ios - UIWebView displaying as a white screen -

in app, have view controller contains uiwebview. view controller has uiwebview iboutlet. when loading view white screen navigation bar @ top. here code loading uiwebview. completeurl wasn't being formatted correctly , null. no information can scour through online seems able me issue.

-(void) viewwillappear:(bool)animated {     nsstring *stringurl = [nsstring stringwithformat:@"www.ncbi.nlm.nih.gov/pubmed/?term=%@", _url];     nsurl *completeurl = [nsurl urlwithstring: [stringurl stringbyaddingpercentescapesusingencoding: nsutf8stringencoding]];     nsurlrequest *request = [nsurlrequest requestwithurl:completeurl];     [_webview loadrequest:request];     nslog(@"%@", request); } 

once check line may problem here replace once , check it,

nsstring *stringurl = [nsstring stringwithformat:@"http://www.ncbi.nlm.nih.gov/pubmed?term=%@", _url];