在iOS开发中，可以通过设置UIStackView的distribution属性来实现变宽的StackView效果。具体方法是将distribution属性设置为.fillEqually并将StackView的子视图的contentHuggingPriority和contentCompressionResistancePriority设置为不同的值。例如，下面的示例代码创建了一个包含四个视图的水平StackView，其中第二个视图的宽度为其他三个视图的两倍：

let stackView = UIStackView()
stackView.axis = .horizontal
stackView.distribution = .fillEqually
view.addSubview(stackView)

let view1 = UIView()
let view2 = UIView()
let view3 = UIView()
let view4 = UIView()

// Set different contentHuggingPriority and contentCompressionResistancePriority values for the views
view1.setContentHuggingPriority(.defaultHigh, for: .horizontal)
view2.widthAnchor.constraint(equalTo: view1.widthAnchor, multiplier: 2).isActive = true
view3.setContentHuggingPriority(.defaultHigh, for: .horizontal)
view4.setContentHuggingPriority(.defaultHigh, for: .horizontal)

stackView.addArrangedSubview(view1)
stackView.addArrangedSubview(view2)
stackView.addArrangedSubview(view3)
stackView.addArrangedSubview(view4)