普通情况下，APP 随着用户拿手机是横向还是竖向，自动翻转 -- 当然，这个也需要用户设置手机的屏幕是否跟随手机的物理方向而翻转。

但如果我们的APP，在某种情况下，必须以竖屏方式显示，在某种情况下，必须以横屏方式显示，不管用户是否把手机横过来放。该怎么办？

网上搜了一堆东西出来。安卓的资料比较多一点，iOS 的就很少了。最终解决了这个问题。大概代码如下：

uses {$IFDEF IOS}iOSapi.UIKit{$ENDIF};

-----------------------------

procedure LockOrientations_iOS(ATo: TScreenOrientation; APossibles: TScreenOrientations);

{$IFDEF IOS}

var

  win : UIWindow;

  App : UIApplication;

  new : UIViewController;

  old : UIViewController;

  toio: UIInterfaceOrientation;

{$ENDIF}

begin

{$IFDEF IOS}

  Application.FormFactor.Orientations := [];

  App := TUIApplication.Wrap(TUIApplication.OCClass.sharedApplication);

  win := TUIWindow.Wrap(App.windows.objectAtIndex(0));

  case ATo of

    TScreenOrientation.Portrait: toio := UIInterfaceOrientationPortrait;

    TScreenOrientation.Landscape: toio := UIInterfaceOrientationLandscapeLeft;

    TScreenOrientation.InvertedLandscape: toio := UIInterfaceOrientationLandscapeRight;

    else //TScreenOrientation.InvertedPortrait

      toio := UIInterfaceOrientationPortraitUpsideDown;

  end;

  App.setStatusBarOrientation(toio);

  Application.FormFactor.Orientations := APossibles;

  new := TUIViewController.Wrap(TUIViewController.alloc.init);

  old := win.rootViewController;

  Win.setRootViewController(new);

  Win.makeKeyAndVisible;

  win.setRootViewController(old);

  win.makeKeyAndVisible;

{$ENDIF}

end;

----------------------

function ChangeScreenOrientation(const AIsLandscap: Boolean = true): Integer;

function ChangeScreenOrientation(const AIsLandscap: Boolean = true): Integer;

var

  ScreenService: IFMXScreenService;

  OrientSet: TScreenOrientations;

{$IFDEF IOS}

  screenSet: TScreenOrientation;

{$ENDIF}

begin

{$IFDEF ANDROID}

  //强制横屏。这段代码对安卓有用。网上看到的说法是对 iOS 无用。需要对 iOS 进行测试。pcplayer

  if TPlatformServices.Current.SupportsPlatformService(IFMXScreenService, IInterface(ScreenService)) then

  begin

    if AIsLandscap then //横屏显示

      OrientSet := [TScreenOrientation.soLandscape]

    else

      OrientSet := [TScreenOrientation.Portrait];

    ScreenService.SetScreenOrientation(OrientSet);

  end;

{$ENDIF}

{$IFDEF IOS}

  if AIsLandscap then //横屏显示

  begin

    OrientSet := [TScreenOrientation.soLandscape];

    screenSet := TScreenOrientation.Landscape;

  end

  else

  begin

    OrientSet := [TScreenOrientation.Portrait];

    screenSet := TScreenOrientation.Portrait;

  end;

  LockOrientations_iOS(screenSet, OrientSet);

{$ENDIF}

end;

使用：程序调用 ChangeScreenOrientation 这个方法，可以设置横屏或竖屏。iOS 和 Android 都可以。