ios之快速领会VFL的demo

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。

http://www.thinkandbuild.it/learn-to-love-auto-layout-programmatically/

https://github.com/ariok/TB_ProgrammaticallyAutoLayout  代码demo

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:
                                                                    metrics:nil
                                                                      views:viewsDictionary];

    NSArray *constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[redView(100)]"
                                                                    options:
                                                                    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:
                                                                        metrics:nil
                                                                          views:viewsDictionary];

    NSArray *constraint_POS_H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-20-[redView]"
                                                                        options:
                                                                        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:
                                                                        metrics:nil
                                                                          views:viewsDictionary];
    NSArray *red_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[redView(100)]"
                                                                        options:
                                                                        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:
                                                                           metrics:nil
                                                                             views:viewsDictionary];

    NSArray *yellow_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[yellowView(100)]"
                                                                           options:
                                                                           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:
                                                                        metrics:nil
                                                                          views:viewsDictionary];

    NSArray *constraint_POS_H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-20-[redView]-10-[yellowView]"
                                                                        options:
                                                                        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:
                                                                        metrics:nil
                                                                          views:viewsDictionary];

    NSArray *red_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[redView(100)]"
                                                                        options:
                                                                        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:
                                                                           metrics:nil
                                                                             views:viewsDictionary];

    NSArray *yellow_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[yellowView(100)]"
                                                                           options:
                                                                           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:
                                                                        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": @,
                              @"redHeight": @,
                              @"yellowWidth": @,
                              @"yellowHeight": @,
                              @"topMargin": @,
                              @"leftMargin": @,
                              @"viewSpacing":@
                              };

    // 2. Define the views Sizes
    NSArray *red_constraint_H = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[redView(redHeight)]"
                                                                        options:
                                                                        metrics:metrics
                                                                          views:viewsDictionary];

    NSArray *red_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[redView(redWidth)]"
                                                                        options:
                                                                        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:
                                                                           metrics:metrics
                                                                             views:viewsDictionary];

    NSArray *yellow_constraint_V = [NSLayoutConstraint constraintsWithVisualFormat:@"H:[yellowView(yellowWidth)]"
                                                                           options:
                                                                           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:
                                                                        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":@, @"hSpacing":@};

    // 2. Define the view Position and automatically the Size
    NSArray *constraint_POS_V = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-vSpacing-[redView]-vSpacing-|"
                                                                        options:
                                                                        metrics:metrics
                                                                          views:viewsDictionary];

    NSArray *constraint_POS_H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-hSpacing-[redView]-hSpacing-|"
                                                                      options:
                                                                      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":@, @"hSpacing":@};

    // 2. Define the view Position and automatically the Size (for the redView)
    NSArray *constraint_POS_V = [NSLayoutConstraint constraintsWithVisualFormat:@"V:|-vSpacing-[redView]-vSpacing-|"
                                                                        options:
                                                                        metrics:metrics
                                                                          views:viewsDictionary];

    NSArray *constraint_POS_H = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-hSpacing-[redView]-hSpacing-|"
                                                                        options:
                                                                        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]];

}