select list set selected item angular 2 ngModel

问题:

This is my current code:

<select name="role" [(ngModel)]="user.role">
    <option *ngFor="let role of roles" [ngValue]="role" [attr.selected]="role == user.role ? 'true' : 'false'">{{role.name}}</option>
</select>

I'm loading all the roles in an array, and the user class has a Role attribute (which is not loaded like user.role = roles[0] but just through the backend data).

The problem is that the selected attribute is not working, and my select is not going to the correct role. What am I doing wrong?

回答1:

Just remove

[attr.selected]="role == user.role ? 'true' : 'false'"

and assign the selected role to user.role and ngModel will make the matching item the selected one.

If the role is an object, the assigned instance needs to be identical.

See also the recently added custom comparison https://github.com/angular/angular/issues/13268 available since 4.0.0-beta.7

<select [compareWith]="compareFn" ...

compareFn(val1, val2): boolean {
  return val1 && val2 ? val1.id === val2.id : val1 === val2;
}

回答2:

You don't need to use [attr.selected]. [(ngModel)]="user.role" is two-way data-binding, it will select the matched option from your list if value is equal to user.role. And you can also use basic [value]

<select name="role" [(ngModel)]="user.role">
    <option *ngFor="let role of roles" [value]="role">{{role.name}}</option>
</select>

回答3:

<select [ngModel]="selectedDevice" (ngModelChange)="onChange($event)" name="sel2">
    <option [value]="i" *ngFor="let i of devices">{{i}}</option>
</select>

onChange(newValue) {
    console.log(newValue);
    this.selectedDevice = newValue;\
}