Question

我有几个部分透明的PNG叠加层，可以在视图中相互叠加显示。叠加的数量取决于运行时条件。我想在Swift中创建UIImageView个实例并将它们添加到视图中。

在故事板中添加UIImageView并通过Swift设置图像时，我没有遇到任何问题。在这种情况下，我将UIImageView的前导，尾随，顶部和底部固定到父包装UIView的前导，尾随，顶部和底部。在UIImageView的属性检查器中，我将“内容模式”设置为“Aspect Fit”，当Swift设置图像时，大图像会很好地缩小。用户可以在iPhone小屏幕上看到整个图像。

当我动态创建UIImageView并将其添加到同一父包装器UIView时，我遇到了约束问题。有太多的限制要满足。

我无法弄清楚为什么通过Swift创建的UIImageView与通过故事板创建的UIImageView不同。

如何通过Swift创建的UIImageView行为与通过故事板创建的UIImageView一样？

Swift代码，用于设置通过故事板创建的UIImageView上的图像以及通过Swift创建的UIImageView。

override func viewDidLoad() -> Void {
    super.viewDidLoad();

    let imageFilePath: String = Bundle.main.resourceURL!.appendingPathComponent("img/a.png", isDirectory: false).path;

    // Use the outlet to set the image in the UIImageView created in the storyboard.
    // This works.

    self.storyboardImageView.image = UIImage(contentsOfFile: imageFilePath);

    // Create a UIImageView programatically and add it to the same wrapper UIView
    // that also contains the UIImageView above.
    // This doesn't work.

    let swiftImageView: UIImageView = UIImageView(image: UIImage(contentsOfFile: imageFilePath));

    // The presence of the following line makes no difference
    //
    swiftImageView.contentMode = .scaleAspectFill;

    self.storyboardWrapperView.addSubview(swiftImageView);

    swiftImageView.topAnchor.constraint(equalTo: self.storyboardWrapperView.topAnchor).isActive = true;
    swiftImageView.bottomAnchor.constraint(equalTo: self.storyboardWrapperView.bottomAnchor).isActive = true;
    swiftImageView.leadingAnchor.constraint(equalTo: self.storyboardWrapperView.leadingAnchor).isActive = true;
    swiftImageView.trailingAnchor.constraint(equalTo: self.storyboardWrapperView.trailingAnchor).isActive = true;

当布局管理器试图满足冲突约束时，我在Xcode中看到的输出。

2017-05-17 22:45:18.351141-0700 My App[29787:7263069] [LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
    (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSAutoresizingMaskLayoutConstraint:0x170096670 h=--& v=--& UIImageView:0x101432d20.midX == 540   (active)>",
    "<NSLayoutConstraint:0x174092520 H:|-(0)-[UIView:0x101439120]   (active, names: '|':UIView:0x10142f4a0 )>",
    "<NSLayoutConstraint:0x174092570 H:[UIView:0x101439120]-(0)-|   (active, names: '|':UIView:0x10142f4a0 )>",
    "<NSLayoutConstraint:0x1740936a0 H:|-(0)-[UIImageView:0x101432d20]   (active, names: '|':UIView:0x101439120 )>",
    "<NSLayoutConstraint:0x174093790 UIImageView:0x101432d20.trailing == UIView:0x101439120.trailing   (active)>",
    "<NSLayoutConstraint:0x17009b260 'UIView-Encapsulated-Layout-Width' UIView:0x10142f4a0.width == 375   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x174093790 UIImageView:0x101432d20.trailing == UIView:0x101439120.trailing   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
2017-05-17 22:45:18.360996-0700 My App[29787:7263069] [LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
    (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<_UILayoutSupportConstraint:0x174091cb0 _UILayoutGuide:0x10143e8d0.height == 0   (active)>",
    "<_UILayoutSupportConstraint:0x174092930 V:|-(0)-[_UILayoutGuide:0x10143e8d0]   (active, names: '|':UIView:0x10142f4a0 )>",
    "<_UILayoutSupportConstraint:0x174091da0 _UILayoutGuide:0x10143ddc0.height == 0   (active)>",
    "<_UILayoutSupportConstraint:0x174091490 _UILayoutGuide:0x10143ddc0.bottom == UIView:0x10142f4a0.bottom   (active)>",
    "<NSAutoresizingMaskLayoutConstraint:0x17009cc50 h=--& v=--& UIImageView:0x101432d20.midY == 877.5   (active)>",
    "<NSLayoutConstraint:0x174092660 V:[_UILayoutGuide:0x10143e8d0]-(0)-[UIView:0x101439120]   (active)>",
    "<NSLayoutConstraint:0x1740927a0 V:[UIView:0x101439120]-(0)-[_UILayoutGuide:0x10143ddc0]   (active)>",
    "<NSLayoutConstraint:0x174093380 V:|-(0)-[UIImageView:0x101432d20]   (active, names: '|':UIView:0x101439120 )>",
    "<NSLayoutConstraint:0x174093650 UIImageView:0x101432d20.bottom == UIView:0x101439120.bottom   (active)>",
    "<NSLayoutConstraint:0x170098830 'UIView-Encapsulated-Layout-Height' UIView:0x10142f4a0.height == 667   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x174093650 UIImageView:0x101432d20.bottom == UIView:0x101439120.bottom   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

当我使用Xcode调试Debug View Hierarchy

时

以下链接图片显示：

父包装器UIView的约束。
通过故事板创建的UIImageView的约束。
通过Swift创建的UIImageView的约束。

constraint values

Answer 1

在您的控制台日志中，这两行告诉您发生了什么：

（注意：如果你看到NSAutoresizingMaskLayoutConstraints你不明白，请参阅UIView属性的文档 translatesAutoresizingMaskIntoConstraints）

NSAutoresizingMaskLayoutConstraint：0x17009cc50 h = - ＆amp; V = - ＆安培; UIImageView：0x101432d20.midY == 877.5（有效）

将此行添加到您的代码中将解决问题：

swiftImageView.translatesAutoresizingMaskIntoConstraints = false

UIImageView .scaleAspectFit和autolayout无法以编程方式从Swift工作

1 个答案: