(2)" mat-menu-item>Upload photo</button>
                <button [ngClass]="selectedMenuItem ===3 ? 'active' : ''" (click)="onSelectMenuItem(3)" mat-menu-item>Deactivate Agent</button>
            </mat-menu>

selectedMenuItem = 1 // Initial value set to 1 onSelectMenuItem(id): void { this.selectedMenuItem = id; }