Set the center of a UIButton programmatically - SW

问题:

I have a UIButton inside a UIView, my UIButton has constraints which I set in storyboard. Now, I want to set the center of the UIButton at the center of the UIView. How will I do that programmatically?

回答1:

Try .center property like

myButton.center = self.view.center

You can also specify x and y If you need.

myButton.center.x = self.view.center.x // for horizontal
myButton.center.y = self.view.center.y // for vertical

回答2:

This approach is using Using NSLayoutConstraint where self.cenBut is the IBoutlet for your button.

func setupConstraints() {
    let centerX = NSLayoutConstraint(item: self.cenBut, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: self.view, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0)
    let centerY = NSLayoutConstraint(item: self.cenBut, attribute: NSLayoutAttribute.CenterY, relatedBy: NSLayoutRelation.Equal, toItem: self.view, attribute: NSLayoutAttribute.CenterY, multiplier: 1, constant: 0)
    let height = NSLayoutConstraint(item: self.cenBut, attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1, constant: 22)
    self.cenBut.translatesAutoresizingMaskIntoConstraints = false
    self.view.addConstraints([centerX, centerY, height])
}

In viewDidLoad()

self.view.removeConstraints(self.view.constraints)
self.setupConstraints()

回答3:

I should be

yourButton.setCenter(self.view.center);

But keep in mind that if you programmatically set the frame of a view, your layout constraints might not work as intended.

回答4:

since you are using constraints, you won't be able to set the center so you need to use constraints to set the center as well:

    let centerYCon = NSLayoutConstraint(item: labelMessage,
        attribute: .CenterY,
        relatedBy: .Equal,
        toItem: contentView,
        attribute: .CenterY,
        multiplier: 1.0,
        constant: 0.0);
    contentView.addConstraint(centerYCon);


    let centerXCon = NSLayoutConstraint(item: labelMessage,
        attribute: .CenterX,
        relatedBy: .Equal,
        toItem: contentView,
        attribute: .CenterX,
        multiplier: 1.0,
        constant: 0.0);
    contentView.addConstraint(centerXCon);

I'm assuming that you know what "programmatically" means with autolayout constraints. If you are truly using autolayout then you must have set the properties of your button to setTranslatesAutoresizingMaskIntoConstraints to false.