如何设置带有动画和滚动位置的UITextView selectedTextRange [英] How can I set UITextView selectedTextRange with animation and scroll position

问题描述

我一直在尝试找到一种将光标设置在带有动画的长UITextView底部的方法。设置起来并不太困难，实际上这个答案很好地覆盖了它。 https://stackoverflow.com/a/34922332/563381

I've been trying to figure out a way to set the cursor to the bottom of a long UITextView with animation. Setting it wasn't too difficult, in fact this answer covers it very well. https://stackoverflow.com/a/34922332/563381

但是，对其进行动画处理并非易事。我找不到一个 setSelectedTextRange（animated：）。将其设置在 UIView.animate ... 块内似乎没有任何作用。我能想到的最好的方法是手动对滚动进行动画处理，然后在完成时设置 selectedTextRange 。但这很脆弱，通常看起来很杂乱，有时似乎根本不起作用。

However, animating it isn't so easy. There isn't a setSelectedTextRange(animated:) that I can find. Setting it inside a UIView.animate... block doesn't seem to do anything. The best I've been able to come up with is to animate the scroll manually then in the completion set the selectedTextRange. However this is fragile, often looks choppy, and seems on occasion to not work at all.

设置 selectedTextRange 它确实跳到了该位置。如果有一种方法可以避免这种跳跃，则动画可能会更流畅，并且至少不会那么脆弱，因为它不需要延迟，您可以使用 setContentOffset（animated）无需等待设置 selectedTextRange 。

When you set selectedTextRange it does jump to that location. If there was a way to avoid that jump the animation might be smoother and at least would be less fragile since it wouldn't require a delay and you could use setContentOffset(animated) without needing to wait to set the selectedTextRange.

另一种选择是找到一种导致 selectedTextRange 跳转为动画本身。在此方面，我尝试了在之前禁用滚动并在之后重新启用滚动的技巧，但这似乎对我不起作用。猜测在更高版本的iOS中已更改。

The other option is to find a way to cause the selectedTextRange jump to be animated itself. On this front I tried the trick of disabling scrolling before and reenabling after but that didn't seem to work for me. Guessing that has changed in later versions of iOS.

推荐答案

您可以使用setContentOffset（_，animation :)并检测结束动画并使用scrollViewDidEndScrollingAnimation并设置光标，如下所示：

You can use setContentOffset(_, animated:) and detect the end of the animation with scrollViewDidEndScrollingAnimation and set the cursor like so:

// The action to scroll down
@IBAction func test(_ sender: Any) {

    let offset = self.textView.contentSize.height - self.textView.frame.height
    self.textView.setContentOffset(CGPoint(x: 0, y: offset), animated: true)
}

// Setting the cursor down
func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {

    let offset = self.textView.contentSize.height - self.textView.frame.height

    if scrollView.contentOffset == CGPoint(x: 0, y: offset) {
        let newPosition = textView.endOfDocument
        self.textView.selectedTextRange = self.textView.textRange(from: newPosition, to: newPosition)
    }
}

您将需要将UITextViewDelegate添加到视图控制器并设置textView委托：

You will need to add UITextViewDelegate to your view controller and set the textView delegate:

textView.delegate = self

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