LoginViewController *loginViewController =[[ LoginViewController alloc] init];
UINavigationController *nav=[[UINavigationController alloc]initWithRootViewController:loginViewController];
UIButton *leftBtn = [UIButton buttonWithType:UIButtonTypeCustom];
leftBtn.frame = CGRectMake(0, 0, 70, 37);leftBtn.titleLabel.font=[UIFont systemFontOfSize:25.0];
[leftBtn setTitle:@"取消" forState:UIControlStateNormal];
[leftBtn addTarget:self action:@selector(dismissController) forControlEvents:UIControlEventTouchUpInside];
loginViewController.navigationItem.leftBarButtonItem =[[UIBarButtonItem alloc] initWithCustomView:leftBtn];
[self.navigationController presentViewController:nav animated:YES completion:nil];