对于iPad分割窗口，[[UIScreen mainScreen] bounds]不起作用，使用[UIApplication sharedApplication].delegate.window.bounds代替。

对于iPad分割窗口，[[UIScreen mainScreen] bounds]不起作用，使用[UIApplication sharedApplication].delegate.window.bounds代替。

这是非常非常容易得到你的设备大小，以及考虑方向:

// grab the window frame and adjust it for orientation
UIView *rootView = [[[UIApplication sharedApplication] keyWindow] 
                                   rootViewController].view;
CGRect originalFrame = [[UIScreen mainScreen] bounds];
CGRect adjustedFrame = [rootView convertRect:originalFrame fromView:nil];

注意，[UIScreen mainScreen]包含状态栏，如果你想检索你的应用程序的框架(不包括状态栏)，你应该使用

+ (CGFloat) window_height   {
    return [UIScreen mainScreen].applicationFrame.size.height;
}

+ (CGFloat) window_width   {
    return [UIScreen mainScreen].applicationFrame.size.width;
}

iOS 13+的答案(找到键窗口的代码来源):

guard let window = UIApplication.shared.windows.first(where: { $0.isKeyWindow }) else {
    return
}

let windowWidth = window.frame.width
let windowHeight = window.frame.height

我以前用过这些方便的方法:

- (CGRect)getScreenFrameForCurrentOrientation {
    return [self getScreenFrameForOrientation:[UIApplication sharedApplication].statusBarOrientation];
}

- (CGRect)getScreenFrameForOrientation:(UIInterfaceOrientation)orientation {

    CGRect fullScreenRect = [[UIScreen mainScreen] bounds];

    // implicitly in Portrait orientation.
    if (UIInterfaceOrientationIsLandscape(orientation)) {
      CGRect temp = CGRectZero;
      temp.size.width = fullScreenRect.size.height;
      temp.size.height = fullScreenRect.size.width;
      fullScreenRect = temp;
    }

    if (![[UIApplication sharedApplication] statusBarHidden]) {
      CGFloat statusBarHeight = 20; // Needs a better solution, FYI statusBarFrame reports wrong in some cases..
      fullScreenRect.size.height -= statusBarHeight;
    }

    return fullScreenRect;
}