代码实现 autolayout功能（约束）-学习记录一

因为我们的工程都是用代码画UI，除非重构才有可能用IB或者storyboard来实现autolayout，因此学习一下用代码实现约束

UIImageView *logoImage = [[UIImageView alloc] initWithFrame:CGRectZero];

logoImage.image = [UIImage imageNamed:@"al_loginLogo.png"];

//将自适应向布局约束的转化关掉(根据情况有时需要有时不需要)  

[logoImage setTranslatesAutoresizingMaskIntoConstraints:NO];

    NSMutableArray *constraints = [NSMutableArray array];

    //horizontal

//水平方向离父视图70，logoImage宽为100

    id constraintObjectH = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-70-[logoImage(==100)]" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(logoImage)];

    [constraints addObjectsFromArray:constraintObjectH];

    //vertical

//垂直方向离父视图32，logoImage高为60

    id constraintObjectV = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-32-[logoImage(==60)]" options:NSLayoutFormatDirectionLeadingToTrailing metrics:nil views:NSDictionaryOfVariableBindings(logoImage)];

    [constraints addObjectsFromArray:constraintObjectV];

    [self.view addConstraints:constraints];