Order the CheckBox states

Environment

Product Version 2019.3 1119.1
Product Checkbox for Xamarin

Description

By default the logic of the RadCheckBox IsChecked state when IsThreeState = "True" is Indeterminate -> Unchecked -> Checked. For sure there will be some scenarios when you want to change the state flow, for example Indeterminate -> Checked -> Unchecked.

In this help article we will show you how this could be achieved.

Solution

The CheckBox IsChecked state flow can be changed inside the RadCheckBox IsCheckedChanged event.

  1. Create a ViewModel class with property that will be bind to the CheckBox IsChecked property.

        public class ViewModel : NotifyPropertyChangedBase
    {
        private bool? myproperty;
        public bool? MyProperty 
        {
            get
            {
                return this.myproperty;
            }
            set
            {
                if(this.myproperty != value)
                {
                    this.myproperty = value;
                    OnPropertyChanged();
                }
            }
        }
    }
    ```
    
    1. then inside the code behind create a bool property that will be used to trigger whether the checkbox state is changed and inside the RadCheckBox_IscheckedChanged event implement a custom logic for changing the state:
        public partial class MainPage : ContentPage
    {
        ViewModel vm;
    
    
    
        public MainPage()
        {
            InitializeComponent();
    
            this.vm = new ViewModel();
            this.BindingContext = vm;
        }
        private bool isinternalchanged = true;
        public bool IsInternalChanged
        {
            get
            {
                return this.isinternalchanged;
            }
    
            set
            {
                if (this.isinternalchanged)
                {
                    return;
                }
            }
        }
        private void RadCheckBox_IsCheckedChanged(object sender, Telerik.XamarinForms.Primitives.CheckBox.IsCheckedChangedEventArgs e)
        {
            var obj = sender as RadCheckBox;
            var old = e.OldValue;
    
            if (this.isinternalchanged)
            {
                this.isinternalchanged = false;
                return;
            }
    
            if(old == null)
            {
                this.isinternalchanged = true;
                vm.MyProperty = true;
            }
    
            else if(old == true)
            {
                this.isinternalchanged = true;
                vm.MyProperty = false;
            }
    
            else if(old == false)
            {
                this.isinternalchanged = true;
                vm.MyProperty = null;
            }
        }
    }
    ```
    
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