目的
本示例代码的目的有两个：
- 理解屏幕旋转的时候，视图控制器所调用的方法的作用。
- 理解Masonry的基本使用。
实现后的效果 （不支持upside down方向）
screenRotating.gif
示例代码
// 1
// 屏幕旋转时调用
- (void) viewDidLayoutSubviews {
UIInterfaceOrientation orientation = [[UIApplication sharedApplication] statusBarOrientation];
switch (orientation) {
case UIInterfaceOrientationPortrait:
NSLog(@"portrait");
[self verticalTwoViews];
break;
case UIInterfaceOrientationLandscapeLeft:
NSLog(@"landscape left");
[self horizontalTwoViews];
break;
case UIInterfaceOrientationLandscapeRight:
NSLog(@"landscape right");
[self horizontalTwoViews];
break;
case UIInterfaceOrientationPortraitUpsideDown:
NSLog(@"portrait upside down");
break;
case UIInterfaceOrientationUnknown:
break;
default:
break;
}
}
// 两个视图垂直排列
- (void) verticalTwoViews {
if (self.leftView == nil) {
self.leftView = [[UIView alloc] initWithFrame:CGRectZero];
self.leftView.backgroundColor = [UIColor redColor];
[self.view addSubview:self.leftView];
self.leftLabel = [[UILabel alloc] initWithFrame:CGRectZero];
[self.leftView addSubview:self.leftLabel];
self.leftLabel.numberOfLines = 0;
self.leftLabel.backgroundColor = [UIColor whiteColor];
self.leftLabel.text = @"揭谛揭谛波罗揭谛波罗僧揭谛菩提娑婆诃";
// 2
[self.leftLabel setContentCompressionResistancePriority:1 forAxis:UILayoutConstraintAxisHorizontal];
[self.leftLabel mas_makeConstraints:^(MASConstraintMaker * make) {
make.top.left.right.equalTo(self.leftView).mas_offset(UIEdgeInsetsMake(20, 20, 0, 20)).priorityMedium();
}];
}
if (self.rightView == nil) {
self.rightView = [[UIView alloc] initWithFrame:CGRectZero];
self.rightView.backgroundColor = [UIColor blueColor];
[self.view addSubview:self.rightView];
self.rightLabel = [[UILabel alloc] initWithFrame:CGRectZero];
[self.rightView addSubview:self.rightLabel];
self.rightLabel.numberOfLines = 0;
self.rightLabel.backgroundColor = [UIColor whiteColor];
self.rightLabel.text = @"揭谛揭谛波罗揭谛波罗僧揭谛菩提娑婆诃";
[self.rightLabel setContentCompressionResistancePriority:1 forAxis:UILayoutConstraintAxisHorizontal];
[self.rightLabel mas_makeConstraints:^(MASConstraintMaker * make) {
make.top.left.right.equalTo(self.rightView).mas_offset(UIEdgeInsetsMake(20, 20, 0, 20)).priorityMedium();
}];
}
// 3
[self.leftView mas_remakeConstraints:^(MASConstraintMaker * make) {
make.top.left.right.equalTo(self.view).mas_offset(UIEdgeInsetsMake(30, 30, 0, 30)).priorityMedium();
}];
[self.rightView mas_remakeConstraints:^(MASConstraintMaker * make) {
make.left.bottom.right.equalTo(self.view).mas_offset(UIEdgeInsetsMake(0, 30, 30, 30)).priorityMedium();
make.top.equalTo(self.leftView.mas_bottom).offset(30).priorityMedium();
make.height.equalTo(self.leftView.mas_height).priorityLow();
}];
}
// 两个视图水平排列
- (void) horizontalTwoViews {
if (self.leftView == nil) {
self.leftView = [[UIView alloc] initWithFrame:CGRectZero];
self.leftView.backgroundColor = [UIColor redColor];
[self.view addSubview:self.leftView];
}
if (self.rightView == nil) {
self.rightView = [[UIView alloc] initWithFrame:CGRectZero];
self.rightView.backgroundColor = [UIColor blueColor];
[self.view addSubview:self.rightView];
}
[self.leftView mas_remakeConstraints:^(MASConstraintMaker * make) {
make.top.left.bottom.equalTo(self.view).mas_offset(UIEdgeInsetsMake(30, 30, 30, 0)).priorityMedium();
}];
[self.rightView mas_remakeConstraints:^(MASConstraintMaker * make) {
make.top.bottom.right.equalTo(self.view).mas_offset(UIEdgeInsetsMake(30, 0, 30, 30)).priorityMedium();
make.left.equalTo(self.leftView.mas_right).mas_offset(@30).priorityMedium();
make.width.equalTo(self.leftView.mas_width).priorityLow();
}];
}
标号的注释解释
- 该方法在旋转发生的时候调用，方法内调用不同的布局方案。这里选用的是 - (void) viewDidLayoutSubviews 方法，而不是 - (void) viewWillTransitionToSize:(CGSize)size withTransitionCoordinator:(id<UIViewControllerTransitionCoordinator>)coordinator 方法。因为后者是will，是在旋转发生之前调用，感觉上并不直观。还有一种选择是使用通知。但是通知的相应方法会被多次（3次）调用的现象，所以这里也没有选择使用。
- label具有压缩阻力，会根据内容的多少来决定自身的尺寸。把它的压缩优先级设为1，用以保证它与父视图的约束关系。
- Masonry主要有三个方法来创建约束，分别为 mas_makeConstraints、mas_remakeConstraints、和mas_updateConstraints。第一个会直接创建约束，第二个会删除之前的约束再重新创建约束，第三个是不删除之前的约束添加新约束。
