ios - 我的 UIButtonBarItem 's don' t 使用 FlexibleSpace 正确布局

Question

我正在以编程方式快速创建 UIToolBar 及其项目:

    var items = [UIBarButtonItem]()
    let leftButton  = UIBarButtonItem(image: UIImage(named: "left"), style: .Plain, target: self, action: Selector("doneClickedMaButton"))
    let spacer      = UIBarButtonItem(barButtonSystemItem: .FlexibleSpace, target: nil, action: nil)
    let rightButton = UIBarButtonItem(image: UIImage(named: "right"), style: .Plain, target: self, action: Selector("doneClickedRight"))
    let searchButton = UIBarButtonItem(barButtonSystemItem: .Search, target: self, action: Selector("doneClickedSearch"))
    items.append(leftButton)
    items.append(spacer)
    items.append(searchButton)
    items.append(spacer)        
    items.append(rightButton)

var toolBar         = UIToolbar()
    toolBar.frame = CGRectMake(0, 0, self.view.frame.size.width, 50)
    toolBar.translatesAutoresizingMaskIntoConstraints = false
    toolBar.backgroundColor = UIColor.redColor()
    toolBar.items = items
    toolBar.sizeToFit()
    view.addSubview(toolBar)
    view.addConstraint(NSLayoutConstraint(item: toolBar, attribute: .Bottom, relatedBy: .Equal, toItem: view, attribute: .Bottom, multiplier: 1.0, constant: 0.0))

如果我不添加 spacer 项，那么模拟器将如下所示:

如果我确实有它们，就像这段代码中所说的那样。我明白了:

正如您在这里所看到的，图像现在不仅从屏幕向左掉落，而且它们的顺序也不再正确。

我认为 .FlexibleSpace 只是在项目之间添加动态间距。我在这里错过了什么吗？有人在各种帖子中提到，可以在 UIBarButtonItem 中设置 UILabel 的宽度，这可以使 .FlexibleSpace 识别它。

Answer 1

问题是您没有足够的约束来满足自动布局引擎的要求。您将工具栏固定在底部，但宽度正在缩小，因此它只能容纳按钮，但您希望它是 View 的宽度。尝试类似的东西:

var items = [UIBarButtonItem]()
    let leftButton  = UIBarButtonItem(image: UIImage(named: "left"), style: .Plain, target: self, action: Selector("doneClickedMaButton"))
    let spacer      = UIBarButtonItem(barButtonSystemItem: .FlexibleSpace, target: nil, action: nil)
    let rightButton = UIBarButtonItem(image: UIImage(named: "right"), style: .Plain, target: self, action: Selector("doneClickedRight"))
    let searchButton = UIBarButtonItem(barButtonSystemItem: .Search, target: self, action: Selector("doneClickedSearch"))
    items.append(leftButton)
    items.append(spacer)
    items.append(searchButton)
    items.append(spacer)        
    items.append(rightButton)

var toolBar         = UIToolbar()
    toolBar.frame = CGRectMake(0, 0, self.view.frame.size.width, 50)
    toolBar.translatesAutoresizingMaskIntoConstraints = false
    toolBar.backgroundColor = UIColor.redColor()
    toolBar.items = items
    toolBar.sizeToFit()
    view.addSubview(toolBar)
    toolBar.leadingAnchor.constraintEqualToAnchor(self.view.leadingAnchor).active = true
    toolBar.trailingAnchor.constraintEqualToAnchor(self.view.trailingAnchor).active = true
    toolBar.bottomAnchor.constraintEqualToAnchor(self.view.bottomAnchor).active = true