如何为 UIImageView 设置乘数

Question

我有一个图像，其宽度 = 189，高度 = 41，所以我为此 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];

在iPhone4s上看起来不错，但是到了iPhone6plus我觉得UIImageview的高度应该增加一点，因为图像看起来缩小了垂直。也许添加乘数可能是解决方案。但是我不知道如何 select 我的元素的乘数。我设置为 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];

但这使得 UIImageView 即使在 4s 上也完全消失了。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 ------------------------------------------------------------

最后我对齐所有元素

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

如果您只想从代码中设置宽高比，那么您只需要在代码中做一些小改动。开始了。

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

编辑 1：根据问题编辑答案将如下代码所示。编辑 2：请在故事板设计时将 568.0f 值更改为 self.view 高度的值。

[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]];

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