resignFirstResponder changes frame value - ios

Question

I have a LoginViewController with two text fields and a button. I used storyboard, so these are not created programmatically. They are below each other.
Here's the .h file
#interface LoginViewController : UIViewController <UITextFieldDelegate>
#property (weak, nonatomic) IBOutlet UITextField *pw1;
#property (weak, nonatomic) IBOutlet UITextField *pw2;
#property (weak, nonatomic) IBOutlet UIButton *loginBtn;
- (IBAction)loginBtnPressed:(id)sender;
- (IBAction)singleTapRecognized:(id)sender;
#end
The pw2 is shown only on the first run, when the user creates a new password and confirms it in pw2. Otherwise it is hidden. In that case I move the button up to put the button closer to pw1.
CGSize size = self.pw2.frame.size;
CGRect rect = self.loginBtn.frame;
CGRect newFrame = CGRectMake(rect.origin.x, rect.origin.y-size.height, rect.size.width,rect.size.height);
[self.loginBtn setFrame:newFrame];
So far, so good. Up to here all works as expected. But now.....
when I leave the pw1 blank, the program checks the field, detects it is empty, hides the keyboard and shows a UIAlertView. This works fine.
when I put in some characters that are not correct, the program does almost the same, but moves the button down to its original position.
same behavior when some characters entered and tapped anywhere in the view
I found out, that this only happens, when I am hiding the keyboard. Otherwise the button stays at its "upped" position as expected.
Here is my keyboard hide:
-(void) hideKeyboard {
if (self.pw1.isFirstResponder)
[self.pw1 resignFirstResponder];
else if (self.pw2.isFirstResponder)
[self.pw2 resignFirstResponder];
}
Any ideas what happens?
Sorry about my english. English is not my native language.

Answer 1

I want to share my solution with you. I am sure there is a more elegant way to code, but this one works fine more me.
I added property in the .h file to hold the new constraint for the button.
#property NSLayoutConstraint *loginButtonVerticalSpace;
Then i add a routine to find the "old" constraint as defined in the storyboard.
-(NSLayoutConstraint *) findButtonConstraintForItem:(id) item
secondItem:(id) secondItem //may be nil
firstAttribute:(NSLayoutAttribute)firstAttribute
secondAttribute:(NSLayoutAttribute)secondAttribute
{
NSArray *cons = self.view.constraints;
for (NSLayoutConstraint *ns in cons) {
if (ns.firstItem==item)
{
if (ns.firstAttribute==firstAttribute)
{
if (secondItem==nil)
return ns;
if (ns.secondItem==secondItem && ns.secondAttribute==secondAttribute)
return ns;
}
}
}
return nil;
}
And at least i changed my "moveButton" method to the following:
- (void) moveButtonUp{
NSLayoutConstraint *consOld = [self findButtonConstraintForItem:self.loginBtn
secondItem:self.pw1
firstAttribute:NSLayoutAttributeTop
secondAttribute:NSLayoutAttributeBottom];
if (!consOld) // should not happen
return;
if (self.loginButtonVerticalSpace) // work already done
return;
CGSize size = self.pw2.frame.size;
self.loginButtonVerticalSpace =[NSLayoutConstraint
constraintWithItem:self.loginBtn
attribute:NSLayoutAttributeTop
relatedBy:NSLayoutRelationEqual
toItem:self.pw1
attribute:NSLayoutAttributeBottom
multiplier:1.0
constant:consOld.constant-size.height];
self.loginButtonVerticalSpace.priority=1000;
[self.view addConstraint:self.loginButtonVerticalSpace];
[self.view removeConstraint:consOld];
}
Thank you so much, guys....