如何将UIScrollView滚动到UITextView的光标位置？

Question

我有一个类似于笔记应用程序的视图 - 即在一张带衬里的纸上打字.为了使文本和纸张同时滚动,我已经禁用了UITextView的滚动,而是将我的UITextView和我的UIImageView放在UIScrollView中.

唯一的问题是,当用户键入时,文本消失在键盘下方,因为显然UIScrollView不知道滚动到光标位置.

有没有简单的方法可以检索光标位置并告诉UIScrollView在那里滚动？

- -编辑 - -

从这里类似的东西开始(有人试图用UITableView做类似的事情),我已经设法制作了一个不断增长的,可编辑的UITextView,它具有几乎完全滚动的固定背景.现在唯一的问题是:

1. 如果用户输入速度特别快,文本会向上移动,这会有轻微的颤抖.
2. 如果用户隐藏键盘,选择屏幕底部的文本,然后再次显示键盘,他们必须在文本再次可见之前键入几个字母 - 它不会立即向上滚动.
3. 当用户隐藏键盘时,动画作为滚动视图的框架填满屏幕感觉不太合适.

这是代码 - 如果有人能进一步完善它,我将非常感激...

#import "NoteEditViewController.h"
#import "RLWideLabelTableCell.h"

@implementation NoteEditViewController
@synthesize keyboardSize;
@synthesize keyboardHideDuration;
@synthesize scrollView;
@synthesize noteTextView;

//
// Dealloc and all that stuff
//
- (void)loadView
{
    [super loadView];
    UIScrollView *aScrollView = [[UIScrollView alloc] initWithFrame:self.view.bounds];
    self.scrollView = aScrollView; [aScrollView release];
    self.scrollView.contentSize = CGSizeMake(self.view.frame.size.width, noteTextView.frame.size.height);
    [self.view addSubview:scrollView];
}

- (void)viewDidLoad
{   
    [super viewDidLoad];

    // Get notified when keyboard is shown. Don't need notification when hidden because we are
    // using textViewDidEndEditing so we can start animating before the keyboard disappears.
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(keyboardWasShown:)
                                                 name:UIKeyboardDidShowNotification object:nil];

    // Add the Done button so we can test dismissal of the keyboard    
    UIBarButtonItem *doneButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone 
        target:self
        action:@selector(doneButton:)];
    self.navigationItem.rightBarButtonItem = doneButton; [doneButton release];

    // Add the background image that will scroll with the text
    CGRect noteImageFrame = CGRectMake(self.view.bounds.origin.x, 
                                       noteTitleImageFrame.size.height, 
                                       self.view.bounds.size.width, 500);    

    UIView *backgroundPattern = [[UIView alloc] initWithFrame:noteImageFrame];
    backgroundPattern.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"Notepaper-iPhone-Line"]];
    [self.scrollView addSubview:backgroundPattern];
    [self.view sendSubviewToBack:backgroundPattern];
    [backgroundPattern release];

    // Add the textView
    CGRect textViewFrame = CGRectMake(noteImageFrame.origin.x+27, 
                                      noteImageFrame.origin.y-3, 
                                      noteImageFrame.size.width-35,
                                      noteImageFrame.size.height);

    RLTextView *textView = [[RLTextView alloc] initWithFrame:textViewFrame];
    self.noteTextView = textView; [textView release];
    self.noteTextView.font = [UIFont fontWithName:@"Cochin" size:21];
    self.noteTextView.backgroundColor = [UIColor clearColor];
    self.noteTextView.delegate = self;
    self.noteTextView.scrollEnabled = NO;
    [self.scrollView addSubview:self.noteTextView];
}

