设备方向改变时以编程方式重绘视图的简单方法

Question

I'm new to iOS development and for my assignment, I'm tasked changing updating the ViewController programmatically when the device's orientation changes. I've found a snippet of an answer here, but it doesn't get the job done.

I tried adding this to the viewWillLayoutSubviews of my View Controller, but all I get is an unused variable warning.

CGRect rotatedFrame = [self.view convertRect:self.view.frame fromView:self.view.superview];

viewWillLayoutSubviews and rotation

As a "hint", I've been told it's simple to implement in viewWillLayoutSubviews . Going through and changing all the CGRects in my VC doesn't sound like a couple of lines of code. There's got to be a simpler, more efficient way to do this, but I've only found snippets of solutions digging around on this site. Thanks for reading.

Answer 1

The line of code you are using is assigning a CGRect to the rotatedFrame variable, it's not updating anything on your view controller.

There's many ways to approach this but it depends on what is contained in your view and how it's been configured. Things like Auto Layout for example could let you configure almost everything in Interface Builder and let you avoid doing most things in code.

You've been tasked to do this programatically and since we know that viewWillLayoutSubviews is called every time the device is rotated that's a good place to start. Here's a lazy way I've gone about rotating a video to fit a new orientation using a transformation:

//Vertical
CGSize size = self.view.frame.size;
someView.transform = CGAffineTransformMakeRotation((M_PI * (0) / 180.0))
someView.frame = CGRectMake(0, 0, MIN(size.width, size.height), MAX(size.width, size.height));

//Horizontal
CGSize size = [UIScreen mainScreen].bounds.size;
int directionModifier = ([UIDevice currentDevice].orientation == UIInterfaceOrientationLandscapeLeft) ? -1 : 1;
someView.bounds = CGRectMake(0, 0, MAX(size.width, size.height), MIN(size.width, size.height));
someView.transform = CGAffineTransformMakeRotation((M_PI * (90) / 180.0) *directionModifier);
someView.transform = CGAffineTransformTranslate(someView.transform,0,0);

How many subviews are in your view? Are they grouped? If you're using auto-resizing masks you might get away with only adjusting the frames of one or two views. If your root view has a number of subviews you can loop through views that need similar adjustments to avoid having to write excess code. It really depends on how everything has been set up.

Answer 2

I figured out how to determine the viewWidth and viewHeight and set those as CGFloats. I then added an if-else statement which figures out if the display is in portrait or landscape and sets the problematic calculateButton accordingly.

Apologies for lengthy code, but I've found in searching this site I find "snippets" of answers, but being new to iOS it's difficult to figure out what goes where. Hopefully, this helps someone later. (and hopefully it's correct)

- (void) viewWillLayoutSubviews {
    [super viewWillLayoutSubviews];

    CGFloat viewWidth = self.view.bounds.size.width;
    CGFloat viewHeight = self.view.bounds.size.height;
    CGFloat padding = 20;
    CGFloat itemWidth = viewWidth - padding - padding;
    CGFloat itemHeight = 44;

// Bunch of setup code for layout items

    // HOMEWORK: created if-else statement to deal w/ portrait vs. landscape placement of calculateButton.

    if (viewWidth > viewHeight) {
        // portrait
        CGFloat bottomOfLabel = viewHeight;
        self.calculateButton.frame = CGRectMake(padding, bottomOfLabel - itemHeight, itemWidth, itemHeight);
    } else {
        // landscape
        CGFloat bottomOfLabel = CGRectGetMaxY(self.resultLabel.frame);
        self.calculateButton.frame = CGRectMake(padding, bottomOfLabel + padding, itemWidth, itemHeight);
    }
}