自动布局和约束问题

Question

我遇到了 iOS 和 AutoLayout 的问题...这是一个测试应用程序，我在其中复制了问题。它包含一个简单的视图控制器，包含一个固定的UIButton；当用户单击此按钮时，委托必须创建一个自定义视图，对其应用定位约束；然后视图有一个方法来构建他的内容视图，并且子视图也被放置了约束。

代码如下：

//MyViewController.m

@implementation MyViewController

- (void)viewDidLoad
{
  [super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.

  UIButton *start_but = [[UIButton alloc] initWithFrame:CGRectMake(10, 10, 100, 40)];
  [start_but setTitle:@"Draw" forState:UIControlStateNormal];
  [start_but setTitleColor:[UIColor yellowColor] forState:UIControlStateNormal];
  [start_but addTarget:self action:@selector(clickAction:) forControlEvents:UIControlEventTouchUpInside];

  [self.view addSubview:start_but];
}

- (void)didReceiveMemoryWarning
{
  [super didReceiveMemoryWarning];
  // Dispose of any resources that can be recreated.
}

- (void)clickAction: (id)sender
{

  localView = [[MyView alloc] initWithFrame:CGRectMake(0, 0, 400, 300)];

  UIView *superview = (UIView*)localView;

  superview.translatesAutoresizingMaskIntoConstraints = NO;

  [self.view addSubview:localView];

  NSLayoutConstraint *constr = [NSLayoutConstraint constraintWithItem:localView
                                                          attribute:NSLayoutAttributeTop
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:self.view
                                                          attribute:NSLayoutAttributeTop
                                                         multiplier:1.0
                                                           constant:100.0];

  [self.view addConstraint:constr];

  constr = [NSLayoutConstraint constraintWithItem:localView
                                                          attribute:NSLayoutAttributeRight
                                                          relatedBy:NSLayoutRelationEqual
                                                             toItem:self.view
                                                          attribute:NSLayoutAttributeRight
                                                         multiplier:1.0
                                                           constant:-50.0];
  [self.view addConstraint:constr];



  [localView CreateGuiInterface];
}

@end


//MyView.m


@implementation MyView

- (id)initWithFrame:(CGRect)frame
{
  self = [super initWithFrame:frame];
  if (self)
  {
    // Initialization code



  }
  return self;
}

-(void)CreateGuiInterface
{
  UIView *superview = self;

  self.backgroundColor = [UIColor redColor];

  UIButton *but1 = [[UIButton alloc] init];
  [but1 setTitle:@"Button" forState:UIControlStateNormal];
  [but1 setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
  but1.backgroundColor = [UIColor yellowColor];

  but1.translatesAutoresizingMaskIntoConstraints = NO;

  [superview addSubview:but1];

  NSLayoutConstraint *constraint = [NSLayoutConstraint constraintWithItem:but1
                                                              attribute:NSLayoutAttributeRight
                                                              relatedBy:NSLayoutRelationEqual
                                                                 toItem:superview
                                                              attribute:NSLayoutAttributeRight multiplier:1.0
                                                               constant:-20.0];

  [superview addConstraint:constraint];

  constraint = [NSLayoutConstraint constraintWithItem:but1
                                          attribute:NSLayoutAttributeTop
                                          relatedBy:NSLayoutRelationEqual
                                             toItem:superview
                                          attribute:NSLayoutAttributeTop
                                         multiplier:1.0
                                           constant:50.0];

  [superview addConstraint:constraint];

  UILabel *label = [[UILabel alloc] init];

  label.text = @"Label";
  label.backgroundColor = [UIColor greenColor];
  label.textColor = [UIColor blackColor];
  label.translatesAutoresizingMaskIntoConstraints = NO;

  [superview addSubview:label];

  constraint = [NSLayoutConstraint constraintWithItem:label
                                          attribute:NSLayoutAttributeRight
                                          relatedBy:NSLayoutRelationEqual
                                             toItem:but1
                                          attribute:NSLayoutAttributeLeft
                                         multiplier:1.0
                                           constant:-40.0];
  [superview addConstraint:constraint];

  constraint = [NSLayoutConstraint constraintWithItem:label
                                          attribute:NSLayoutAttributeTop
                                          relatedBy:NSLayoutRelationEqual
                                             toItem:but1
                                          attribute:NSLayoutAttributeBottom
                                         multiplier:1.0
                                           constant:20.0];

  [superview addConstraint:constraint];

} 

@end

所以，问题是当我单击 iOS 时似乎无法绘制视图背景颜色。这很奇怪，因为如果我不使用superview.translatesAutoresizingMaskIntoConstraints = NO 并将视图放在固定位置（例如initWithFrame:CGRect(100,200,300,400)）而不使用约束，它工作正常：在子视图和父视图中使用约束会出现问题? AppleDoc 表示约束不能通过视图屏障；所以我用面向本地视图的约束编写了我的应用程序...... 有人可以帮助我吗？

感谢您的建议

Answer 1

使用 autoLayout 的目的是永远不必在任何视图上设置框架。如果您想以编程方式将您的视图放置在您的超级视图中，您将为此提供约束。我所做的更改您将看到预期的红色背景。我没有更改您的 MyView 实现（只需添加 -(void)CreateGuiInterface; 在 MyView.h 中）。我为演示所做的更改在您的 MyViewController 实现中。

尝试使用以下代码代替您的 viewController：

@interface MyViewController ()
@property (nonatomic, strong) MyView* localView;
@end

@implementation MyViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    UIButton *start_but = [[UIButton alloc] init];
    start_but.translatesAutoresizingMaskIntoConstraints = NO;

    [start_but setTitle:@"Draw" forState:UIControlStateNormal];
    [start_but setTitleColor:[UIColor yellowColor] forState:UIControlStateNormal];
    [start_but addTarget:self action:@selector(clickAction:)  forControlEvents:UIControlEventTouchUpInside];

    [self.view addSubview:start_but];

    // The following constraints simply place the initial start button in the top left
    NSDictionary* views = NSDictionaryOfVariableBindings(start_but);
    NSString* format = @"H:|-[start_but]";
    NSArray* constraints = [NSLayoutConstraint constraintsWithVisualFormat:format
                                                                   options:0
                                                                   metrics:nil
                                                                     views:views];
    [self.view addConstraints:constraints];
    format = @"V:|-[start_but]";
    constraints = [NSLayoutConstraint constraintsWithVisualFormat:format
                                                          options:0
                                                          metrics:nil
                                                            views:views];
    [self.view addConstraints:constraints];
}

- (void)clickAction: (id)sender
{
    self.localView = [[MyView alloc] init];

    UIView *superview = (UIView*)self.localView;

    superview.translatesAutoresizingMaskIntoConstraints = NO;

    [self.view addSubview:self.localView];

    // Here I'm placing your parent view (MyView) 50 points on right of the superview with
    // a width of 400 points
    NSDictionary* views = NSDictionaryOfVariableBindings(superview);
    NSString* format = @"H:[superview(==400)]-(50)-|";
    NSArray* constraints = [NSLayoutConstraint constraintsWithVisualFormat:format
                                                                   options:0
                                                                   metrics:nil
                                                                     views:views];
    [self.view addConstraints:constraints];

    // Vertically 100 points from the top of the superview with a height of 300 points
    format = @"V:|-(100)-[superview(==300)]";
    constraints = [NSLayoutConstraint constraintsWithVisualFormat:format
                                                          options:0
                                                          metrics:nil
                                                            views:views];
    [self.view addConstraints:constraints];

    [self.localView CreateGuiInterface];
}

@end