- (void)doneButton:(id)sender
{
    [self.view endEditing:TRUE];
}

// When the keyboard is shown, the UIScrollView's frame shrinks so that it fits in the
// remaining space
- (void)keyboardWasShown:(NSNotification*)aNotification
{
    NSDictionary* info = [aNotification userInfo];
    CGSize kbSize = [[info objectForKey:UIKeyboardFrameBeginUserInfoKey] CGRectValue].size;
    float kbHideDuration = [[info objectForKey:UIKeyboardAnimationDurationUserInfoKey] floatValue];
    self.keyboardHideDuration = kbHideDuration;
    self.keyboardSize = kbSize;
    self.scrollView.frame = CGRectMake(self.view.bounds.origin.x, 
                                       self.view.bounds.origin.y, 
                                       self.view.bounds.size.width, 
                                       self.view.bounds.size.height - kbSize.height);    
}

// When the user presses 'done' the UIScrollView expands to the size of its superview
// again, as the keyboard disappears.
- (void)textViewDidEndEditing:(UITextView *)textView
{
    [UIScrollView animateWithDuration:keyboardHideDuration animations:^{self.scrollView.frame = self.view.bounds;}];
}

// This method needs to get called whenever there is a change of cursor position in the text box
// That means both textViewDidChange: and textViewDidChangeSelection:
- (void)scrollToCursor
{
    // if there is a selection cursor…
    if(noteTextView.selectedRange.location != NSNotFound) {
        NSLog(@"selectedRange: %d %d", noteTextView.selectedRange.location, noteTextView.selectedRange.length);

        // work out how big the text view would be if the text only went up to the cursor
        NSRange range;
        range.location = noteTextView.selectedRange.location;
        range.length = noteTextView.text.length - range.location;
        NSString *string = [noteTextView.text stringByReplacingCharactersInRange:range withString:@""];
        CGSize size = [string sizeWithFont:noteTextView.font constrainedToSize:noteTextView.bounds.size lineBreakMode:UILineBreakModeWordWrap];

        // work out where that position would be relative to the textView's frame
        CGRect viewRect = noteTextView.frame;  
        int scrollHeight = viewRect.origin.y + size.height;
        CGRect finalRect = CGRectMake(1, scrollHeight, 1, 1);

        // scroll to it
        [self.scrollView scrollRectToVisible:finalRect animated:YES];
    }
}

// Whenever the text changes, the textView's size is updated (so it grows as more text
// is added), and it also scrolls to the cursor.
- (void)textViewDidChange:(UITextView *)textView
{
    noteTextView.frame = CGRectMake(noteTextView.frame.origin.x, 
                                    noteTextView.frame.origin.y, 
                                    noteTextView.frame.size.width, 
                                    noteTextView.contentSize.height);
    self.scrollView.contentSize = CGSizeMake(self.scrollView.contentSize.width, 
                                             noteTextView.frame.size.height+200);
    [self scrollToCursor];
}

// The textView scrolls to the cursor whenever the user changes the selection point.
- (void)textViewDidChangeSelection:(UITextView *)aTextView 
{
    [self scrollToCursor];
}

// PROBLEM - the textView does not scroll until the user starts typing - just selecting
// it is not enough. 
- (void)textViewDidBeginEditing:(UITextView *)textView
{
    [self scrollToCursor];
}

Answer 1

很酷,你发现我的帖子,很高兴它有用!

我相信你可能不会因为这条线而看到底线:

CGRect finalRect = CGRectMake(1, scrollHeight, 1, 1);

您正在创建一个1x1点框.单行文本可能是20或30点高(取决于字体大小).因此,如果您将此点滚动到可见,它可能只显示底线的最顶部像素 - 使底线有效隐形!如果你使finalRect更高一点,它覆盖整行,它可能会更好:

CGRect finalRect = CGRectMake(1, scrollHeight, 1, 30);

此外,您可能会多次调用scrollRectToVisible代码,这可能会导致"颤抖".在我的代码中,我只从textViewDidChangeSelection运行scrollRectToVisible,并在textViewDidChange中调整UITextView(如果需要).UIScrollView(以及继承UITableView)具有内置支持,可以将主动选择的元素滚动显示,在我的测试中,只需在键入时调整UITextView的大小(但在通过触摸选择特定点时不行).