Trigger event on re-selecting same value on mat-se

问题:

I'm working on a mat-table which implements pagination, filtering, selection, etc. I have this mat-select on one of the header columns which I use to set a global value for all the other mat-select on the same column... Like this

Everything works good so far, but lets say I choose a global value, and then I increase the pageSize of the table, the rows that already had the selection will stay that way, but the new additional rows will have the default value; now if I go to the global mat-select again and click on the same option to apply the value to the new rows, nothing will occur since I'm not actually changing the selection; so I'm trying to basically fire the SelectionChange event of the mat-select again even though the value is actually the same.

Any help is greatly appreciated, I'm thinking there must be a really simple way to make this work but I'm not seeing it; if any additional info is needed let me know!

回答1:

I know this is late, but I've come to find a solution.

Normally, we would be using @Output() selectionChange to pass the selected value to a function in our .ts file and do what we want there. But this doesn't work if we select the same value.

Solution:

So what we need to do instead is use @Output() openedChange which will pass true (opened) or false (closed). We are interested in when we close the mat-select component. Unfortunately openedChange doesn't have direct access to the value we selected. So we simply make a member variable which is binded to the value we select, and whenever openedChange is triggered and returns false, we will use that member variable.

Here's the basic code:

your-component.component.html

<mat-form-field>
  <mat-label>Options</mat-label>
  <mat-select *ngFor="let option of allOptions;"
              (openedChange)="onSelectionChange($event)"
              [(value)]="selectedVariable">
    <mat-option [value]="option">
      {{option.name}}
    </mat-option>
  </mat-select>
</mat-form-field>

your-component.component.ts

  selectedVariable: any;

  constructor() {}

  ngOnInit() {
    //...
  }

  onSelectionChange(opened: boolean) {
    if (!opened && this.selectedVariable) {
      // Do whatever you want here with `this.selectedVariable`
      console.log(this.selectedVariable);
    }
  }

Note: In the onSelectionChange function, you need to make sure that something was actually selected. Because otherwise the function will continue if a user clicks on the select, and clicks away from it without selecting anything.

回答2:

This is a little bit of a "workaround", but I wonder if you could leverage:

@Output() openedChange: EventEmitter

Event emitted when the select panel has been toggled.

And fire your function any time the select is changed or closed, as I believe that is essentially what you're looking to accomplish.

However, you might have to add some logic to prevent your function from being fired twice.