1、使用代碼創建AutoLayout 必須先禁用autoresizing

/**
 *  某個控件在父控件中居中
 */
- (void)centerTest
{
    // 1.添加控件
    UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    [self.view addSubview:blueView];
    
    // 2.添加約束
    // 關閉autoresizing
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    
    /**
     寬高:100
     位置:在父控件中居中
     */
    // blueView的width == 100
    NSLayoutConstraint *width = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:100];
    [blueView addConstraint:width];
    
    // blueView的height == 100
    NSLayoutConstraint *height = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:100];
    [blueView addConstraint:height];
    
    // blueView的CenterX == self.view的CenterX * 1.0 + 0.0
    NSLayoutConstraint *centerX = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0.0];
    [self.view addConstraint:centerX];
    
    // blueView的CenterY == self.view的CenterY * 1.0 + 0.0
    NSLayoutConstraint *centerY = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0.0];
    [self.view addConstraint:centerY];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    // 1.添加控件
    UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:blueView];
    
    UIView *redView = [[UIView alloc] init];
    redView.backgroundColor = [UIColor redColor];
    redView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:redView];
    
    // 2.約束藍色
    // 2.1.高度
    NSLayoutConstraint *blueHeight = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeNotAnAttribute multiplier:1.0 constant:40];
    [blueView addConstraint:blueHeight];
    // 2.2.左邊間距
    CGFloat margin = 20;
    NSLayoutConstraint *blueLeft = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeLeft relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeft multiplier:1.0 constant:margin];
    [self.view addConstraint:blueLeft];
    // 2.3.頂部間距
    NSLayoutConstraint *blueTop = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTop multiplier:1.0 constant:margin];
    [self.view addConstraint:blueTop];
    // 2.4.右邊間距
    NSLayoutConstraint *blueRight = [NSLayoutConstraint constraintWithItem:blueView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeRight multiplier:1.0 constant:-margin];
    [self.view addConstraint:blueRight];
    
    // 3.約束紅色
    // 3.1.讓紅色右邊 == 藍色右邊
    NSLayoutConstraint *redRight = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeRight relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeRight multiplier:1.0 constant:0.0];
    [self.view addConstraint:redRight];

    // 3.2.讓紅色高度 == 藍色高度
    NSLayoutConstraint *redHeight = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeHeight multiplier:1.0 constant:0.0];
    [self.view addConstraint:redHeight];
    
    // 3.3.讓紅色頂部 == 藍色底部 + 間距
    NSLayoutConstraint *redTop = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeBottom multiplier:1.0 constant:margin];
    [self.view addConstraint:redTop];
    
    // 3.4.讓紅色寬度 == 藍色寬度 * 0.5
    NSLayoutConstraint *redWidth = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeWidth multiplier:0.5 constant:0.0];
    [self.view addConstraint:redWidth];
}

2、使用VFL語言創建AutoLayout中的約束
示例1的效果和代碼如下:

// 頂部一個blueView 下面一個redView,其中redView的左邊和blueView的中心對齊
- (void)VFLtest1
{
    // 1.添加控件
    UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:blueView];
    
    UIView *redView = [[UIView alloc] init];
    redView.backgroundColor = [UIColor redColor];
    redView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:redView];
    
    // 2.VFL生成約束,注意,對象必須用[]括起來
    NSArray *conts = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-20-[blueView]-20-|" options:0 metrics:nil views:@{@"blueView" : blueView}];
    [self.view addConstraints:conts];
    
    NSArray *conts2 = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-20-[blueView(40)]-20-[redView(==blueView)]" options:NSLayoutFormatAlignAllRight metrics:nil views:@{@"blueView" : blueView, @"redView" : redView}];
    [self.view addConstraints:conts2];
    
    // 3.注意,VFL暫時不支持 a = b*0.5這樣的語法
    NSLayoutConstraint *redWidth = [NSLayoutConstraint constraintWithItem:redView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:blueView attribute:NSLayoutAttributeWidth multiplier:0.5 constant:0.0];
    [self.view addConstraint:redWidth];
}

示例2的效果和代碼 如下:

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    // 1.添加控件
    UIView *blueView = [[UIView alloc] init];
    blueView.backgroundColor = [UIColor blueColor];
    blueView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:blueView];
    
    UIView *redView = [[UIView alloc] init];
    redView.backgroundColor = [UIColor redColor];
    redView.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:redView];
    
    // 2.VFL生成約束,注意使用下面的宏,必須保證鍵值對的名稱一樣
    NSDictionary *mertrics = @{@"margin" : @20}; // 參數\數值
    NSDictionary *views = NSDictionaryOfVariableBindings(blueView, redView);
    NSArray *conts = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-margin-[blueView]-margin-[redView(==blueView)]-margin-|" options:NSLayoutFormatAlignAllTop | NSLayoutFormatAlignAllBottom metrics:mertrics views:views];
    
    NSArray *conts2 = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[blueView(==blueHeight)]-margin-|" options:0 metrics:@{@"blueHeight" : @40, @"margin" : @20} views:views];
    [self.view addConstraints:conts];
    [self.view addConstraints:conts2];
}

3、使用AutoLayout中的約束創建動畫
將storyboard中的約束 拖到.m文件中,使之成為IBOutlet對象,例如:

@property (weak, nonatomic) IBOutlet NSLayoutConstraint *leftMarginConstraint;

@property (weak, nonatomic) IBOutlet NSLayoutConstraint *widthConstraint;

當事件觸發時,改變其constant值,然後調用約束所在的對象的 layoutIfNeeded方法,固定的~ 例如:

self.leftMarginConstraint.constant = 100;

self.widthConstraint.constant = 200;

 

[UIView animateWithDuration:2.0 animations:^{

[self.view layoutIfNeeded];

[self.redView layoutIfNeeded];

}];

4、建議上邊距 使用Top Layout Guide,即狀態欄下邊線,因為iOS6是以狀態欄下邊線為原點,而iOS7以上是以屏幕的左上角為原點