Event Binding in Viewmodel for Checkbox

[Matthew Bailey]

I have a pair of Checkboxes that need their respective values for IsChecked to be opposite.

CheckBoxA = IsChecked ~~~ CheckBoxB = !IsChecked

They should toggle eachother, and I had that managed with Xamarin's standard Checkbox object by attaching Triggers, but when I try to write a Trigger on SfCheckBox Visual Studio gives me an error that it doesn't exist.

Can someone help me figure out how to set triggers or utilize StateChanged through a ViewModel Binding?

[Rachel A]

Hi Matthew, 

  

Greetings from Syncfusion. 

 

We have prepared sample to achieve your requirement by using view model property binding and Event Triggers. The sample can be downloaded from the below location. 

  

Sample: https://www.syncfusion.com/downloads/support/directtrac/general/ze/SimpleChkBox_Trigger2117973420.zip  

  

Solution 1: Using the MVVM pattern (Property Binding) 

[XAML] 

  <sfButtons:SfCheckBox x:Name="CheckBox1" Text="Combo 1" IsChecked="{Binding IsCheckBox1Checked}" Grid.Row="1" Grid.Column="0" Margin="10,0,20,0"/> 

  <sfButtons:SfCheckBox x:Name="CheckBox2" Text="Combo 2" IsChecked="{Binding IsCheckBox2Checked}" Grid.Row="1" Grid.Column="1" Margin="20,0,10,0"/> 

  

Change the checked value based on another checked property value like below: 

[C#] 

        private bool chk_CheckBox1; 

        private bool chk_CheckBox2; 

        public bool IsCheckBox1Checked 

        { 

            get { return chk_CheckBox1; } 

            set 

            { 

                chk_CheckBox1 = value; 

                if (chk_CheckBox1) 

                    IsCheckBox2Checked = false; 

                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("IsCheckBox1Checked")); 

            } 

        } 

        public bool IsCheckBox2Checked 

        { 

            get { return chk_CheckBox2; } 

            set 

            { 

                chk_CheckBox2 = value; 

                if (chk_CheckBox2) 

                    IsCheckBox1Checked = false; 

                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs("IsCheckBox2Checked")); 

            } 

        } 

  

Solution 2:  Event Triggers 

[XAML] 

                <sfButtons:SfCheckBox x:Name="CheckBox3" Text="Combo 3" Grid.Row="3" Grid.Column="0" Margin="10,0,20,0"> 

                    <sfButtons:SfCheckBox.Triggers> 

                        <EventTrigger Event="StateChanged"> 

                            <local:CheckStateValidationTriggerAction OpponentCheckBox="{x:Reference CheckBox4}"/> 

                        </EventTrigger> 

                    </sfButtons:SfCheckBox.Triggers> 

                </sfButtons:SfCheckBox> 

                <sfButtons:SfCheckBox x:Name="CheckBox4" Text="Combo 4" Grid.Row="3" Grid.Column="1" Margin="20,0,10,0"> 

                    <sfButtons:SfCheckBox.Triggers> 

                        <EventTrigger Event="StateChanged"> 

                            <local:CheckStateValidationTriggerAction OpponentCheckBox="{x:Reference CheckBox3}"/> 

                        </EventTrigger> 

                    </sfButtons:SfCheckBox.Triggers> 

                </sfButtons:SfCheckBox> 

  

Changing opponent checkbox state based on triggered check box state.  

[C#] 

  public class CheckStateValidationTriggerAction : TriggerAction<SfCheckBox> 

    { 

       public SfCheckBox OpponentCheckBox { get; set; } 

        protected override void Invoke(SfCheckBox checkbox) 

        { 

           if(OpponentCheckBox != null) 

            { 

                OpponentCheckBox.IsChecked = !checkbox.IsChecked; 

            } 

        } 

    } 

  

Regards, 

Rachel.