使用代码更新故事板约束

问题描述

我在代码中有一个 UIImage ，我想在按下按钮时垂直放大。 UIImage 在故事板中完全受限制，我想在按下按钮时更改其高度。

I have a UIImage in code that I would like to enlarge vertically when a button is pressed. The UIImage is fully constrained in the storyboard and I would like to change its height when the button is pressed.

我在代码中链接了 UIImage 及其高度约束：

I have linked the UIImage and its height constraint in the code:

    @IBOutlet weak var botBotCons: NSLayoutConstraint!
    @IBOutlet weak var botBot: UIImageView!

然后

@IBAction func testButton(sender: UIBarButtonItem) {
    println("testButton pressed")
    self.botBotCons.constant = 68   //or +=62 as its current constant is 6
    self.view.layoutIfNeeded()
}

我得到 testButton在控制台中按下消息，但图像不会调整大小。我究竟做错了什么？我是否还需要在故事板中更改某些内容？

I get the testButton pressed message in the console, but the image doesn't resize. What am I doing wrong? Do I need to change something in the storyboard as well?

推荐答案

您应该调用 layoutIfNeeded 在动画块中。 Apple实际上建议您在动画块之前调用一次，以确保所有挂起的布局操作都已完成。我只是通过调整按钮大小来检查它 - 一切正常。

You should to call layoutIfNeeded within the animation block. Apple actually recommends you call it once before the animation block to ensure that all pending layout operations have been completed. I just checked it with the resizing of button - everything works fine.

@IBOutlet weak var myBtn: UIButton!
@IBOutlet weak var btnHeight: NSLayoutConstraint!
@IBOutlet weak var btnWidth: NSLayoutConstraint!


@IBAction func resizeBtn(sender: AnyObject) {
    self.myBtn.titleEdgeInsets = UIEdgeInsetsMake(0, 0, 0, 0)

    self.view.layoutIfNeeded()
    self.btnHeight.constant += 50
    self.btnWidth.constant += 50

    UIView.animateWithDuration(0.7, animations: {
        self.view.layoutIfNeeded()
    })
}

PS确保其他约束不会阻止您的更改。

P.S. make sure that other constraints don't block your changes.

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