直接上代碼：

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    
    if([[UIDevice currentDevice] respondsToSelector:@selector(setOrientation:)]) {
        
        SEL selector = NSSelectorFromString(@"setOrientation:");
        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[UIDevice instanceMethodSignatureForSelector:selector]];
        [invocation setSelector:selector];
        [invocation setTarget:[UIDevice currentDevice]];
        
        NSInteger val = UIInterfaceOrientationLandscapeLeft;//橫屏
        [invocation setArgument:&val atIndex:2];
        [invocation invoke];
        
    }
}