用处：实现一个web浏览器，加载静态html，动态url，调用js
//加载动态url
self.webView = [[UIWebView alloc]initWithFrame:self.view.bounds];
NSString *str = @"http://www.baidu.com";
NSURL *url = [NSURL URLWithString:str];
NSURLRequest *request = [NSURLRequest requestWithURL:url];
[self.webView loadRequest: request];