检测网络图片存不存在的方法

先用
NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];  

判断一下当前的链接。
-(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
    NSHTTPURLResponse *httpResponse = (NSHTTPURLResponse *)response;
    if ((([httpResponse statusCode]/100) == 2)) {
        // self.earthquakeData = [NSMutableData data];
        [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
        
        [ webView loadRequest:[ NSURLRequest requestWithURL: myUrl ]];
        webView.delegate = self;
    } else {
        NSDictionary *userInfo = [NSDictionary dictionaryWithObject:
                                  NSLocalizedString(@"HTTP Error",
                                                    @"Error message displayed when receving a connection error.")
                                                             forKey:NSLocalizedDescriptionKey];
        NSError *error = [NSError errorWithDomain:@"HTTP" code:[httpResponse statusCode] userInfo:userInfo];
        
        if ([error code] == 404) {
            NSLog(@"网络图片不存在");
            webView.hidden = YES; //隐藏webView或者用本地默认图片代替
        }        
        
    }
}