UITextView setContentOffset：layoutSubviews中的CGPointZero在iOS8中不起作用

Question

I have a PopupView that extends UIView . In PopupView I have a UITextView .
When the PopupView show, my UITextView doesn't start at first line (it scroll a little bit to bottom)
So I use the code below to scroll the UITextView to top after PopupView appears

- (void)layoutSubviews{
    [super layoutSubviews];

    [self.contentTextView setContentOffset:CGPointZero animated:NO];
}

It works well in iOS9 (both device and simulator) but it doesn't work in iOS8
Any idea to fix it. Any help would be great appreciated

UPDATE

I found that drawRect get called after layoutSubviews and if I setContentOffset:CGPointZero inside it, it will work

-(void)drawRect:(CGRect)rect{
    [self.contentTextView setContentOffset:CGPointZero];
}

But I found the purpose of drawRect :

drawRect: - Implement this method if your view draws custom content. If your view does not do any custom drawing, avoid overriding this method.

Is it good to use drawRect without layoutSubviews in my case?

Answer 1

According to @longpham instruction, the drawRect() will use GPU so it's not good. Here is the solution that solve my problem

-(void)awakeFromNib{
    [super awakeFromNib];
    [self layoutIfNeeded]; // call layoutIfNeeded here to make layoutSubviews get called whenever layout change
}
- (void)layoutSubviews{
    ...
    [self.contentTextView setContentOffset:CGPointZero];
}

Answer 2

it worked for me

- (void)drawRect:(CGRect)rect {

    self.textView=[[UITextView alloc] initWithFrame:CGRectMake(0, 0, self.frame.size.width, self.frame.size.height)];

    [self addSubview:self.textView];

}