how to fix width in UIButton's sizeToFit/sizeThatFit?

I found the sizeToFit or sizeThatFits will change UIButton 's current width.

UIButton* btn = [UIButton buttonWithType:UIButtonTypeCustom];
btn.frame = CGRectMake(100, 100, 200, 40);
btn.backgroundColor = [UIColor redColor];
[btn.titleLabel setText:@"ssdkfjsakdfjsakfjaksdjfkasjfkasjkfasjkfsajfkasjkas"];
btn.titleLabel.numberOfLines = 0;
[btn setTitle:@"ssdkfjsakdfjsakfjaksdjfkasjfkasjkfasjkfsajfkasjkas" forState:UIControlStateNormal];
[self.view addSubview:btn];

NSLog(@"before sizeToFit: %@",NSStringFromCGRect(btn.frame));
CGSize size = [btn sizeThatFits:CGSizeMake(200, 1000)];
[btn sizeToFit];

NSLog(@"after sizeToFit:%@",NSStringFromCGRect(btn.frame));
NSLog(@" sizeThatFits:%@",NSStringFromCGSize(size));

and the output will be:

before sizeToFit: {{100, 100}, {200, 40}}
after sizeToFit:{{100, 100}, {392, 34}}
sizeThatFits:{392, 34}

this is not the behavior I want , if I want the sizeToFit resizing the button frame to its proper height based on its origin width. how to achive this?

If you want to change the size set by sizeToFit, you need to override the sizeThatFits method. Create a subclass of UIButton as follows:

Swift:

class MyButton: UIButton {
    override func sizeThatFits(_ size: CGSize) -> CGSize {
        let sizeThatFits = super.sizeThatFits(size)
        return CGSize(width: sizeThatFits.width, height: self.frame.height)
    }
}

Objective C:

@implementation MyButton

- (CGSize)sizeThatFits:(CGSize)size {
    CGSize sizeThatFits = [super sizeThatFits:size];
    return CGSizeMake(sizeThatFits.width, self.frame.size.height);
}

@end

And use the subclassed button instead of UIButton.

UIButton* btn = [MyButton buttonWithType:UIButtonTypeCustom];

Reference: Apple Doc: sizeToFit