ios NSLayoutConstraint
为了让我们的应用在不同尺寸的屏幕下都能 “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 xx.@2x.png来适应retina屏幕，但是iphoen5咋办呢？ios6引入了 Auto Layout的东东，这个要和UIViewAutoresizing区分下。
1.看下面代码:
-(void)viewDidLoad
{
[superviewDidLoad];
UIView *aView =[[UIView alloc] init];
aView.backgroundColor = [UIColor redColor];
//为了不和autosizing冲突，我们设置No
[aView setTranslatesAutoresizingMaskIntoConstraints:NO];//不把AutoresizingMask转化为Constraints
[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);
/* This macro is a helper for making view dictionariesfor +constraintsWithVisualFormat:options:metrics:views:.
NSDictionaryOfVariableBindings(v1, v2, v3) isequivalent（等效于） to [NSDictionarydictionaryWithObjectsAndKeys:v1, @"v1", v2, @"v2", v3,@"v3", nil];
*/
[self.viewaddConstraints:
[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.viewaddConstraints:
[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.viewaddConstraint:
[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！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.viewaddConstraint:
[NSLayoutConstraint constraintWithItem:bView
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:aView
attribute:NSLayoutAttributeTop
multiplier:1
constant:0]];
[aView release];
[bView release];
}
2.constraintWithItem:attribute:relatedBy:toItem:attribute:multiplier:constant:
/* Create constraints explicitly. Constraints are of the form "view1.attr1 = view2.attr2 * multiplier + constant"
If your equation does not have a second view and attribute, use nil and NSLayoutAttributeNotAnAttribute.
*/
3.属性
typedefNS_ENUM(NSInteger, NSLayoutAttribute) {
NSLayoutAttributeLeft = 1,
NSLayoutAttributeRight,
NSLayoutAttributeTop,
NSLayoutAttributeBottom,
NSLayoutAttributeLeading,
NSLayoutAttributeTrailing,
NSLayoutAttributeWidth,
NSLayoutAttributeHeight,
NSLayoutAttributeCenterX,
NSLayoutAttributeCenterY,
NSLayoutAttributeBaseline,
NSLayoutAttributeNotAnAttribute = 0
};
4.关系
typedefNS_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”
5.Visual Format Language (视觉形式语言)
