It is possible that this is a once asked question. Still, before working with any platform, you need at least a little acquaintance with it and its capabilities. In particular, events accept the delegate to the calling function, and not some kind of true. Assigning true is generally something incomprehensible and going beyond simple logic.
All right, your business, simply more difficult code you do not write at random and to prompt with such level of understanding very few people will undertake. Essentially, everything is simple:
public MainWindow() { InitializeComponent(); ΠΊΠ½ΠΎΠΏΠΊΠ°.Click += new RoutedEventHandler(func_Click); } void func_Click(object sender, RoutedEventArgs args) { ΡΠ΅ΠΊΠ±ΠΎΠΊΡ.IsChecked = true; }