自动布局Masonry更新约束

上一篇写了Masonry设置约束的基本使用，而实际开发中我们有时候不仅要加约束，还需要更新约束，所以本篇就专门来写下Masonry是如何更新约束的，其实很简单，Masonry中可以使用mas_updateConstraints来更新约束，也可以使用mas_remakeConstraints，两者的区别是update是更新约束，而remake会在添加约束前去掉之前的约束。大家可以根据自己的实际需求使用，我这里的例子用的是update来更新约束。

在一些APP中我们经常可以看到，尤其是登录界面，当键盘弹起时会遮挡到部分文本框，这个时候往往是将文本框的位置上移。本文中的小demo就是类似是这种功能，点击绿色的文本框，键盘弹出时让文本框移到键盘之上，结束编辑后又回到原位。

先看下效果图吧：

                        

首先，让我们来添加子控件：

/** 初始化子控件 */-(void)setupSubviews{    //文本框textview    UITextField *greenTextView=[[UITextField alloc]init];    greenTextView.backgroundColor = [UIColor greenColor];    greenTextView.placeholder = @"点我更新约束啦...";    self.greenTextView = greenTextView;    [self.view addSubview:greenTextView];        //设置初始时的约束    //左边距离self.view左边10    //底部距离self.view 20    //高度为50    //宽度自适应    [greenTextView mas_makeConstraints:^(MASConstraintMaker *make) {        make.leading.equalTo(self.view.mas_leading).offset(10);        make.bottom.equalTo(self.view.mas_bottom).offset(-20);        make.height.mas_equalTo(50);    }];        //按钮    UIButton *blueBtn = [[UIButton alloc]init];    blueBtn.backgroundColor = [UIColor blueColor];    self.blueBtn = blueBtn;    [self.view addSubview:blueBtn];        //设置初始时的约束    //右边距离self.view右边10    //左边距离self.greenTextView右边 10    //宽高和self.greenTextView一样    [blueBtn mas_makeConstraints:^(MASConstraintMaker *make) {        make.trailing.equalTo(self.view.mas_trailing).offset(-10);        make.leading.equalTo(self.greenTextView.mas_trailing).offset(10);        make.bottom.equalTo(self.greenTextView.mas_bottom);        make.size.equalTo(self.greenTextView);    }];}

接下来就是在监听键盘弹出的方法里更新约束了，注释都写在代码里了。

//键盘弹出时会调用-(void)keyboardWillShow:(NSNotification *)notification{    //获取键盘的基本信息    NSDictionary *userInfo = [notification userInfo];    CGRect rect = [userInfo[UIKeyboardFrameBeginUserInfoKey] CGRectValue];        CGFloat keyboardHeight = CGRectGetHeight(rect);    CGFloat duration = [userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];        //修改下边距约束    [self.greenTextView mas_updateConstraints:^(MASConstraintMaker *make) {        make.bottom.mas_equalTo(-keyboardHeight-20);    }];        //更新约束    [UIView animateWithDuration:duration animations:^{        [self.view layoutIfNeeded];    }];}

这样就实现了当点击文本框编辑时，文本框上移的功能了。收回键盘的代码跟弹出的一样，这里不单独拿出来了，文章最后会贴上完整的代码。

注意添加监听以及导入Masonry哦，否则导入头文件是会报错的，是不是很简单！

好了，需要完整代码的童鞋看这里吧：

#import "ViewController.h"#import "Masonry.h"@interface ViewController ()@property(nonatomic,strong)UITextField *greenTextView;@property(nonatomic,strong)UIButton *blueBtn;@end@implementation ViewController- (void)viewDidLoad {    [super viewDidLoad];        //初始化子控件    [self setupSubviews];        //键盘弹出监听    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillShow:) name:UIKeyboardWillShowNotification object:nil];    //键盘收回监听    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardWillHidden:) name:UIKeyboardWillHideNotification object:nil];}/** 初始化子控件 */-(void)setupSubviews{    //文本框textview    UITextField *greenTextView=[[UITextField alloc]init];    greenTextView.backgroundColor = [UIColor greenColor];    greenTextView.placeholder = @"点我更新约束啦...";    self.greenTextView = greenTextView;    [self.view addSubview:greenTextView];        //设置初始时的约束    //左边距离self.view左边10    //底部距离self.view 20    //高度为50    //宽度自适应    [greenTextView mas_makeConstraints:^(MASConstraintMaker *make) {        make.leading.equalTo(self.view.mas_leading).offset(10);        make.bottom.equalTo(self.view.mas_bottom).offset(-20);        make.height.mas_equalTo(50);    }];        //按钮    UIButton *blueBtn = [[UIButton alloc]init];    blueBtn.backgroundColor = [UIColor blueColor];    self.blueBtn = blueBtn;    [self.view addSubview:blueBtn];        //设置初始时的约束    //右边距离self.view右边10    //左边距离self.greenTextView右边 10    //宽高和self.greenTextView一样    [blueBtn mas_makeConstraints:^(MASConstraintMaker *make) {        make.trailing.equalTo(self.view.mas_trailing).offset(-10);        make.leading.equalTo(self.greenTextView.mas_trailing).offset(10);        make.bottom.equalTo(self.greenTextView.mas_bottom);        make.size.equalTo(self.greenTextView);    }];}//键盘弹出时会调用-(void)keyboardWillShow:(NSNotification *)notification{    //获取键盘的基本信息    NSDictionary *userInfo = [notification userInfo];    CGRect rect = [userInfo[UIKeyboardFrameBeginUserInfoKey] CGRectValue];        CGFloat keyboardHeight = CGRectGetHeight(rect);    CGFloat duration = [userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];        //修改下边距约束    [self.greenTextView mas_updateConstraints:^(MASConstraintMaker *make) {        make.bottom.mas_equalTo(-keyboardHeight-20);    }];        //更新约束    [UIView animateWithDuration:duration animations:^{        [self.view layoutIfNeeded];    }];}//键盘收回时会调用-(void)keyboardWillHidden:(NSNotification *)notification{    NSDictionary *userInfo = [notification userInfo];    CGFloat duration = [userInfo[UIKeyboardAnimationDurationUserInfoKey] doubleValue];        //修改下边距约束    [self.greenTextView mas_updateConstraints:^(MASConstraintMaker *make) {        make.bottom.mas_equalTo(-20);    }];        //更新约束    [UIView animateWithDuration:duration animations:^{        [self.view layoutIfNeeded];    }];}-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{    //结束编辑    [self.view endEditing:YES];}@end