自动布局以编程方式修改约束的乘数

Question

如何以编程方式修改约束的乘数？我已经设置了以下内容：

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:_button attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeWidth multiplier:0.5 constant:0.0]];

我需要修改它：

[self.view addConstraint:[NSLayoutConstraint constraintWithItem:_button attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeWidth multiplier:1.0 constant:0.0]];

Answer 1

您无法更改乘数，因为它是只读的。您必须存储对约束的引用。然后，当您想要更改乘数时，您将删除约束并添加一个新约束。

您可以在视图控制器实现中包含这样的方法：

  $scope.signInClick = function() {
    console.log('Login was clicked');
     
      $scope.loading = $ionicLoading.show({
          content: 'Logging in',
          animation: 'fade-in',
          showBackdrop: true,
          maxWidth: 200,
          showDelay: 0
      });

      var params = {'login': ($scope.user.username), 'password': ($scope.user.password)}
      console.log("params... " + JSON.stringify(params));

      QB.users.create(params, function(err, user){
        if (user) {
          console.log("successful user.create... " + JSON.stringify(user));
          var jid = user.id + "-23837" + "@chat.quickblox.com";
          console.log(user.login + "'s jid is......" + jid);
          var chatparams = {'jid': jid, 'password': ($scope.user.password)};
          QB.chat.connect(chatparams, function(err, roster) {
            console.log("err from qb.chat.connect... " + JSON.stringify(err));
            console.log("roster from qb.chat.connect .... " + JSON.stringify(roster));
          });
        } 
        else  {
          console.log(JSON.stringify(err));
          if (err.message == "Unprocessable Entity"){
            QB.login(params, function(err, user){
              if (user) {
                console.log("Logged into QB with " + JSON.stringify(user));
                var jid = user.id + "-23837" + "@chat.quickblox.com";
                console.log(user.login + "'s jid is......" + jid);
                var chatparams = {'jid': jid, 'password': ($scope.user.password)};
                QB.chat.connect(chatparams, function(err, roster) {
                  console.log("stringifying the err... " + JSON.stringify(err));
                  console.log("stringifying the roster... " + JSON.stringify(roster));
                });
              } 
              else  {
                console.log(JSON.stringify(err));
              }
            });
          }
        }
      });

相关问题：

Can i change multiplier property for NSLayoutConstraint?

Answer 2

正如其他人所说，你必须删除旧的并添加一个新的。如果您不想将其存储为属性，只需设置标识符并搜索以便稍后获取

-(NSLayoutConstraint *)constraintWithIndientifer:(NSString *)identifer InView:(UIView *)view{
    NSLayoutConstraint * constraintToFind = nil;
    for (NSLayoutConstraint * constraint in view.constraints ) {
        if([constraint.identifier isEqualToString:identifer]){
            constraintToFind = constraint;
            break;
        }
    }
    return constraintToFind;
}

然后

NSLayoutConstraint * constraint = [NSLayoutConstraint constraintWithItem:self.yellowView attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeWidth multiplier:0.5 constant:0.0];
constraint.identifier = @"1234";
[self.view addConstraint:constraint];

然后你可以得到这个

NSLayoutConstraint * constraint = [self constraintWithIndientifer:@"1234" InView:self.view];

Answer 3

对于修改乘数我使用约束方法之间的切换 您必须创建具有不同优先级的约束，否则它将破坏布局。

目标C

NSLayoutConstraint *constraint1, *constraint2;

// switch between constraints

constraint1.active = NO; 
constraint2.active = YES;
[self.view layoutIfNeeded];

Swift 2.0

self.constraint1.active = true
self.constraint2.active = false
self.view.layoutIfNeeded()

Answer 4

使用Layout Anchors以编程方式修改约束的乘数是一种更简单的方法：

imageView.heightAnchor.constraint(equalTo: imageView.widthAnchor, multiplier: 1.0/2.0).isActive = true

以下是它的工作原理：