自动滚动 UIScrollView 以适应原生 iOS Mail.app 中的内容

Question

原生 iOS Mail.app 有一个很棒的创建新字母的功能。整个屏幕是UIScrollView，写信正文的地方是UITextView，滚动被禁用。

当您键入此TextView 的高度以及UIScrollView 的高度时，UIScrollView 会向下滚动，在键盘上方留下一些像素以显示新文本。

我知道这个过程必须在 textViewDidChange 方法中完成，但在尝试做同样的事情时，我的代码出现了问题 - UITextField 有时可能会在 UIScrollView 下关闭。这是我尝试这样做的方法：

-(void)textViewDidChange:(UITextView *)textView {

    CGRect frame = emailTextView.frame;
    frame.size.height = emailTextView.contentSize.height;
    emailTextView.frame = frame;
    mainScrollView.contentSize = CGSizeMake(320, emailTextView.contentSize.height + rightKeyboardSize.height + 20);

}

关于这里出了什么问题的任何想法？提前致谢！

Answer 1

好的，我实现了自己的示例项目来寻找答案。你应该替换你的名字。

首先，我将添加观察者来检测键盘何时显示或隐藏：

- (void)addKeyboardObserver
{
    // This could be in an init method.
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardDidShow:) name:UIKeyboardDidShowNotification object:nil];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(keyboardDidHide:) name:UIKeyboardDidHideNotification object:nil];
}

- (void)keyboardDidShow:(NSNotification*)notification
{
    NSDictionary* keyboardInfo = [notification userInfo];
    NSValue* keyboardFrameBegin = [keyboardInfo valueForKey:UIKeyboardFrameBeginUserInfoKey];
    _keyboardFrameBeginRect = [keyboardFrameBegin CGRectValue];
    UIScrollView *_scrollView = (UIScrollView*)self.view;
    _scrollView.frame = CGRectMake(_scrollView.frame.origin.x,
                                   _scrollView.frame.origin.y,
                                   _scrollView.frame.size.width,
                                   _scrollView.frame.size.height - _keyboardFrameBeginRect.size.height);
}

- (void)keyboardDidHide:(NSNotification*)notification
{
    UIScrollView *_scrollView = (UIScrollView*)self.view;
    _scrollView.frame = CGRectMake(_scrollView.frame.origin.x,
                                   _scrollView.frame.origin.y,
                                   _scrollView.frame.size.width,
                                   _scrollView.frame.size.height +
                               _keyboardFrameBeginRect.size.height);
}

然后，textViewDidChange: 方法改为：

- (void)textViewDidChange:(UITextView *)textView
{
    UIScrollView *_scrollView = (UIScrollView*)self.view;
    _textView.frame = CGRectMake(_textView.frame.origin.x,
                                 _textView.frame.origin.y,
                                 _textView.contentSize.width,
                                 _textView.contentSize.height);
    _scrollView.contentSize = _textView.frame.size;

    if (_scrollView.frame.size.height < _textView.frame.size.height) {
        CGPoint bottomOffset = CGPointMake(0,_textView.frame.size.height-_keyboardFrameBeginRect.size.height);
        [_scrollView setContentOffset:bottomOffset animated:NO];
    }
}

祝你好运！