Create Dropdown menu with Angular Signal with default value and an extra option

i have an array that is a computed signal, this is the definition:

selectableBoxeOptions(): Signal<BoxOptions[]|null>

these are all the boxeOptions you can select in a dropdown menu.

i have another computed signal and its call selectedBox. this is its definition:

selectedBox: Signal<Box | undefined>

BoxOptions object is not the same as the Box object.

selectedBox signal gets its value from the boxService.

i want to create a dropdown menu that the options are boxOptions in boxService.selectableBoxeOptions(). the display text for each option would be boxOption.model.name.

it should also have an option called "None", when its none, it means the selectedBox is undefined or null.

when the dropdown loads, it should have one of the options selected already.

the selected option depends on whats selectedBox.

if selectedBox() is undefined or null, the selected option would be "None".

if selectedBox() is not undefined or null, one of the other options should be selected. this is how the selectedBox() is mapped to the boxOption in boxService.selectableBoxeOptions(): boxOption.device.serial === selectedBox()?.device.serial.

the user can choose a different option with the dropdown.

when the user selects the "None" option, it should call a method called boxService.deselectBox() which will make the selectedBox() undefined.

when the user selects other options, it should call a method called boxService.selectBox, and it would pass in the box.device.serial like this boxService.selectBox(box.device.serial) which would set the selectedBox with a box.

the code i have is not working, please help. this is angular 18:

<b-drop-down

label="Select A Box">

<select

[value]="selectedBox()?.device"

aria-describedby="boxes">

<option [selected]="selectedBox() == null" value="None">None</option>

@for (boxOptionof mService.selectableBoxes(); track boxOption.device.serial) {

<option [selected]="boxOption.device.serial === selectedBox()?.device.serial" [value]="box.device.serial">

{{ boxOption.model.name }}

</option>

}

</select>

</b-drop-down>

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