I have a UITextField with custom keyboard, basically like a calculator. I would like my keyboard show up by default, so i used [self.topInputTextField becomeFirstResponder]; in viewDidLoad, I think that's very common usage. However, it causes some very weird actions on my textfield.
When i set my textfield as the first responder in viewDidLoad, and every time after i done editing, the text will jump, and when i click another text field and and click the first text field again, the texts in the first text field sometimes shift down and disappear, but sometimes not. I feel it's very hard to describe, so i recorded a GIF image for it.
And the reason, that I am sure [self.topInputTextField becomeFirstResponder]; causing the issue, is when i comment that line of code out, everything back to normal. here is the GIF after i comment out that line:
that's vert strange to me, between 2 GIF file, the only change i did is comment out that line of code. I couldn't find any solution on SE. Any idea would be very appreciated.
Edit: One more thing is I tried to change font, and font sizes, they all have similar strange behaviors.
*Edit 2:** here is how i set up my textfield,i didn't do anything fancy
Try calling the keyboard in viewDidAppear, this method gets called after viewDidLoad. I assume it's because you should only call the keyboard on a loaded view that has appeared to the user, so if you call it before the view actually appears it will cause unexpected behaviour.
viewDidLoad is too early for calling this, the UI hasn't worked out which size your screen is, or even which orientation your device is in. It isn't yet a UI really... Try it in willAppearAnimated: ..
来源：https://stackoverflow.com/questions/21899851/when-set-uitextfield-as-firstresponder-programmatically-cause-some-weird-action