Question

我有一个UITableViewCell的子类，它使用AutoLayout并通过UITableView registerNib(nib: UINib, forCellReuseIdentifier: String)和dequeueReusableCellWithIdentifier(identifier: String)重用。单元格有两个按钮，我在layoutSubviews()上设置了AutoLayout约束：

override func layoutSubviews()
{
    super.layoutSubviews()

        //Clear all constraints from the cell
        self.contentView.removeConstraints(self.contentView.constraints())
        self.oneButton.setTranslatesAutoresizingMaskIntoConstraints(false)
        self.twoButton.setTranslatesAutoresizingMaskIntoConstraints(false)

        let viewsDict : [NSObject: AnyObject] = ["oneButton" : self.oneButton, "twoButton": self.twoButton]

        //Setting the constraints
        self.contentView.addConstraint(NSLayoutConstraint(item: self.oneButton, attribute: NSLayoutAttribute.Width, relatedBy: NSLayoutRelation.Equal, toItem: self.twoButton, attribute: NSLayoutAttribute.Width, multiplier: 1.0, constant: 0.0))
        self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-25-[oneButton]-25-[twoButton]-25-|", options: NSLayoutFormatOptions(0), metrics: nil, views: viewsDict))
        self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-25-[oneButton(40)]-25-|", options: NSLayoutFormatOptions(0), metrics: nil, views: viewsDict))
        self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-25-[twoButton(40)]-25-|", options: NSLayoutFormatOptions(0), metrics: nil, views: viewsDict))
}

这仅适用于第一次实例化单元格。重复使用后，水平间距和尺寸确定中断。在玩完并设置断点之后，我发现在updateConstraints之后调用了layoutSubviews，并且只在第一次实例化单元格时，而不是在重用之后。

稍微摆弄一下后我尝试了这个：

override func updateConstraints()
{
    super.updateConstraints()
    self.hasUpdated = true
}

override func layoutSubviews()
{
    super.layoutSubviews()

    if (!self.hasUpdated)
    {
        //Clear all constraints from the cell
        self.contentView.removeConstraints(self.contentView.constraints())
        self.oneButton.setTranslatesAutoresizingMaskIntoConstraints(false)
        self.twoButton.setTranslatesAutoresizingMaskIntoConstraints(false)

        let viewsDict : [NSObject: AnyObject] = ["oneButton" : self.oneButton, "twoButton": self.twoButton]

        //Setting the constraints
        self.contentView.addConstraint(NSLayoutConstraint(item: self.oneButton, attribute: NSLayoutAttribute.Width, relatedBy: NSLayoutRelation.Equal, toItem: self.twoButton, attribute: NSLayoutAttribute.Width, multiplier: 1.0, constant: 0.0))
        self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-25-[oneButton]-25-[twoButton]-25-|", options: NSLayoutFormatOptions(0), metrics: nil, views: viewsDict))
        self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-25-[oneButton(40)]-25-|", options: NSLayoutFormatOptions(0), metrics: nil, views: viewsDict))
        self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-25-[twoButton(40)]-25-|", options: NSLayoutFormatOptions(0), metrics: nil, views: viewsDict))
    }
}

现在它按预期工作，但我觉得我可能会禁止一些重用布局机制，因为我并不总是设置约束。有什么想法吗？

编辑：在Shai发表评论后，我认为removeConstraints和setTranslatesAutoresizingMaskIntoConstraints来电可能是罪魁祸首。我所做的就是停止覆盖layoutSubviews并将其更改为：

override func awakeFromNib()
{
    super.awakeFromNib()

    self.contentView.removeConstraints(self.contentView.constraints())
    self.oneButton.setTranslatesAutoresizingMaskIntoConstraints(false)
    self.twoButton.setTranslatesAutoresizingMaskIntoConstraints(false)
    // Initialization code
}

override func updateConstraints()
{
    super.updateConstraints()

    let viewsDict : [NSObject: AnyObject] = ["oneButton" : self.oneButton, "twoButton": self.twoButton]

    //Setting the constraints
    self.contentView.addConstraint(NSLayoutConstraint(item: self.oneButton, attribute: NSLayoutAttribute.Width, relatedBy: NSLayoutRelation.Equal, toItem: self.twoButton, attribute: NSLayoutAttribute.Width, multiplier: 1.0, constant: 0.0))
    self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-25-[oneButton]-25-[twoButton]-25-|", options: NSLayoutFormatOptions(0), metrics: nil, views: viewsDict))
    self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-25-[oneButton(40)]-25-|", options: NSLayoutFormatOptions(0), metrics: nil, views: viewsDict))
    self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-25-[twoButton(40)]-25-|", options: NSLayoutFormatOptions(0), metrics: nil, views: viewsDict))
}

现在我觉得不喜欢黑客重用机制......还有，对此有什么看法吗？

UITableViewCell子类上的AutoLayout在重用后中断

0 个答案: