CheckBox values / no MVVM Xamarin - xamarin

Question

I have a group of check boxes and i need them to change value.. if one is checked the other should be unchecked. The reason why dont want to implement MVVM is that this is just new frontend for already existing application, i just need these to work before we merge projects. This what i have and it doesnt work,i get null reference / System.NullReferenceException: 'Object reference not set to an instance of an object.'
I have this in my code
private void AdvancedCheckBox_IsCheckedChanged(object sender, IsCheckedChangedEventArgs e)
{
if (AdvancedCheckBox.IsChecked == true) //System.NullReferenceException: 'Object reference not set to an instance of an object.'
{
AllCheckBox.IsChecked = false;
UpperIntermediateCheckBox.IsChecked = false;
AdvancedCheckBox.IsChecked = false;
}
else
AdvancedCheckBox.IsChecked = true;
}
private void UpperIntermediateCheckBox_IsCheckedChanged(object sender, IsCheckedChangedEventArgs e)
{
if (UpperIntermediateCheckBox.IsChecked == true)
{
AllCheckBox.IsChecked = false;
UpperIntermediateCheckBox.IsChecked = false;
AdvancedCheckBox.IsChecked = false;
}
else
UpperIntermediateCheckBox.IsChecked = true;
}
private void IntermediateCheckBox_IsCheckedChanged(object sender, IsCheckedChangedEventArgs e)
{
CheckBox IntermediateCheckBox = sender as CheckBox;
if (IntermediateCheckBox.IsChecked == false)
{
AllCheckBox.IsChecked = false;
UpperIntermediateCheckBox.IsChecked = false;
AdvancedCheckBox.IsChecked = false ;
}
else
IntermediateCheckBox.IsChecked = true ;
}
private void AllCheckBox_IsCheckedChanged(object sender, IsCheckedChangedEventArgs e)
{
CheckBox AllCheckBox = sender as CheckBox;
if (AllCheckBox.IsChecked == true) System.NullReferenceException: 'Object reference not set to an instance of an object.'
{
UpperIntermediateCheckBox.IsChecked = false;
AdvancedCheckBox.IsChecked = false;
IntermediateCheckBox.IsChecked = false;
}
else
AllCheckBox.IsChecked = true;
}
and my xaml
<StackLayout Grid.Row="0"
Orientation="Horizontal"
Spacing="10"
HorizontalOptions="Start">
<grial:Checkbox x:Name="AllCheckBox"
IsCheckedChanged ="AllCheckBox_IsCheckedChanged"
HorizontalOptions="Start">
<Label
Margin="10,0"
FontSize="19"
Text="{ grial:Translate A_LabelAllArticles}"
VerticalOptions="Center"
TextColor="{ DynamicResource AccentColor }" />
</grial:Checkbox>
</StackLayout>
<StackLayout Grid.Row="1"
Orientation="Horizontal"
Spacing="10"
HorizontalOptions="Start">
<grial:Checkbox x:Name="BeginnerCheckBox"
IsChecked="false"
HorizontalOptions="Start">
<Label
FontSize="19"
Margin="10,0"
Text="{ grial:Translate A_LabelBeginnerArticles}"
VerticalOptions="Center"
TextColor="{ DynamicResource AccentColor }" />
</grial:Checkbox>
</StackLayout>
<StackLayout Grid.Row="2"
Orientation="Horizontal"
Spacing="10"
HorizontalOptions="Start">
<grial:Checkbox x:Name="IntermediateCheckBox"
IsCheckedChanged="IntermediateCheckBox_IsCheckedChanged"
HorizontalOptions="Start">
<Label
FontSize="19"
Margin="10,0"
Text="{ grial:Translate A_LabelIntermediateArticles}"
VerticalOptions="Center"
TextColor="{ DynamicResource AccentColor }" />
</grial:Checkbox>
</StackLayout>
<StackLayout Grid.Row="3"
Orientation="Horizontal"
Spacing="10"
HorizontalOptions="Start">
<grial:Checkbox x:Name="UpperIntermediateCheckBox"
IsCheckedChanged="UpperIntermediateCheckBox_IsCheckedChanged"
HorizontalOptions="Start">
<Label
FontSize="19"
Margin="10,0"
Text="{ grial:Translate A_LabelUpperIntermediateArticles}"
VerticalOptions="Center"
TextColor="{ DynamicResource AccentColor }" />
</grial:Checkbox>
</StackLayout>
<StackLayout Grid.Row="4"
Orientation="Horizontal"
Spacing="10"
HorizontalOptions="Start">
<grial:Checkbox x:Name="AdvancedCheckBox"
IsCheckedChanged="AdvancedCheckBox_IsCheckedChanged"
HorizontalOptions="Start">
<Label
FontSize="19"
Margin="10,0"
Text="{ grial:Translate A_LabelAdvancedArticles}"
VerticalOptions="Center"
TextColor="{ DynamicResource AccentColor }" />
</grial:Checkbox>

Answer 1

You are using a Checkbox from the Grial UIKit, but are defining the sender as the Native Xamarin.Forms CheckBox, use the Grial CheckBox as the Casting Class of the sender
//This will make every checkbox to checked or unchecked depending of the state of the clicked one
private void AllCheckBox_IsCheckedChanged(object sender, IsCheckedChangedEventArgs e)
{
CheckBox ClickedCheckbox = sender as UXDivers.Grial.Checkbox;
ChangeAllCheckboxesTo(ClickedCheckbox.IsChecked != null ? ClickedCheckbox.IsChecked : false);
}
//This will make every checkbox to false if you select one
private void AnyCheckBox_IsCheckedChanged(object sender, IsCheckedChangedEventArgs e)
{
CheckBox ClickedCheckbox = sender as UXDivers.Grial.Checkbox;
bool WasSelected = ClickedCheckbox.IsChecked != null ? ClickedCheckbox.IsChecked != null : false;
ChangeAllCheckboxesTo(false);
if(!WasSelected)
ClickedCheckbox.IsChecked = true;
}
public void ChangeAllCheckboxesTo(bool value)
{
try
{
UpperIntermediateCheckBox.IsChecked = value;
AdvancedCheckBox.IsChecked = value;
IntermediateCheckBox.IsChecked = value;
}
catch(Exception ex)
{
}
}