强制横屏

-(UIInterfaceOrientationMask)supportedInterfaceOrientations

{

    return UIInterfaceOrientationMaskAllButUpsideDown;

}

- (UIInterfaceOrientation)preferredInterfaceOrientationForPresentation

{

    return UIInterfaceOrientationPortrait;

}

-(BOOL)shouldAutorotate

{

    return self.isON;

}

返回到上一个页面的时候进行一些处理，否则导致上一个页面也变成了横屏状态：这个时候要在viewWillDisappear方法里面添加如下代码：

 ison=!ison;

        if (ison==YES)

        {

            [self forceOrientation:UIInterfaceOrientationPortrait];

        }else{

            [self forceOrientation:UIInterfaceOrientationLandscapeRight];

        }

        

        

    }

    

}

- (void)forceOrientation: (UIInterfaceOrientation)orientation {

    if ([[UIDevice currentDevice] respondsToSelector:@selector(setOrientation:)]) {

        SEL selector = NSSelectorFromString(@"setOrientation:");

        NSInvocation *invocation = [NSInvocation invocationWithMethodSignature:[UIDevice instanceMethodSignatureForSelector:selector]];

        [invocation setSelector:selector];

        [invocation setTarget: [UIDevice currentDevice]];

        int val = orientation;

        [invocation setArgument:&val atIndex:2];

        [invocation invoke];

    }

}

其实viewWillDisappear代码也就是强制转成竖屏的意思，特别要注意的是 int val = UIInterfaceOrientationPortrait; 这句代码。