在UITextView中垂直居中文本 [英] Center text vertically in a UITextView

问题描述

我希望将文本垂直置于一个填满整个屏幕的大 UITextView 中 - 这样当文字很少时，请说几个字，它以身高为中心。
这不是关于文本居中（可以在IB中找到的属性）的问题，而是关于将文本垂直放在 UITextView 如果文本很短，那么 UITextView 中没有空白区域。
可以这样做吗？提前致谢！

I want to center the text vertically inside a big UITextView that fills the whole screen - so that when there's little of text, say a couple of words, it is centered by height. It's not a question about centering the text (a property that can be found in IB) but about putting the text vertically right in the middle of UITextView if the text is short, so there are no blank areas in the UITextView. Can this be done? Thanks in advance!

推荐答案

首先为 contentSize 键添加一个观察者加载视图时 UITextView 的值：

First add an observer for the contentSize key value of the UITextView when the view is loaded:

- (void) viewDidLoad {
     [textField addObserver:self forKeyPath:@"contentSize" options:(NSKeyValueObservingOptionNew) context:NULL];
     [super viewDidLoad];
}

然后添加此方法以调整 contentOffset 每次 contentSize 值更改时：

Then add this method to adjust the contentOffset every time the contentSize value changes:

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
     UITextView *tv = object;
     CGFloat topCorrect = ([tv bounds].size.height - [tv contentSize].height * [tv zoomScale])/2.0;
     topCorrect = ( topCorrect < 0.0 ? 0.0 : topCorrect );
     tv.contentOffset = (CGPoint){.x = 0, .y = -topCorrect};
}

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