Indeterminate State

In addition to checked and unchecked basic states, the Telerik CheckBox has a third state - Indeterminate. This means that its state is something in between - neither checked, nor unchecked. The main use case is when the checkbox owns a number of sub-options and they have different states, than the main checkbox is in indeterminate state.

To put the checkbox in the indeterminate state, set its Indeterminate parameter to true. You can bind it to a bool and bool? types, and it also exposes the IndeterminateChanged event and two-way binding.

The Indeterminate parameter maps to the indeterminate attribute of the standard HTML <input type="checkbox" />.

The Indeterminate state is something that the application logic should set to show information to the user. A user interaction with the component will clear that state and will set a true or false value to it and the Indeterminate parameter will be set to false..

For example, if you bind the checkbox to a nullable field and its value is null, you may want to show the checkbox as indeterminate.

Basic setup - show Indeterminate checkbox when its Value is not defined (null)

@* 
    This example shows how to make a checkbox indeterminate when its Value is unknown (e.g., null)
    It also shows that when the user changes the state of the CheckBox, the Indeterminate status is set to false
*@

Indeterminate: @( !TheValue.HasValue )
<br />

Checked: @TheValue
<br />

<TelerikButton Primary="true" OnClick="@( _ => TheValue = null )">Make indeterminate</TelerikButton>
<br />

<TelerikCheckBox Id="DemoCheckbox" @bind-Value="@TheValue" Indeterminate="@( !TheValue.HasValue )" />
<label for="DemoCheckbox">Checkbox</label>

@code{
    bool? TheValue { get; set; } // defaults to null so the checkbox will be indeterminate initially
}

Observe the behavior of the Indeterminate state


@*Observe the behavior of the Select all checkbox*@

<h3 class="text-muted">Deliveries</h3>

<div>
    <TelerikCheckBox Id="selectAllCheckbox"
                     Value="SelectAll"
                     ValueChanged="((bool newVal) => ChangeAllHander(newVal))"
                     Indeterminate="SelectAllIndeterminate"></TelerikCheckBox>
    <label for="selectAllCheckbox" class="text-muted">Select all items</label>
</div>

@foreach (var delivery in Deliveries)
{
    <div class="ml-2">
        <label class="text-muted">
            <TelerikCheckBox Value="delivery.IsDelivered"
                             ValueChanged="((bool value) => ChangeHandler(value, delivery.ProductName))" />
            @delivery.ProductName
        </label>
    </div>
}

@if (AlreadyDelivered.Any())
{
    <div>
        <h6 class="text-info">Successfully delivered products:</h6>
        <ul>
            @{
                foreach (var item in AlreadyDelivered)
                {
                    <li>
                        @item.ProductName
                    </li>
                }
            }
        </ul>
    </div>
}


@code {
    public bool SelectAll
    {
        get
        {
            return Deliveries.All(item => item.IsDelivered);
        }
    }

    public bool SelectAllIndeterminate
    {
        get
        {
            return Deliveries.Any(item => item.IsDelivered) && !SelectAll;
        }
    }

    public List<Delivery> Deliveries { get; set; }
    public List<Delivery> AlreadyDelivered
    {
        get
        {
            return Deliveries.Where(x => x.IsDelivered == true).ToList();
        }
    }

    void ChangeAllHander(bool newVal)
    {
        Deliveries.ForEach(item => item.IsDelivered = newVal);
    }

    void ChangeHandler(bool value, string productName)
    {
        var item = Deliveries.Where(x => x.ProductName == productName).First();
        item.IsDelivered = value;
    }

    //In real case scenarios the model will be in a separate file.
    public class Delivery
    {
        public string ProductName { get; set; }
        public bool IsDelivered { get; set; }
    }

    //Generating dummy data
    protected override void OnInitialized()
    {
        //Make your real data generation here.
        Deliveries = new List<Delivery>();
        Deliveries.Add(new Delivery()
        {
            ProductName = "PC",
            IsDelivered = false
        });
        Deliveries.Add(new Delivery()
        {
            ProductName = "Mobile Phone",
            IsDelivered = false
        });
        Deliveries.Add(new Delivery()
        {
            ProductName = "Headset",
            IsDelivered = false
        });
        Deliveries.Add(new Delivery()
        {
            ProductName = "Monitor",
            IsDelivered = false
        });
    }
}

The result from the code snippet above

gif to showcase the Indeterminate state

See Also

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