<pre><code>
@interface FileViewController :QLPreviewController

@end

@implementation FileViewController

<p>- (void)viewDidLoad {
<p> [super viewDidLoad];
<p> self.navigationItem.leftBarButtonItem = newBackButton;
<p>
<p>// [self.navigationItem setHidesBackButton:YES] 无效
<p> [self.navigationItem setHidesBackButton:YES animated:NO];//必须的，不然。。。
<p>}

@end