NSLayoutConstraint

屏幕兼容的問題

為了讓我們的應用在不容尺寸的屏幕下都能 “正常”的表示，我們盡量不要把數據寫死。

大多數可視元素都是一個矩形區域，當然這個矩形區域有坐標的，我們有了這個區域坐標就能確定可視元素的現實位置了。

但是iphone5 和以前的屏幕不一樣了，在以前的設備中，我們可以添加一個 [e-mail] 來適應retina屏幕，但是iphoen5咋辦呢？

ios 引入了 Auto Layout 的東東，這個要和UIViewAutoresizing 區分下。

看下面代碼

- (void)viewDidLoad
{
    [super viewDidLoad];
        
    UIView *aView = [[UIView alloc] init];
    aView.backgroundColor = [UIColor redColor];

//為了不和autosizing沖突，我們設置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  其實 NSDictionaryOfVariableBindings(v1, v2, v3) 等效於 [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]];
    //添加一個限制  等效於 bView.frame.origin.x  = (aView.frame.origin.x +aView.frame.size.width)  * 1  + 10,好像是這樣的！個人覺得！

  它是一種依賴關系，bView依賴aView，這樣就算aView變了，bView也會跟着變換。
    [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".

屬性

typedef NS_ENUM(NSInteger, NSLayoutAttribute) {
    NSLayoutAttributeLeft = 1,
    NSLayoutAttributeRight,
    NSLayoutAttributeTop,
    NSLayoutAttributeBottom,
    NSLayoutAttributeLeading,
    NSLayoutAttributeTrailing,
    NSLayoutAttributeWidth,
    NSLayoutAttributeHeight,
    NSLayoutAttributeCenterX,
    NSLayoutAttributeCenterY,
    NSLayoutAttributeBaseline,
    
    NSLayoutAttributeNotAnAttribute = 0
};

關系

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

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