通过绑定添加最初缺少的集合项

Given:

class StringRecord : INotifyPropertyChanged
{
    public string Key   { get; set; } // real INPC implementation is omitted
    public string Value { get; set; } // real INPC implementation is omitted
    ...
}

class Container
{
    public ObservableKeyedCollection<string, StringRecord> Params { get; set; }
    ...
{
class StringRecord : INotifyPropertyCh