How to reset Calendar Extender for Ajax Control Toolkit to its default value which should be empty string (server side)?

How to reset Calendar Extender for Ajax Control Toolkit to its default value which should be empty string? Reset 开发者_如何学Goto be server side.

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You must reset both calendar extender and its target control (textbox).

        txtProductionDate.Text = string.Empty;
        calExtProductionDate.SelectedDate = null;