如何为UIImageView设置乘数

Question

我有一个图像的宽度= 189，高度= 41，所以我为这个UIImageView定义了2个约束，如下所示:

NSArray *constraint_V=[NSLayoutConstraint constraintsWithVisualFormat:@"V:[Title(41)]" options:0 metrics:nil views:viewsDictionary];
[imgVwLogo addConstraints:constraint_V];
NSArray *constraint_H=[NSLayoutConstraint constraintsWithVisualFormat:@"H:[Title(189)]" options:0 metrics:nil views:viewsDictionary];
[imgVwLogo addConstraints:constraint_H];

它在iPhone 4s上看起来不错，但当涉及到iPhone 6 plus时，我觉得UIImageview的高度应该增加一点，因为图像看起来垂直缩小了。也许加一个乘数可以解决这个问题。但是我不知道如何为我的元素选择乘数因子。设置为height/width

NSLayoutConstraint *imgtitlecon_Aspect_Ratio =[NSLayoutConstraint
                                          constraintWithItem:imgVwLogo
                                          attribute:NSLayoutAttributeHeight
                                          relatedBy:NSLayoutRelationEqual
                                          toItem:imgVwLogo
                                          attribute:NSLayoutAttributeHeight
                                          multiplier:41/189
                                          constant:0.0f];
[imgVwLogo addConstraint:imgtitlecon_Aspect_Ratio];

但是这使得UIImageView在4s上完全消失。我该如何解决这个问题?

更新

  //------------------------ Title image --------------------------------------------
 NSArray *constraint_V=[NSLayoutConstraint constraintsWithVisualFormat:@"V:   [Title(41)]" options:0 metrics:nil views:viewsDictionary];
[imgVwLogo addConstraints:constraint_V];
NSArray *constraint_H=[NSLayoutConstraint constraintsWithVisualFormat:@"H:[Title(189)]" options:0 metrics:nil views:viewsDictionary];
[imgVwLogo addConstraints:constraint_H];

// Center Horizontally
NSLayoutConstraint *centerXConstraintimgTitle =
[NSLayoutConstraint constraintWithItem:imgVwLogo
                             attribute:NSLayoutAttributeCenterX
                             relatedBy:NSLayoutRelationEqual
                                toItem:self.view
                             attribute:NSLayoutAttributeCenterX
                            multiplier:1.0
                              constant:0.0];
[self.view addConstraint:centerXConstraintimgTitle];

NSLayoutConstraint *imgtitlecon_Aspect_Ratio =[NSLayoutConstraint
                                          constraintWithItem:imgVwLogo
                                          attribute:NSLayoutAttributeHeight
                                          relatedBy:NSLayoutRelationEqual
                                          toItem:imgVwLogo
                                          attribute:NSLayoutAttributeHeight
                                          multiplier:(41.0f/189.0f)
                                          constant:0.0f];
[imgVwLogo addConstraint:imgtitlecon_Aspect_Ratio];


NSArray *Titleconstraint_POS_H=[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-titleVspace-[Title]-titleVspace-|" options:0 metrics:metrics views:viewsDictionary];
[self.view addConstraints:Titleconstraint_POS_H];

//------------------------ Title image ------------------------------------------------------------

最后对齐所有元素

NSArray *btncon_POS_V=[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-50-[Title]-0-[vwgap]-0-[lblFirst]-0-[lblSecond]-20-[textusername]-10-[txtpassword]-20-[btnLogin]-0-[vwgapCopy]-0-[copyrightlbl]" options:0 metrics:nil views:viewsDictionary];
[self.view addConstraints:btncon_POS_V];

Answer 1

如果你只想从代码中设置宽高比，那么你只需要改变代码中的一些小东西。

[imgVwLogo addConstraint:[NSLayoutConstraint
                                      constraintWithItem:imgVwLogo
                                      attribute:NSLayoutAttributeHeight
                                      relatedBy:NSLayoutRelationEqual
                                      toItem:imgVwLogo
                                      attribute:NSLayoutAttributeWidth
                                      multiplier:(41.0f/189.0f)
                                      constant:0.0f]];

编辑1:根据问题编辑答案如下代码。编辑2:请将568.0f的值改为self的值。在storyboard中设计时的视图高度

[imgVwLogo addConstraint:[NSLayoutConstraint
                                      constraintWithItem:imgVwLogo
                                      attribute:NSLayoutAttributeHeight
                                      relatedBy:NSLayoutRelationEqual
                                      toItem:imgVwLogo
                                      attribute:NSLayoutAttributeWidth
                                      multiplier:(41.0f/189.0f)
                                      constant:0.0f]];
[self.view addConstraint:[NSLayoutConstraint
                                      constraintWithItem:imgVwLogo
                                      attribute:NSLayoutAttributeWidth
                                      relatedBy:NSLayoutRelationEqual
                                      toItem:self.view
                                      attribute:NSLayoutAttributeHeight
                                      multiplier:(189.0f/568.0f)
                                      constant:0.0f]];
[self.view addConstraint:[NSLayoutConstraint
                                      constraintWithItem:imgVwLogo
                                      attribute:NSLayoutAttributeCenterX
                                      relatedBy:NSLayoutRelationEqual
                                      toItem:self.view
                                      attribute:NSLayoutAttributeCenterX
                                      multiplier:1.0f
                                      constant:0.0f]];
[self.view addConstraint:[NSLayoutConstraint
                                      constraintWithItem:imgVwLogo
                                      attribute:NSLayoutAttributeTop
                                      relatedBy:NSLayoutRelationEqual
                                      toItem:self.view
                                      attribute:NSLayoutAttributeTop
                                      multiplier:1.0f
                                      constant:50.0f]];