How correct add and show UIView on tap - ios

Question

I try show checkmark(GitHub WVCheckMark) when i tap on button. Here is code, and it work only when i tap on button second time.
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
mark = [[WVCheckMark alloc] init];//WithFrame:CGRectMake(50, 50, 100, 100)];
mark.backgroundColor = [UIColor clearColor];
//[mark setFrame:CGRectMake(100, 100, 100, 100)];
//[self.view addSubview:mark];
}
- (IBAction) btnShow{
[mark setFrame:CGRectMake(100, 100, 100, 100)];
[self.view addSubview:mark];
[mark setNeedsDisplay];
[mark updateConstraints];
[mark setNeedsLayout];
[mark start];
}
It's work how i want (tap and show) if use addSubview in viewDidLoad.
Calling this methods don't help.
[mark setNeedsDisplay];
[mark updateConstraints];
[mark setNeedsLayout];
Is it possible add subview and show it in one place of code?
Full code
#import "ViewController.h"
#import "TestCheckmark-Swift.h"
#interface ViewController ()
#end
WVCheckMark *mark;
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
mark = [[WVCheckMark alloc] initWithFrame:CGRectMake(50, 50, 100, 100)];
mark.backgroundColor = [UIColor clearColor];
[mark setFrame:CGRectMake(100, 100, 100, 100)];
//[self.view addSubview:mark];
}
- (IBAction) btnShow{
//[mark setFrame:CGRectMake(100, 100, 100, 100)];
//[self.view addSubview:mark];
[mark setNeedsDisplay];
[mark updateConstraints];
[mark setNeedsLayout];
[mark start];
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
#end

Answer 1

Short answer: the OP code doesn't need to call setNeedsDisplay, setNeedsLayout, updateConstraints on the added view, but it does need to call addSubview: on the parent view, as in [self.view addSubview:mark];
But to go a little deeper, it looks like WVCheckMark on GitHub is a subclass of UIView. That's a good, important thing because it means we can probably count on some desirable stuff inherited from UIView.
For example, the .alpha property, which is a good way to alter visibility without messing around with the view hierarchy (adding and removing child views). Another nice thing about .alpha is that -- unlike .hidden -- alpha can be animated.
So let's setup the view hierarchy and framing in one place. The key idea -- and the idea probably most confounding the OP code -- is to call addSubview:. Doing the setup lazily is a good way to insure we do it exactly once, at the point we need to.
- (WVCheckMark *)mark {
WVCheckMark *mark = [self.view viewWithTag:64]; // 64 must be non-zero and unique amongst self.view subviews
if (!mark) {
mark = [[WVCheckMark alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];
mark.tag = 64; // so we can find it later
mark.backgroundColor = [UIColor clearColor];
// start out invisible
mark.alpha = 0.0;
// important, addSubview, which is probably the main problem in the OP
[self.view addSubview:mark];
}
return mark;
}
Now, whenever you need to show/hide that view, just do this:
self.mark.alpha = 1.0; // show
self.mark.alpha = 0.0; // hide
Since that property is animatable, you can get a little fancy fade like this:
- (void)setMarkHidden:(BOOL)hidden animated:(BOOL)animated {
NSTimeInterval duration = (animated)? 0.3 : 0.0;
CGFloat alpha = (hidden)? 0.0 : 1.0;
[UIView animateWithDuration:duration animations:^{
self.mark.alpha = alpha;
}];
}
You can throw away all of your other check mark related code, and just do this when the button is pressed to trigger the appearance...
- (IBAction)pressed:(id)sender {
[setMarkHidden:YES animated:YES];
}