在网上看到一篇blog，超正！快速领会ios的vfl。 这里贴上blog的地址。
https://github.com/ariok/TB_ProgrammaticallyAutoLayout 代码demo
demo代码如下：
demo代码如下：
/* Initial views setup */
- (void)setupViews
{
self.redView = [UIView new];
self.redView.translatesAutoresizingMaskIntoConstraints = NO;
self.redView.backgroundColor = [UIColor colorWithRed:0.95 green:0.47 blue:0.48 alpha:1.0];
self.yellowView = [UIView new];
self.yellowView.translatesAutoresizingMaskIntoConstraints = NO;
self.yellowView.backgroundColor = [UIColor colorWithRed:1.00 green:0.83 blue:0.58 alpha:1.0];
[self.view addSubview:self.redView];
[self.view addSubview:self.yellowView];
}
/*
Hey Devs... the code in the next functions has to be intended for tutorial purposes only.
I have created work-alone examples that contain a lot of code duplication... not a good practice but way easier to explain :P
*/
/* EXAMPLE 1 */
- (void)example_1
{
// 1. Create a dictionary of views
NSDictionary *viewsDictionary = @{@"redView":self.redView};
// 2. Define the redView Size
NSArray *constraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[redView(100)]"
options:0
metrics:nil
views:viewsDictionary];
NSArray *constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[redView(100)]"
options:0
metrics:nil
views:viewsDictionary];
[self.redView addConstraints:constraint_H];
[self.redView addConstraints:constraint_V];
// 3. Define the redView Position
NSArray *constraint_POS_V = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-30-[redView]"
options:0
metrics:nil
views:viewsDictionary];
NSArray *constraint_POS_H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-20-[redView]"
options:0
metrics:nil
views:viewsDictionary];
// 3.B ...and try to change the visual format string
//NSArray *constraint_POS_V = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[redView]-30-|" options:0 metrics:nil views:viewsDictionary];
//NSArray *constraint_POS_H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[redView]" options:0 metrics:nil views:viewsDictionary];
[self.view addConstraints:constraint_POS_H];
[self.view addConstraints:constraint_POS_V];
}
/* EXAMPLE 2 */
- (void)example_2
{
// 1. Create a dictionary of views
NSDictionary *viewsDictionary = @{@"redView":self.redView, @"yellowView":self.yellowView};
// 2. Define the views Sizes
NSArray *red_constraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[redView(100)]"
options:0
metrics:nil
views:viewsDictionary];
NSArray *red_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[redView(100)]"
options:0
metrics:nil
views:viewsDictionary];
[self.redView addConstraints:red_constraint_H];
[self.redView addConstraints:red_constraint_V];
NSArray *yellow_constraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[yellowView(200)]"
options:0
metrics:nil
views:viewsDictionary];
NSArray *yellow_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[yellowView(100)]"
options:0
metrics:nil
views:viewsDictionary];
[self.yellowView addConstraints:yellow_constraint_H];
[self.yellowView addConstraints:yellow_constraint_V];
// 3. Define the views Positions
NSArray *constraint_POS_V = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-30-[redView]-40-[yellowView]"
options:0
metrics:nil
views:viewsDictionary];
NSArray *constraint_POS_H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-20-[redView]-10-[yellowView]"
options:0
metrics:nil
views:viewsDictionary];
[self.view addConstraints:constraint_POS_V];
[self.view addConstraints:constraint_POS_H];
}
/* EXAMPLE 3 */
- (void)example_3
{
// 1. Create a dictionary of views
NSDictionary *viewsDictionary = @{@"redView":self.redView, @"yellowView":self.yellowView};
// 2. Define the views Sizes
NSArray *red_constraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[redView(100)]"
options:0
metrics:nil
views:viewsDictionary];
NSArray *red_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[redView(100)]"
options:0
metrics:nil
views:viewsDictionary];
[self.redView addConstraints:red_constraint_H];
[self.redView addConstraints:red_constraint_V];
NSArray *yellow_constraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[yellowView(150)]"
options:0
metrics:nil
views:viewsDictionary];
NSArray *yellow_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[yellowView(100)]"
options:0
metrics:nil
views:viewsDictionary];
[self.yellowView addConstraints:yellow_constraint_H];
[self.yellowView addConstraints:yellow_constraint_V];
// 3. Define the views Positions using options
NSArray *constraint_POS_V = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-120-[redView]"
