You can pass the Page ViewState object to the InputPasswordStrengthSettings constructor.
The constructor basically awaits ViewState object where it can save it settings. Since in your case the InputPasswordStrengthSettings is used outside of RadControl we cannot pass the control ViewState. Instead, we can initialize it with a StateBag supplied from the page object.
protected void Page_Load(EventArgs e)
var b = new RadDateInput();
var settings = new InputPasswordStrengthSettings(this.ViewState);
I hope that this helps.
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