ios自动布局另一个视图（分层）的边缘上的叠加视图

Question

在这里，我设计了一个自定义箭头，它将用作共享按钮。 如图所示，它应该固定在下边缘，其中心点固定在底视图上。

我将如何使用VFL做到这一点？

这就是我尝试的

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-10-[_whiteSquare(160)]-10-|"
                                                                  options:NSLayoutFormatDirectionLeadingToTrailing
                                                                  metrics:nil
                                                                    views:elementDict]];


[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[_shareButton(45)]-|"
                                                                  options:NSLayoutFormatDirectionLeadingToTrailing
                                                                  metrics:nil
                                                                    views:elementDict]];


[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[_shareButton(45)]-20-|"
                                                                  options:NSLayoutFormatDirectionLeadingToTrailing
                                                                  metrics:nil
                                                                    views:elementDict]];



[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-10-[_whiteSquare]-10-|"
                                                                  options:NSLayoutFormatDirectionLeadingToTrailing
                                                                  metrics:nil
                                                                    views:elementDict]];

将whiteSquare和shareButton都附加到shareButton视图。 但这只是将shareButton放在shareButton视图的底部，而不是中心固定在whiteSquare的底部

Answer 1

您应该相对于白色正方形而不是超级视图放置共享按钮

这应该可以解决问题：

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-10-[_whiteSquare(160)]-10-|"
                                                                  options:NSLayoutFormatDirectionLeadingToTrailing
                                                                  metrics:nil
                                                                    views:elementDict]];


[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[_whiteSquare]-22.5-[_shareButton(45)]"
                                                                  options: NSLayoutFormatDirectionRightToLeft
                                                                  metrics:nil
                                                                    views:elementDict]];


[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-10-[_whiteSquare]-10-|"
                                                                  options:NSLayoutFormatDirectionLeadingToTrailing
                                                                  metrics:nil
                                                                    views:elementDict]];

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[_whiteSquare]-22.5-[_shareButton(45)]"
                                                                  options:NSLayoutFormatDirectionRightToLeft
                                                                  metrics:nil
                                                                    views:elementDict]];