所有视图都是竖屏，一个ViewController需要强制转换横屏

1.info.plist 里Supported interface orientations添加横屏和竖屏的方向。（在Target里打钩也可以）

2.在self.window的rootViewController类里写下面三个方法:(因为我所有视图都是竖屏不支持旋转的，所以关闭了自动旋转)

- (BOOL)shouldAutorotate

{

    return NO;

}

- (NSUInteger)supportedInterfaceOrientations

{

    return UIInterfaceOrientationMaskAll;

}

- (UIInterfaceOrientation)preferredInterfaceOrientationForPresentation

{

    return UIInterfaceOrientationPortrait;

}

3.在需要旋转横屏的ViewController里，写下面的代码

//先恢复原状

    self.view.transform =
CGAffineTransformIdentity;

    //隐藏导航栏

    self.navigationController.navigationBarHidden =
YES;

    //隐藏状态栏

    [UIApplication
sharedApplication].statusBarHidden =
YES;

        

    //设置bounds

    self.view.bounds
= CGRectMake(0,
0, HDScreenWidth,
HDScreenHeight);

    //旋转view

    [self.view
setTransform:CGAffineTransformMakeRotation(M_PI/2)];

    

    //设置状态栏方向，超级重要。（只有设置了这个方向，才能改变弹出键盘的方向）

    [[UIApplication
sharedApplication] setStatusBarOrientation:UIInterfaceOrientationLandscapeRight];

私有API，设置设备方向。

//设置状态栏横屏

    [[UIApplication
sharedApplication] setStatusBarOrientation:UIInterfaceOrientationLandscapeRight];

//    [[UIDevice currentDevice] setValue:[NSNumber numberWithInteger:UIDeviceOrientationPortrait] forKey:@"orientation"];//这句话是防止手动先把设备置为横屏,导致下面的语句失效.
   
if ([[UIDevice
currentDevice] respondsToSelector:@selector(setOrientation:)]) {

        [[UIDevice
currentDevice] performSelector:@selector(setOrientation:)
withObject:@(UIInterfaceOrientationLandscapeRight)];
    }