Get frame of a view after autolayout - ios

Question

I have a method:
- (void)underlineTextField:(UITextField *)tf {
CGFloat x = tf.frame.origin.x-8;
CGFloat y = tf.origin.y+tf.frame.size.height+1;
CGFloat width = self.inputView.frame.size.width-16;
UIView *line = [[UIView alloc] initWithFrame:(CGRect){x,y,width,1}];
line.backgroundColor = [UIColor whiteColor];
[self.inputView addSubview:line];
}
That underlines an input UITextField; The textfield has a width that changes depending on the screen width (nib autolayout).
I have tried using
[self.view setNeedsLayout];
[self.view layoutIfNeeded];
and
[self.inputView setNeedsLayout];
[self.inputView layoutIfNeeded];
before I call this method with no change in result. the resulting line is much wider than the UITextField (it matches the original size in the Nib).
I just want the resulting frame of the UITextField in question after being processed by the autolayout
SOLUTION: (using 'Masonry' Autolayout)
- (UIView *)underlineTextField:(UITextField *)tf {
UIView *line = [[UIView alloc] initWithFrame:CGRectZero];
line.backgroundColor = [UIColor whiteColor];
[self.inputView addSubview:line];
[line mas_makeConstraints:^(MASConstraintMaker *make) {
make.centerX.equalTo(tf.mas_centerX);
make.width.equalTo(tf.mas_width).with.offset(16);
make.height.equalTo(#1);
make.top.equalTo(tf.mas_bottom);
}];
return line;
}

Answer 1

Your underline view has a static frame, it is not connected to the textField through constraints. Instead of setting the frame, add constraints to self.inputView
- (void)underlineTextField:(UITextField *)tf {
UIView *line = [[UIView alloc] init];
line.backgroundColor = [UIColor whiteColor];
[line setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.inputView addSubview:line];
// Vertical constraints
[self.inputView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"V:[line(==1)]-(-1)-|" options:0 metrics:nil views:#{ #"line": line}]];
// Horizontal constraints
[self.inputView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:#"H:|-(-8)-[line]-8-|" options:0 metrics:nil views:#{ #"line": line}]];
[self.inputView layoutIfNeeded];
}
After the layoutIfNeeded call, the frame for your view should be right. I hoped I got the constants right. Because the line appears one unit under the textView make sure to unset Clip Subviews in the storyboard for the textField
I hope this works for you. Let me know if you have questions!

Answer 2

You could adjust the frame of the underline in viewDidLayoutSubviews which is called after auto layout has set all the frames.
Note that you're creating a new view and calling addSubview: each time. You should do that once when you create the text view, outside of this method. Otherwise you'll create a new UIView every time your user rotates the device.