How do you loop through every Checkbox in Div? (dart)

Issue

I have a div in my html:

<div id="list_container_id"></div>

To which I add Checkbox(es) through dart

CheckboxInputElement cie = new CheckboxInputElement();
LabelElement label = new LabelElement();
    cie.id="checkboxid_"+asdf;//unique id
    label.htmlFor = 'checkboxid_'+asdf;//bind Label to checkbox
    label.text = asdf;
    list_container.children.add(cie);
    list_container.children.add(label);
    list_container.children.add(new Element.html("<br>"));//linebreak after the checkbox

later, I want to get a list of all values of the Checkboxes that are checked on Button click. The following code happens onClick:

List list = [];    
for (CheckboxInputElement elem in list_container.children){
        if(elem.checked){
          list.add(elem.value);
        }
      }

As far as I understand it, that for loop goes trough every Checkbox that is in the list_container, but for some reason, it throws an Error when it reaches a label:

Breaking on exception: type ‘LabelElement’ is not a subtype of type
‘CheckboxInputElement’ of ‘elem’.

I don’t understand why the for loop even bothers with the Labels when I stated clearly that elem should be a CheckboxInputElement. How would be the right way to do this?

Solution

You don’t state that it only should return CheckboxInputElement you state that the variable holding the values processed in the loop should only hold CheckboxInputElements but the loop assigns every element it encounters.

This way you get only CheckboxInputElement

List list = [];    
for (var elem in list_container.children.where((e) => e is CheckboxInputElement)){
  if(elem.checked){
    list.add(elem.value);
  }
}

or

list.addAll(list_container.children
  .where((e) => e is CheckboxInputElement && e.checked)
  .map((e) => e.value));

or

list.addAll(querySelectorAll('#list_container_id input[type="checkbox"]')
  .where((e) => e is CheckboxInputElement && e.checked)
  .map((e) => e.value));

Answered By – Günter Zöchbauer

Answer Checked By – Katrina (FlutterFixes Volunteer)