UILabel slides down to send error message - ios

Question

I want to add a UILabel to the view which slides down when an error occurs to send error message to user. The prototype of it is like the one Facebook or Instagram shows. Here is the codes I have worked out so far:
func sendErrorMessage(errorString: String) {
self.errorLabel.text = errorString
UIView.animateWithDuration(1, animations: {
self.errorLabel.frame.height = 30 //Cannot assign to the result of this expression
self.topView.layoutIfNeeded()
}, completion: {
(finished: Bool) in var timer = NSTimer.scheduledTimerWithTimeInterval(3, target: self, selector: Selector(), userInfo: nil, repeats: false)
})
}
errorLabel is now already in storyboard but with the height of 0 and topView is the superview of errorLabel. I am quite new to these methods so I am stuck here. I don't understand why that error occurred and what the selector should do here. There is also a step that I haven't done here that the errorLabel should slide up to disappear after three seconds and that's why I need a timer here.
Plus: Is there any difference if I create a new errorLabel whenever it is needed instead of make it ready before in storyboard? I mean in app performance of memory management.
UPDATE
I need errorLabel in many ViewControllers, so following the idea of #Sajjon, I tried to subclass UILabel. Here is my subclass ErrorLabel:
class ErrorLabel: UILabel {
var errorString: String?
func sendErrorMessage() {
self.text = errorString
showErrorLabel()
let timer = NSTimer.scheduledTimerWithTimeInterval(3, target: self, selector: "hideErrorLabel", userInfo: nil, repeats: false)
}
func animateFrameChange() {
UIView.animateWithDuration(1, animations: { self.layoutIfNeeded() }, completion: nil)
}
func showErrorLabel() {
let oldFrame = self.frame
let newFrame = CGRectMake(oldFrame.origin.x, oldFrame.origin.y, oldFrame.height + 30, oldFrame.width)
self.frame = newFrame
self.animateFrameChange()
}
func hideErrorLabel() {
let oldFrame = self.frame
let newFrame = CGRectMake(oldFrame.origin.x, oldFrame.origin.y, oldFrame.height - 30, oldFrame.width)
self.frame = newFrame
self.animateFrameChange()
}
}

Answer 1

Generally speaking, CGRect objects used by views for their frame or bounds properties are immutable. Instead of trying to directly modify the view's frame, create a new CGRect which contains the desired final size and position and assign that to the view's frame in the animation block.
//Don't do this.
myView.frame.size.height = 30;
// Do this instead.
CGRect oldRect = myView.frame;
CGRect newFrame = CGRectMake(oldRect.origin.x, oldRect.origin.y, oldRect.size.width, 30);
[UIView animateWithDuration:0.4 animations:^{
myView.frame = newFrame;
};
Also, I would strongly suggest making the label show and hide my changing its y position on and off the top of the screen, rather than changing the height to 0, which can have some unintended layout consequences

Answer 2

You ought to use autolayout for this, when showing the errorLabel (or some container view that it is inside), I would give the height constraint your wished value (30). And hiding it again by giving the constraint a value of 0.
I would create an UIView extension and put code for animating this height change.
This is untested code, but will give you an idea of how to achieve it.
class MyViewController: UIViewController {
#IBOutlet weak var errorLabelHeightConstraint: NSLayoutConstraint!
private let errorLabelHeightVisible: CGFloat = 30
private let hideDelay: NSTimeInterval = 3
private var timer: NSTimer!
func sendErrorMessage(errorString: String) {
errorLabel.text = errorString
showOrHideErrorView(false)
}
func showOrHideErrorView(hide: Bool = true, animated: Bool = true) {
if hide {
errorLabelHeightConstraint.constant = 0
} else {
errorLabelHeightConstraint.constant = errorLabelHeightVisible
}
let automaticallyHideErrorViewClosure: () -> Void = {
/* Only scheduling hiding of error message, if we just showed it. */
if !hide {
dispatch_async(dispatch_get_main_queue(), {
() -> Void in
automaticallyHideErrorMessage()
})
}
}
if animated {
view.animateConstraintChange(completion: {
(finished: Bool) -> Void in
automaticallyHideErrorViewClosure()
})
} else {
view.layoutIfNeeded()
automaticallyHideErrorViewClosure()
}
}
/* Selector method */
func hideError() {
showOrHideErrorView()
}
func automaticallyHideErrorMessage() {
if timer != nil {
if timer.valid {
timer.invalidate()
}
timer = nil
}
timer = NSTimer.scheduledTimerWithTimeInterval(hideDelay, target: self, selector: "hideError", userInfo: nil, repeats: false)
}
}
extension UIView {
static var standardDuration: NSTimeInterval { get { return 0.3 } }
func animateConstraintChange(duration: NSTimeInterval = standardDuration, completion: ((Bool) -> Void)? = nil) {
UIView.animate(durationUsed: duration, animations: {
() -> Void in
self.layoutIfNeeded()
}, completion: completion)
}
}

Answer 3

you need to set Frame of UILable instead of its height only.
func sendErrorMessage(errorString: String) {
self.errorLabel.text = errorString
UIView.animateWithDuration(1, animations: {
self.errorLabel.setFrame = CGRectmake(self.errorLabel.frame.origin.x,self.errorLabel.frame.origin.y,self.errorLabel.frame.size.width,30)
self.topView.layoutIfNeeded()
}, completion: {
(finished: Bool) in var timer = NSTimer.scheduledTimerWithTimeInterval(3, target: self, selector: Selector(), userInfo: nil, repeats: false)
})
}

Answer 4

For Change height Try This:
self.errorLabel.frame.size.height = 30