Guys, How can i make a TextBox as IsReadOnly="True" based on the item selected on the ComboBox? : I would be so greatful if you could help meee, thx!

HERE IS THE XAML

    <ComboBox Margin="8" Name="cmbox" SelectionChanged="cmbox_SelectionChanged" >
                            <ComboBoxItem IsSelected="True">ESCALONADO</ComboBoxItem>
                            <ComboBoxItem>INTEGRAL</ComboBoxItem>
                        </ComboBox>
    <TextBox IsReadOnly="{Binding Testcmb}" Grid.Column="1" Margin="8"/>

    
HERE IS A LITTLE BIT OF THE CODE BEHIND

I tried to attribute the value of the property Testcmb based on the selected item on the combobox, and then make the bindin to the textbox to turn it as a IsReadOnly="true". Is the sintax right?

    private void cmbox_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if(cmbox.SelectedIndex > 0)
            {
                (Object).Testcmb = true;
            }
            else
            {
                (Object).Testcmb = false;
            }
        }    

    
    private bool _testcmb;     
    public bool Testcmb
        {   
            get { return _testcmb; }
            set
            {
                if (this._testcmb != value)
                {
                    this._testcmb = value;
                    this.NotifyPropertyChanged("Testcmb");
                };
            }
        }
        public event PropertyChangedEventHandler PropertyChanged;
    
        public void NotifyPropertyChanged(string propName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propName));
            }
        }