dialogRef.afterClosed().subscribe(result => {
      console.log("result", result);
      this.onModalClosePassData.emit(result);//emit to parent
    });

parent component.html

<ng-template #showTextOnly>
        <child-component [branch]="releaseBranch" [date]="dateString"
                  (onModalClosePassData)="updateComment($event)">
        </child-component>
</ng-template>

parent component.ts

//This method is getting called when i click on backDrop,

child-component.html

<button class="btn btn-default" (click)="openDialog()">Login</button>

child-component.ts

export class ChildComponent implements OnInit {
    @Output() onModalClosePassData = new EventEmitter();
    constructor(public dialog: MatDialog) { }
    openDialog(): void {
    const dialogConfig = new MatDialogConfig();
    dialogConfig.disableClose = false;
    dialogConfig.autoFocus = false;
    dialogConfig.hasBackdrop= true;
    dialogConfig.width = '300px';
    dialogConfig.autoFocus=true;
    dialogConfig.data = {branch: this.branch, date: this.date};
    const dialogRef = this.dialog.open(LoginDialog, dialogConfig);

    dialogRef.afterClosed().subscribe(result => {
      console.log("result", result); //result is getting called in both cases
      this.onModalClosePassData.emit();
    });
 }
}

LoginDialog.component.ts

import {MatDialogRef, MAT_DIALOG_DATA} from '@angular/material/dialog';
export class LoginDialog implements OnInit{
    constructor(private loginService: LoginService, public dialogRef: MatDialogRef<LoginDialog>,
      @Inject(MAT_DIALOG_DATA) public data: any) {}
      public submitForm = (formValue: any) => {
      if (this.noteForm.valid) {
        let encryptData = btoa(`${formValue.username}:${formValue.password}`);
        this.loginService.login(encryptData)
         .subscribe((response:any)=>{
             if(response.STATUS === "FAILED"){
             } else {
              this.dialogRef.close(this.noteDetail);
             }
        })
      }
    }

}
LoginDialog.component.html

<form [formGroup]="noteForm" autocomplete="off" novalidate (ngSubmit)="submitForm(noteForm.value)">
<mat-dialog-content class="mat-typography">
        <mat-form-field>
                <mat-label>User Name</mat-label>
                <input matInput type="text" formControlName="username" id="username">
        </mat-form-field>
        <mat-form-field>
                <mat-label>Password</mat-label>
                <input matInput type="password" formControlName="password">
        </mat-form-field>
</mat-dialog-content>
<mat-dialog-actions align="center">
  <button mat-raised-button color="primary" [disabled]="!noteForm.valid">Submit</button>
</mat-dialog-actions>
</form>