how to validate custom web part property? [duplicate]

Question

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How to validate Web Part property value?

below is a custom prop and a code that i am using for my custom web part, my question is, how to validate a custom web part and my requirement is that, when the user enter WebPartContentLink link i want to make sure that it starts with http:// any idea how to implement ?

private string _webPartContentLink = null;
 [Personalizable(PersonalizationScope.Shared)]
        [WebBrowsable(true)]
        [System.ComponentModel.Category("Services")]
        [WebDisplayName("Enter WebPart Content Link")]
        [WebDescription("Enter WebPart Content Link")]
        public string WebPartContentLink 
        {
            get
            {
                if (_webPartContentLink == null)
                {
                    _webPartContentLink = string.Empty;
                }
                return _webPartContentLink;
            }
            set 
                {

                    _webPartContentLink = value;
                }
          }



PageViewerWebPart oWebPart = new PageViewerWebPart();
oWebPart.ContentLink = WebPart.WebPartContentLink.ToString();
Controls.Add(oWebPart);