稳健的解决方案应在以下情况下成立：
(1.) 显示属性字符串的文本视图
(2.) 通过点击键盘上的返回键创建一个新行
(3.) 通过键入溢出到下一行的文本创建的新行
(4.) 复制和粘贴文本
(5.)第一次点击返回键创建一个新行（参见 OP 中的 3 个步骤）
(6.) 设备旋转
(7.) 在某些情况下，我想不出你会...
为了在 iOS 7.1 中满足这些要求，似乎仍然需要手动滚动到插入符号。
当调用文本视图委托方法textViewDidChange:时，通常会看到手动滚动到插入符号的解决方案。但是，我发现这种技术不能满足上面的情况#5。即使在滚动到插入符号之前调用 tolayoutIfNeeded也无济于事。相反，我不得不滚动到CATransaction完成块内的插入符号：
// this seems to satisfy all of the requirements listed above–if you are targeting iOS 7.1
- (void)textViewDidChange:(UITextView *)textView
{
if ([textView.text hasSuffix:@"\n"]) {
[CATransaction setCompletionBlock:^{
[self scrollToCaretInTextView:textView animated:NO];
}];
} else {
[self scrollToCaretInTextView:textView animated:NO];
}
}
为什么这行得通？我不知道。你得问苹果工程师。
为了完整起见，这是与我的解决方案相关的所有代码：
#import "ViewController.h"
@interface ViewController () <UITextViewDelegate>
@property (weak, nonatomic) IBOutlet UITextView *textView; // full-screen
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
NSString *string = @"All work and no play makes Jack a dull boy.\n\nAll work and no play makes Jack a dull boy. All work and no play makes Jack a dull boy. All work and no play makes Jack a dull boy. All work and no play makes Jack a dull boy. All work and no play makes Jack a dull boy. All work and no play makes Jack a dull boy. All work and no play makes Jack a dull boy. All work and no play makes Jack a dull boy.";
NSAttributedString *attrString = [[NSAttributedString alloc] initWithString:string attributes:@{NSFontAttributeName: [UIFont fontWithName:@"Verdana" size:30.0]}];
self.textView.attributedText = attrString;
self.textView.delegate = self;
self.textView.backgroundColor = [UIColor yellowColor];
[self.textView becomeFirstResponder];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardIsUp:) name:UIKeyboardDidShowNotification object:nil];
}
// helper method
- (void)scrollToCaretInTextView:(UITextView *)textView animated:(BOOL)animated
{
CGRect rect = [textView caretRectForPosition:textView.selectedTextRange.end];
rect.size.height += textView.textContainerInset.bottom;
[textView scrollRectToVisible:rect animated:animated];
}
- (void)keyboardIsUp:(NSNotification *)notification
{
NSDictionary *info = [notification userInfo];
CGRect keyboardRect = [[info objectForKey:UIKeyboardFrameEndUserInfoKey] CGRectValue];
keyboardRect = [self.view convertRect:keyboardRect fromView:nil];
UIEdgeInsets inset = self.textView.contentInset;
inset.bottom = keyboardRect.size.height;
self.textView.contentInset = inset;
self.textView.scrollIndicatorInsets = inset;
[self scrollToCaretInTextView:self.textView animated:YES];
}
- (void)textViewDidChange:(UITextView *)textView
{
if ([textView.text hasSuffix:@"\n"]) {
[CATransaction setCompletionBlock:^{
[self scrollToCaretInTextView:textView animated:NO];
}];
} else {
[self scrollToCaretInTextView:textView animated:NO];
}
}
@end
如果您发现这不起作用的情况，请告诉我。
