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;
           }
       }
   }
   ```