UITextview 垂直居中
UITextView* content = (UITextView*) [cell viewWithTag:104];
[content addObserver:self forKeyPath:@"contentSize" options:(NSKeyValueObservingOptionNew) context:NULL];
#pragma mark - KVO
-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
UITextView *tv = object;
// Center vertical alignment
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};
}