以编程方式将视图的前沿与约束对齐

Question

I am having an UIImageView (say imageView1 ) and a UITextView (say textView1 ) which have to be displayed vertically (one [ imageView1 ] below the other [ textView1 ]) beginning with the same margin position as of textView1 . I have to achieve this through autolayout programmatically.

I know that this can be done by setting the vertical constraints like below for both the views.

NSLayoutConstraint constraintsWithVisualFormat:@"V:|[textView1]"

But the problem I have here is I already have many text views( textView2 , textView3 ) arranged in horizontal before and after this textView1 .

I have already added many autolayout constraints to this textView1 through storyboard. Based on the different screen size and orientation the textView1 margin differs as per the constraints that are provided on the storyboard for this.

Now how can I provide the autolayout constraint programmatically in such a way that my imageView1 is to align in par vertically with the same margin as that of textView1 ?

ps: imageView1 is created programmatically in code but where as all other views that I mentioned above are created through storyboard.

+ Adding images for easy understanding

In the image, imageView1 is the UI Image. I have created it in storyboard just for understanding purpose but in real it will be created programmatically and this have to be aligned to the margin of UITextView ( textView1 ) present below it.

This is the constraint that I want to create it through programmatically(In case this is the real question here :).

This constraint is to always make sure that imageView1 and textView1 start originating from the same margin.

How to define this constraint programmatically ?

Answer 1

Rather than using the visual format, you can just instantiate a constraint directly, eg

[NSLayoutConstraint
    constraintWithItem:imageView1 attribute:NSLayoutAttributeLeading
    relatedBy:NSLayoutRelationEqual
    toItem:textView1 attribute:NSLayoutAttributeLeading
    multiplier:1.0 constant:0.0]

Answer 2

使用Masonry以编程方式设置约束。它非常易于使用，并为用户减少了很多复杂性。

 https://github.com/SnapKit/Masonry

Answer 3

...您可以尝试构建一个UIView ，设置所需的约束，并将其用作UIImageView的占位符（ 稍后您可以将其添加到此类视图中 ），或者在另一侧使用UICollectionView 。

Answer 4

You can set the options argument in constraintsWithVisualFormat:options:metrics:views: check Apple Class Reference .

Your code might be as follows

NSString* leadingConstraintsExpression = @"V:[imageView1][textView1]";

NSDictionary* viewsDictionary = NSDictionaryOfVariableBindings(imageView1,textView1);

NSArray* leadingConstraints = [NSLayoutConstraint 
                                  constraintsWithVisualFormat:leadingConstraintsExpression
                                                      options:NSLayoutFormatAlignAllLeading 
                                                      metrics:nil 
                                                        views:viewsDictionary];

[self.view addConstraints:leadingConstraints];