Select All mat option and deselect All

Question

I have scenario as below:

I want to achieve is:

1. When user click on All then all options shall be selected and when user click All again then all options shall be deselcted.
2. If All option is checked and user click any other checkbox than All then All and clicked checkbox shall be deselected.
3. When user selects 4 options one by one then All shall be selected.

HTML file

<mat-select placeholder="User Type" formControlName="UserType" multiple>
    <mat-option *ngFor="let filters of userTypeFilters" [value]="filters.key">
          {{filters.value}}
    </mat-option>
        <mat-option #allSelected (click)="toggleAllSelection()" [value]="0">All</mat-option>
</mat-select>

TS file

this.searchUserForm = this.fb.group({
  userType: new FormControl('')
});

userTypeFilters = [
  {
    key: 1, value: 'Value 1',
  },
  {
    key: 2, value: 'Value 2',
  },
  {
    key: 3, value: 'Value 3',
  },
  {
    key: 4, value: 'Value 4',
  }
]

toggleAllSelection() {
  if (this.allSelected.selected) {
    this.searchUserForm.controls.userType
    .patchValue([...this.userTypeFilters.map(item => item.key), 0]);
  } else {
    this.searchUserForm.controls.userType.patchValue([]);
  }
}

Now, how to achieve 2nd and 3rd point

Stackblitz is: https://stackblitz.com/edit/angular-material-with-angular-v5-znfehg?file=app/app.component.html

Answer 1

Use code as below create function on click each mat-option and select()/deselect() all option:

See stackblitz:https://stackblitz.com/edit/angular-material-with-angular-v5-jsgvx6?file=app/app.component.html

TS:

tosslePerOne(all){ 
   if (this.allSelected.selected) {  
    this.allSelected.deselect();
    return false;
}
  if(this.searchUserForm.controls.userType.value.length==this.userTypeFilters.length)
    this.allSelected.select();

}
  toggleAllSelection() {
    if (this.allSelected.selected) {
      this.searchUserForm.controls.userType
        .patchValue([...this.userTypeFilters.map(item => item.key), 0]);
    } else {
      this.searchUserForm.controls.userType.patchValue([]);
    }
  }

HTML:

<form [formGroup]="searchUserForm" fxFlex fxLayout="column" autocomplete="off" style="margin: 30px">
    <mat-select placeholder="User Type" formControlName="userType" multiple>
        <mat-option *ngFor="let filters of userTypeFilters" [value]="filters.key" (click)="tosslePerOne(allSelected.viewValue)">
            {{filters.value}}
        </mat-option>
        <mat-option #allSelected (click)="toggleAllSelection()" [value]="0">All</mat-option>
    </mat-select>
</form>

Answer 2

Another way to do this is with the @ViewChild selector to get the mat-select component and troggle the mat-options items selected or unselected. We need also a variable to save the selected actual status to select or unselect all the elements on every click. Hope will help.

  import {MatOption, MatSelect} from "@angular/material";
  
  export class ExampleAllSelector {
  
    myFormControl = new FormControl();
    elements: any[] = [];

    allSelected = false;

    @ViewChild('mySel') skillSel: MatSelect;

    constructor() {}

    toggleAllSelection() {
      this.allSelected = !this.allSelected;  // to control select-unselect
      
      if (this.skillAllSelected) {
        this.skillSel.options.forEach( (item : MatOption) => item.select());
      } else {
        this.skillSel.options.forEach( (item : MatOption) => {item.deselect()});
      }
      this.skillSel.close();
    }
  }

      <mat-select #mySel placeholder="Example" [formControl]="myFormControl" multiple>
        <mat-option [value]="0" (click)="toggleAllSelection()">All items</mat-option>
        <mat-option *ngFor="let element of elements" [value]="element">{{skill.name}}</mat-option>
      </mat-select>