NSLayoutConstraint

屏幕兼容的问题

为了让我们的应用在不容尺寸的屏幕下都能 “正常”的表示，我们尽量不要把数据写死。

大多数可视元素都是一个矩形区域，当然这个矩形区域有坐标的，我们有了这个区域坐标就能确定可视元素的现实位置了。

但是iphone5 和以前的屏幕不一样了，在以前的设备中，我们可以添加一个 [email protected] 来适应retina屏幕，但是iphoen5咋办呢？

ios 引入了 Auto Layout 的东东，这个要和UIViewAutoresizing 区分下。

看下面代码

- (void)viewDidLoad
{
[super viewDidLoad];

UIView *aView = [[UIView alloc] init];
aView.backgroundColor = [UIColor redColor];

//为了不和autosizing冲突，我们设置No

[aView setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.view addSubview:aView];

UIView *bView = [[UIView alloc] init];
bView.backgroundColor = [UIColor blueColor];
[bView setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.view addSubview:bView];

NSDictionary *views = NSDictionaryOfVariableBindings(aView, bView);

//NSDictionaryOfVariableBindings 宏 其实 NSDictionaryOfVariableBindings(v1, v2, v3) 等效于 [NSDictionary dictionaryWithObjectsAndKeys:v1, @"v1", v2, @"v2", v3, @"v3", nil];
[self.view addConstraints:
[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-(>=50)-[aView(100)]"
options:0
metrics:nil
views:views]];

[self.view addConstraints:
[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-(>=100)-[aView(50)]"
options:0
metrics:nil
views:views]];

[self.view addConstraints:
[NSLayoutConstraint constraintsWithVisualFormat:@"H:[bView(==aView)]"
options:0
metrics:nil
views:views]];
[self.view addConstraints:
[NSLayoutConstraint constraintsWithVisualFormat:@"V:[bView(==aView)]"
options:0
metrics:nil
views:views]];

[self.view addConstraint:
[NSLayoutConstraint constraintWithItem:bView
attribute:NSLayoutAttributeLeft
relatedBy:NSLayoutRelationEqual
toItem:aView
attribute:NSLayoutAttributeRight
multiplier:1
constant:10]];
//添加一个限制 等效于 bView.frame.origin.x = (aView.frame.origin.x +aView.frame.size.width) * 1 + 10,好像是这样的！个人觉得！

它是一种依赖关系，bView依赖aView，这样就算aView变了，bView也会跟着变换。
[self.view addConstraint:
[NSLayoutConstraint constraintWithItem:bView
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:aView
attribute:NSLayoutAttributeTop
multiplier:1
constant:0]];

[aView release];
[bView release];
}

constraintWithItem:attribute:relatedBy:toItem:attribute:multiplier:constant:

Create a constraint of the form "view1.attr1 <relation> view2.attr2 * multiplier + constant".

属性

typedef NS_ENUM(NSInteger, NSLayoutAttribute) {
NSLayoutAttributeLeft = 1,
NSLayoutAttributeRight,
NSLayoutAttributeTop,
NSLayoutAttributeBottom,
NSLayoutAttributeLeading,
NSLayoutAttributeTrailing,
NSLayoutAttributeWidth,
NSLayoutAttributeHeight,
NSLayoutAttributeCenterX,
NSLayoutAttributeCenterY,
NSLayoutAttributeBaseline,

NSLayoutAttributeNotAnAttribute = 0
};

关系

typedef NS_ENUM(NSInteger, NSLayoutRelation) {
NSLayoutRelationLessThanOrEqual = -1,
NSLayoutRelationEqual = 0,
NSLayoutRelationGreaterThanOrEqual = 1,
};

最后的结果就是 “view1.attr1 < >= 或者 == 或者 <= > view2.attr2 * multiplier + constant”