iOS自动布局


iOS 6.0 中引入了自动布局 当我们使用自动布局时,我们的部署目标应该是6.0或更高。自动布局有助于我们创建可用于多个方向和多个设备的接口。

我们的例子的目标

我们将添加两个按钮,这些按钮将放置在离屏幕中心一定距离处。我们还将尝试添加一个可调整大小的文本字段,该字段将从按钮上方的某个距离放置。

我们的方法

我们将在代码中添加一个文本字段和两个按钮及其约束。将创建每个UI元素的约束并将其添加到超级视图中。我们必须为我们添加的每个UI元素禁用自动调整大小以获得所需的结果。

涉及的步骤

第1步 - 创建一个简单的基于视图的应用程序。

第2步 - 我们将只编辑ViewController.m,它如下 -

#import "ViewController.h"
@interface ViewController ()
@property (nonatomic, strong) UIButton *leftButton;
@property (nonatomic, strong) UIButton *rightButton;
@property (nonatomic, strong) UITextField *textfield;

@end
@implementation ViewController

- (void)viewDidLoad {
   [super viewDidLoad];
   UIView *superview = self.view;

   /*1. Create leftButton and add to our view*/
   self.leftButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
   self.leftButton.translatesAutoresizingMaskIntoConstraints = NO;
   [self.leftButton setTitle:@"LeftButton" forState:UIControlStateNormal];
   [self.view addSubview:self.leftButton];

   /* 2. Constraint to position LeftButton's X*/
   NSLayoutConstraint *leftButtonXConstraint = [NSLayoutConstraint
   constraintWithItem:self.leftButton attribute:NSLayoutAttributeCenterX
   relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview attribute:
   NSLayoutAttributeCenterX multiplier:1.0 constant:-60.0f];

   /* 3. Constraint to position LeftButton's Y*/
   NSLayoutConstraint *leftButtonYConstraint = [NSLayoutConstraint
   constraintWithItem:self.leftButton attribute:NSLayoutAttributeCenterY
   relatedBy:NSLayoutRelationEqual toItem:superview attribute:
   NSLayoutAttributeCenterY multiplier:1.0f constant:0.0f];

   /* 4. Add the constraints to button's superview*/
   [superview addConstraints:@[ leftButtonXConstraint,
   leftButtonYConstraint]];

   /*5. Create rightButton and add to our view*/
   self.rightButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
   self.rightButton.translatesAutoresizingMaskIntoConstraints = NO;
   [self.rightButton setTitle:@"RightButton" forState:UIControlStateNormal];
   [self.view addSubview:self.rightButton];

   /*6. Constraint to position RightButton's X*/
   NSLayoutConstraint *rightButtonXConstraint = [NSLayoutConstraint
   constraintWithItem:self.rightButton attribute:NSLayoutAttributeCenterX
   relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview attribute:
   NSLayoutAttributeCenterX multiplier:1.0 constant:60.0f];

   /*7. Constraint to position RightButton's Y*/
   rightButtonXConstraint.priority = UILayoutPriorityDefaultHigh;
   NSLayoutConstraint *centerYMyConstraint = [NSLayoutConstraint
   constraintWithItem:self.rightButton attribute:NSLayoutAttributeCenterY
   relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview attribute:
   NSLayoutAttributeCenterY multiplier:1.0f constant:0.0f];
   [superview addConstraints:@[centerYMyConstraint,
   rightButtonXConstraint]];

   //8. Add Text field
   self.textfield = [[UITextField alloc]initWithFrame:
   CGRectMake(0, 100, 100, 30)];
   self.textfield.borderStyle = UITextBorderStyleRoundedRect;
   self.textfield.translatesAutoresizingMaskIntoConstraints = NO;
   [self.view addSubview:self.textfield];

   //9. Text field Constraints
   NSLayoutConstraint *textFieldTopConstraint = [NSLayoutConstraint
   constraintWithItem:self.textfield attribute:NSLayoutAttributeTop
   relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview
   attribute:NSLayoutAttributeTop multiplier:1.0 constant:60.0f];
   NSLayoutConstraint *textFieldBottomConstraint = [NSLayoutConstraint
   constraintWithItem:self.textfield attribute:NSLayoutAttributeTop
   relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:self.rightButton
   attribute:NSLayoutAttributeTop multiplier:0.8 constant:-60.0f];
   NSLayoutConstraint *textFieldLeftConstraint = [NSLayoutConstraint
   constraintWithItem:self.textfield attribute:NSLayoutAttributeLeft
   relatedBy:NSLayoutRelationEqual toItem:superview attribute:
   NSLayoutAttributeLeft multiplier:1.0 constant:30.0f];
   NSLayoutConstraint *textFieldRightConstraint = [NSLayoutConstraint
   constraintWithItem:self.textfield attribute:NSLayoutAttributeRight
   relatedBy:NSLayoutRelationEqual toItem:superview attribute:
   NSLayoutAttributeRight multiplier:1.0 constant:-30.0f];
   [superview addConstraints:@[textFieldBottomConstraint ,
   textFieldLeftConstraint, textFieldRightConstraint,
   textFieldTopConstraint]];
}

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

注意事项

在标记为1,5和8的步骤中,我们分别以编程方式添加了两个按钮和一个文本字段。

在其余步骤中,我们创建了约束并将这些约束添加到相应的超级视图中,这些视图实际上是自我视图。其中一个左按钮的约束如下所示 -

NSLayoutConstraint *leftButtonXConstraint = [NSLayoutConstraint
constraintWithItem:self.leftButton attribute:NSLayoutAttributeCenterX
relatedBy:NSLayoutRelationGreaterThanOrEqual toItem:superview attribute:
NSLayoutAttributeCenterX multiplier:1.0 constant:-60.0f];

我们有constraintWithItem和toItem,它们决定我们在创建约束的UI元素之间。该属性决定两个元素链接在一起的基础。“relatedBy”决定了属性在元素之间的影响程度。乘数是乘法因子,常数将被添加到乘法器。

在上面的例子中,leftButton的X总是相对于超视图的中心大于或等于-60像素。类似地,定义了其他约束。

输出

当我们运行应用程序时,我们将在iPhone模拟器上获得以下输出

iOS教程

当我们将模拟器的方向更改为横向时,我们将获得以下输出

iOS教程

当我们在iPhone 5模拟器上运行相同的应用程序时,我们将获得以下输出

iOS教程

当我们将模拟器的方向更改为横向时,我们将获得以下输出

iOS教程