UIButton* backButton = [UIButton buttonWithType:101]; // left-pointing shape!
[backButton setTitle:@"更多" forState:UIControlStateNormal];
[backButton addTarget:self action:@selector(btBackPressed:) forControlEvents:UIControlEventTouchUpInside];
UIBarButtonItem* tempBar=[[UIBarButtonItem alloc]initWithCustomView:backButton];
self.navigationItem.leftBarButtonItem=tempBar;