When to use layoutSubview in iOS

I am writing iOS application for iPad that require custom layout.

The layout from portrait and landscape are totally difference, so it can't be solve by using UIAutoResizingMask.

I try to use the layoutSubview Method, but I detected that layout subview is called a lot (from UIScrollView). How can i redu开发者_StackOverflow中文版ce the layoutSubview call to optimize the code , or I should call it by my self when ever the device is rotated.

Thank.

For different landscape and portrait design use view controllers methods such as

-(void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration;
-(void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation;
-(void)willAnimateRotationToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration;

If you create your custom view depending on current orientation, check this orientation by UIDeviceOrientationDidChangeNotification notification and write appropriate code.

in one of the init~ methods:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(didChangedOrientation:) name:UIDeviceOrientationDidChangeNotification object:nil];

And action

- (void) didChangedOrientation:(NSNotification *)sender{
UIDeviceOrientation orientation = [[UIDevice currentDevice] orientation];
if (UIDeviceOrientationIsPortrait(orientation)){}}

The fact that layoutSubviews gets called by a child UIScrollView is very unfortunate, but there's an (ugly) workaround:

@interface MyClass : UIView {
    BOOL reallyNeedsLayout_;
}
@end

@implementation MyClass

- (void)setNeedsLayout
{
    [super setNeedLayout];
    reallyNeedsLayout_ = YES;
}

- (void)setFrame:(CGRect)rect
{
    [super setFrame:rect];
    reallyNeedsLayout_ = YES;
}

- (void)layoutSubviews
{
    if (!reallyNeedsLayout_) return;
    reallyNeedsLayout_ = NO;

    // Do layouting.
}
@end

Not the best solution but seems to work reasonably well.

You should not do expensive calculations in layoutSubviews:

Speaking from experience I would personally only adjust your layout based upon deviceDidRotateSelector notifications. I have an updatePortrait method and an updateLandscape method and call whichever is necessary.