ios - Lazy loading in UITableView crashes app -

i using uitableview customcell. customcell contains uiimageview , 2 uilabel. in uiimageview want load image url , want save in document directory.

here code tried,

nsarray *paths = nssearchpathfordirectoriesindomains(nsdocumentdirectory,nsuserdomainmask, yes); nsstring *documentsdirectory = [paths objectatindex:0]; nsstring *savedimagepath = [documentsdirectory stringbyappendingpathcomponent:[urlarr objectatindex:indexpath.row]];//arr nsmutablearray of image url  uiimage *img1 = [uiimage imagewithcontentsoffile:savedimagepath]; if (!img1 || [uiimagepngrepresentation(img1) length] <=0) {     id path =[urlarr objectatindex:indexpath.row];     path = [path stringbyreplacingoccurrencesofstring:@" " withstring:@"%20"];     nsurl *url = [nsurl urlwithstring:path];     nsmutablearray *arr = [[nsmutablearray alloc] initwithobjects:url, [nsstring stringwithformat:@"%d", indexpath.row+1], nil ];      [self performselectorinbackground:@selector(loadimageinbackground:) withobject:arr];  } 

and 1 too.

//—————————————-lazy loading———————– - (void)loadimageinbackground:(nsarray *)urlandtagreference {         nsdata *imgdata = [nsdata datawithcontentsofurl:[urlandtagreference objectatindex:0]];         uiimage *imgload = [[uiimage alloc] initwithdata:imgdata];          nsmutablearray *arr = [[nsmutablearray alloc] initwithobjects:imgload, [urlandtagreference objectatindex:1], nil];          [self performselectoronmainthread:@selector(assignimagetoimageview:) withobject:arr waituntildone:yes]; }  - (void) assignimagetoimageview:(nsarray *)imgandtagreference {          nsarray *paths = nssearchpathfordirectoriesindomains(nsdocumentdirectory,nsuserdomainmask, yes);          nsstring *documentsdirectory = [paths objectatindex:0];          nsstring *savedimagepath = [documentsdirectory stringbyappendingpathcomponent:[urlarr objectatindex:[[imgandtagreference objectatindex:1] intvalue]-1]];           uiimage* imagetosave = savedimagepath;          nsdata *imagedata = uiimagepngrepresentation(imagetosave);          [imagedata writetofile:savedimagepath atomically:no];  } 

reason crashing shows nsinvalidargumentexception. image not showing in uitableviewcell. appreciated.

for lazy loading of table view images there few options available. can make use of them in design save time , avoid efforts reinvent wheel.
1. apple lazy loading code --link
2. sdwebimage --link

cheers! amar.