Selected option not selected in ngFor loop

[biologeek]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ x ] Bug report  
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior

When you create a select with ngFor, [selected] tag with an expression does not default select the correct option (and selects nothing at all) :
<select [(ngModel)]="keyboard" name="foo" class="custom-select"> <option *ngFor="let a of foo" [selected]="a.id == 1" [ngValue]="a">{{a.name}}</option> </select>

private foo: any[] = [{id: 1, name: "AZERTY"}, {id: 2, name: "QWERTY"}];

Even when keyboard model is not null, option is not selected

Expected behavior

In above case, select should show "AZERTY".
I also tested with 'keyboard' variable initialized with {id: 1, name: "AZERTY"} but value is not selected.
Tested also with string, object and number comparison expression but it does not work either.

Minimal reproduction of the problem with instructions

see code above

What is the motivation / use case for changing the behavior?

Environment

Angular version: 5.0.0

Browser:
- [ x ] Chrome (desktop) version 64.0.3282.140
- [ ] Chrome (Android) version XX
- [ ] Chrome (iOS) version XX
- [ x ] Firefox version 52.6
- [ ] Safari (desktop) version XX
- [ ] Safari (iOS) version XX
- [ ] IE version XX
- [ ] Edge version XX
 
For Tooling issues:
- Node version: 8.9.4
- Platform:  Debian

[wartab]

This absolutely not a bug. You are mixing two things that cannot work together, as they conflict.

You can solve your issue by initializing the keyboard variable:
this.keyboard = this.foo.find(keyboard => keyboard.id === 1);

[biologeek]

@wartab How would this solve my issue ? Correct me if I'm wrong but [selected] attribute should contain an expression that returns true or false. Right ?

I made some other tests following your answer that made me doubt about some funcitionalities :

HTML :

<form style="margin : 20%;">
	<div class="row">
		<div class="form-group">
			<label for="foo">K1 :{{keyboard | json}}</label>
			<select [(ngModel)]="keyboard" name="foo" class="custom-select"> 
				<option *ngFor="let a of foo" [ngValue]="a">{{a.name}}</option> 
			</select>
		</div>
	</div>
	<div class="row">


		<div class="form-group">
			<label for="fooz">K2 :{{keyboard2 | json}}</label>
			<select [(ngModel)]="keyboard2" name="fooz" class="custom-select"> 
				<option [ngValue]="foo[0]">AZERTY</option> 
				<option [ngValue]="foo[1]">QWERTY</option> 
			</select>
		</div>
	</div>
	<div class="row">


		<div class="form-group">
			<label for="fooa">K2 :{{keyboardStr | json}}</label>
			<select [(ngModel)]="keyboardStr" name="fooa" class="custom-select"> 
				<option [selected]="keyboardStr == 'AZERTY'" [ngValue]="AZERTY">AZERTY</option> 
				<option [selected]="keyboardStr == 'QWERTY'" [ngValue]="QWERTY">QWERTY</option> 
			</select>
		</div>
	</div>
	<div class="row">

		<div class="form-group">
			<label for="fooa">K2-bis :{{keyboardStr | json}}</label>
			<select [(ngModel)]="keyboardStr" name="fooa" class="custom-select"> 
				<option [selected]="keyboardStr == 'AZERTY'" [value]="AZERTY">AZERTY</option> 
				<option [selected]="keyboardStr == 'QWERTY'" [value]="QWERTY">QWERTY</option> 
			</select>
		</div>
	</div>
	<div class="row">

		<div class="form-group">
			<label for="fooa">K2-ter :{{keyboardStr | json}}</label>
			<select [(ngModel)]="keyboardStr" name="fooa" class="custom-select"> 
				<option [selected]="keyboardStr == 'AZERTY'" value="AZERTY">AZERTY</option> 
				<option [selected]="keyboardStr == 'QWERTY'" value="QWERTY">QWERTY</option> 
			</select>
		</div>
	</div>
</form>	

Component :

import { Component, OnInit } from '@angular/core';

@Component({
  selector: 'app-test',
  templateUrl: './test.component.html',
  styleUrls: ['./test.component.css']
})
export class TestComponent implements OnInit {

	private foo: any[] = [{id: 1, name: "AZERTY"}, {id: 2, name: "QWERTY"}];
	private keyboard: any = {id: 1, name: 'AZERTY'};
	private keyboard2 : any = {id: 1, name: 'AZERTY'};
	private keyboardStr : string = 'AZERTY';

  constructor() { }

  ngOnInit() {
  }

}

I am surprised that AZERTY is never default selected unless in last example:

[wartab]

You should not mix apples and oranges. Why would you use [selected] along with two way databinding? The place for your question is probably Stack Overflow, by the way.

[biologeek]

Indeed I didn't know that SelectControlValueAccessor could do the job. Issue can be closed

[jiangshanwe]

try this: SelectControlValueAccessor

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