(onSelectChange) output for mdOption ALWAYS gets passed first item in list

问题

I'm using Angular Material for Angular 4 (4.3.4) and I need to hook into the selection event to clear the input and store the object in a separate list. But there's a problem: the onSelectChange output ALWAYS gets the first item as the parameter! What's going on?

Here's my template:

<md-autocomplete [displayWith]="displayRole" #auto="mdAutocomplete">
    <md-option 
        *ngFor="let role of roles | acrole: roleField.value | slice:0:4; let i=index;" 
        [value]="role"
        (onSelectionChange)="AddRole(role)" >
        <div class="label">
          {{role.label}}
        </div>
    </md-option>                    
</md-autocomplete>

And here's my AddRole function:

AddRole(role: Role)
{  
   // role is always the first role in the list, no matter which option I clicked on.
   this.selectedList.push(role) 
}

回答1:

With onSelectionChange event, it is possible to differentiate when the item is selected or unselected. You need to pass an $event to the target method in order to differentiate between the two cases.

Here are the changes you need to make in order to make your changes work:

In your component html:

<md-autocomplete [displayWith]="displayRole" #auto="mdAutocomplete">
    <md-option 
        *ngFor="let role of roles | acrole: roleField.value | slice:0:4; let i=index;" 
        [value]="role" 
        (onSelectionChange)="AddRole($event, role)">

        <div class="label">
            {{role.label}}
        </div>
    </md-option>
</md-autocomplete>

... and in your component.ts, change the method to following:

AddRole(event: MdOptionSelectionChange, role: Role) {  
    if (event.source.selected) {
        this.selectedList.push(role);
    }
}

---

Here is a PLUNKER DEMO based on the Material documentation example. The documentation needs to be a bit more clear about these changes.

来源：https://stackoverflow.com/questions/45664699/onselectchange-output-for-mdoption-always-gets-passed-first-item-in-list