WPF 复选框内容不正确

标题：WPF 复选框内容不正确

C#
// 数据源
public class ViewModel : INotifyPropertyChanged
{
    private bool _isChecked;
    public bool IsChecked
    {
        get { return _isChecked; }
        set
        {
            if (_isChecked != value)
            {
                _isChecked = value;
                OnPropertyChanged(nameof(IsChecked));
            }
        }
    }
    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}
// XAML
    
// 代码-behind
private void SetIsChecked()
{
    ViewModel.IsChecked = true;
}
// 使用绑定器
public class ViewModel : INotifyPropertyChanged
{
    private bool _isChecked;
    public bool IsChecked
    {
        get { return _isChecked; }
        set
        {
            if (_isChecked != value)
            {
                _isChecked = value;
                OnPropertyChanged(nameof(IsChecked));
            }
        }
    }
    public ViewModel()
    {
        BindingOperations.EnableCollectionSynchronization(this, new object());
    }
    public event PropertyChangedEventHandler PropertyChanged;
    protected virtual void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}