options:0
metrics:nil
views:viewsDictionary];
NSArray *constraint_POS = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-20-[redView]-10-[yellowView]"
options:NSLayoutFormatAlignAllTop
metrics:nil views:viewsDictionary];
[self.view addConstraints:constraint_POS_V];
[self.view addConstraints:constraint_POS];
}
/* EXAMPLE 4 */
- (void)example_4
{
// 1. Create a dictionary of views and metrics
NSDictionary *viewsDictionary = @{@"redView":self.redView, @"yellowView":self.yellowView};
NSDictionary *metrics = @{@"redWidth": @100,
@"redHeight": @100,
@"yellowWidth": @100,
@"yellowHeight": @150,
@"topMargin": @120,
@"leftMargin": @20,
@"viewSpacing":@10
};
// 2. Define the views Sizes
NSArray *red_constraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[redView(redHeight)]"
options:0
metrics:metrics
views:viewsDictionary];
NSArray *red_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[redView(redWidth)]"
options:0
metrics:metrics
views:viewsDictionary];
[self.redView addConstraints:red_constraint_H];
[self.redView addConstraints:red_constraint_V];
NSArray *yellow_constraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[yellowView(yellowHeight)]"
options:0
metrics:metrics
views:viewsDictionary];
NSArray *yellow_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[yellowView(yellowWidth)]"
options:0
metrics:metrics
views:viewsDictionary];
[self.yellowView addConstraints:yellow_constraint_H];
[self.yellowView addConstraints:yellow_constraint_V];
// 3. Define the views Positions
NSArray *constraint_POS_V = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-topMargin-[redView]"
options:0
metrics:metrics
views:viewsDictionary];
NSArray *constraint_POS = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-leftMargin-[redView]-viewSpacing-[yellowView]"
options:NSLayoutFormatAlignAllTop
metrics:metrics
views:viewsDictionary];
[self.view addConstraints:constraint_POS_V];
[self.view addConstraints:constraint_POS];
}
/* EXAMPLE 5 */
- (void)example_5
{
// 1. Create a dictionary of views and metrics
NSDictionary *viewsDictionary = @{@"redView":self.redView};
NSDictionary *metrics = @{@"vSpacing":@30, @"hSpacing":@10};
// 2. Define the view Position and automatically the Size
NSArray *constraint_POS_V = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-vSpacing-[redView]-vSpacing-|"
options:0
metrics:metrics
views:viewsDictionary];
NSArray *constraint_POS_H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-hSpacing-[redView]-hSpacing-|"
options:0
metrics:metrics
views:viewsDictionary];
[self.view addConstraints:constraint_POS_V];
[self.view addConstraints:constraint_POS_H];
}
/* EXAMPLE 6 */
- (void)example_6
{
// 1. Create a dictionary of views
NSDictionary *viewsDictionary = @{@"redView": self.redView, @"yellowView": self.yellowView};
NSDictionary *metrics = @{@"vSpacing":@30, @"hSpacing":@10};
// 2. Define the view Position and automatically the Size (for the redView)
NSArray *constraint_POS_V = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-vSpacing-[redView]-vSpacing-|"
options:0
metrics:metrics
views:viewsDictionary];
NSArray *constraint_POS_H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-hSpacing-[redView]-hSpacing-|"
options:0
metrics:metrics
views:viewsDictionary];
[self.view addConstraints:constraint_POS_V];
[self.view addConstraints:constraint_POS_H];
// 3. Define sizes thanks to relations with another view (yellowView in relation with redView)
[self.view addConstraint:[NSLayoutConstraint
constraintWithItem:self.yellowView
attribute:NSLayoutAttributeWidth
relatedBy:NSLayoutRelationEqual
toItem:self.redView
attribute:NSLayoutAttributeWidth
multiplier:0.5
constant:0.0]];
[self.view addConstraint:[NSLayoutConstraint
constraintWithItem:self.yellowView
attribute:NSLayoutAttributeHeight
relatedBy:NSLayoutRelationEqual
toItem:self.redView
attribute:NSLayoutAttributeHeight
multiplier:0.5
constant:0.0]];
// 4. Define position thanks to relations with another view (yellowView in relation with redView)
[self.view addConstraint:[NSLayoutConstraint
constraintWithItem:self.yellowView
attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationEqual
toItem:self.redView
attribute:NSLayoutAttributeCenterX
multiplier:1.0
constant:0.0]];
[self.view addConstraint:[NSLayoutConstraint
constraintWithItem:self.yellowView
attribute:NSLayoutAttributeCenterY
relatedBy:NSLayoutRelationEqual
toItem:self.redView
attribute:NSLayoutAttributeCenterY
multiplier:1.0
constant:0.0]];
}