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IOS - 自動布局

簡介

iOS 6.0中引入的自動布局,我們隻能支持6.0和更高的部署目標。它可以幫助我們創建接口,可用於多個方向和多個設備。

 

我們例子的目標

我們將添加兩個按鈕,將屏幕的中心一定距離放置。我們也將嘗試將放置有一定距離,從上麵的按鈕,添加一個可調整大小的文本字段。

我們的方案

我們將添加文本字段和兩個按鈕的代碼,隨著它們的約束。每個UI元素的約束將被創建並添加超級視圖,並為我們添加的每一個UI元素,以獲得所需的結果,我們將關閉自動調整大小。

涉及的步驟

1. 創建一個簡單的應用程序。

2.我們將隻修改 ViewController.m 的文件內容,它是如下:

#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

我們在這裡做的是什麼呢?

在標有1,5和8的步驟,我們隻是以編程方式添加兩個按鈕和一個文本字段。在其餘的步驟中,我們創建約束,這些約束各自的超視圖(supper view),這實際上是self.view。當看著左邊的按鈕,如下圖所示的約束之一

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

實際上,我們有constraintWithItem 和 toItem之間決定的UI元素,我們創建約束。該屬性決定在什麼樣的基礎上,這兩個元素聯係在一起。關係決定屬性有多少元素之間的效果。乘法器的乘法係數和常數將被添加到乘數。在這裡,X的左鍵總是大於或等於-60像素相對於超視圖的中心。同樣,其他約束的定義。

輸出

現在,當我們運行應用程序在iPhone模擬器,我們將得到下麵的輸出。

iOS Tutorial

當我們改變方向的模擬器觀察方向,我們將得到下麵的輸出。

iOS Tutorial

當我們iPhone 5的模擬器上運行相同的應用程序,我們將得到下麵的輸出。

iOS Tutorial

當我們改變方向的模擬器觀察方向,我們將得到下麵的輸出。

iOS Tutorial