Question

尝试在UITextView中慢慢显示类似旧电传的文本。工作得很好，直到滚动视图，此时它应该是一行一行的向上滚动。但只是颤抖，并在一个班次上升。下面的代码段，不确定UI刷新和计时器是否有问题？

- (void) refreshLocationDescriptionWith: (NSArray *) inMessageList
{
    //
    // Refresh the location textview by appending new array of string messages
    //

    // Trim old description by half to prevent it growing too long
    //
    int const kMaxTextSize = 2000;
    NSString *oldDescription;
    if ([dispLocationDetails.text length] > kMaxTextSize)
    {
        NSString *trimDescription   = [dispLocationDetails.text substringFromIndex: kMaxTextSize / 2];
        oldDescription              = [NSString stringWithFormat: @"....... %@", trimDescription];
    }
    else
        oldDescription = dispLocationDetails.text;

    // Disable keyboard entry whilst displaying
    [self disableKeyBoardEntry];    

    // Go through all messages and display 'slowly'
    //

    NSTimeInterval nextDelay = 0;
    NSTimeInterval stepDelay = 0.03;

    for (NSString *nextMessage in inMessageList)
    {
        // Add to existing text display with one character at a time, with delay to 'scroll' text
        for (NSRange stringRange = NSMakeRange(0, 1); stringRange.location < [nextMessage length]; stringRange.location += 1)
        {
            NSString *nextChar = [nextMessage substringWithRange: stringRange];            
            [self performSelector: @selector(addCharToLocationDisplay:) withObject: nextChar afterDelay: nextDelay];            
            nextDelay += stepDelay;
        }

        [self performSelector: @selector(addCharToLocationDisplay:) withObject: @"\n" afterDelay: nextDelay];
    }

    [self performSelector: @selector(addCharToLocationDisplay:) withObject: @"\n" afterDelay: nextDelay];

    // Re-enable keyboard entry
    [self performSelector: @selector(enableKeyBoardEntry) withObject: nil afterDelay: nextDelay];

}

- (void) addCharToLocationDisplay: (NSString *) nextChar
{
    //
    // Add one char at a time to the text view display
    //

    NSString *newText                = [NSString stringWithFormat: @"%@%@", dispLocationDetails.text, nextChar];
    self.dispLocationDetails.text    = newText;

    NSRange range = NSMakeRange(dispLocationDetails.text.length - 1, 1);
    [dispLocationDetails scrollRangeToVisible:range];
}

Answer 1

使用块动画

完成

// Scroll through text, one char at a time with delay to simulate teletype type display
//
NSTimeInterval nextDelay = 0;
NSTimeInterval stepDelay = 0.03;

if (dispLocationDetails.text.length > 0)
    [self performSelector: @selector(addCharToLocationDisplay:) withObject: @"\n" afterDelay: nextDelay];

for (NSString *nextMessage in inMessageList)
{
    for (NSRange stringRange = NSMakeRange(0, 1); stringRange.location < [nextMessage length]; stringRange.location += 1)
    {
        NSString *nextChar = [nextMessage substringWithRange: stringRange];            
        [self performSelector: @selector(addCharToLocationDisplay:) withObject: nextChar afterDelay: nextDelay];            
        nextDelay += stepDelay;
    }

    [self performSelector: @selector(addCharToLocationDisplay:) withObject: @"\n" afterDelay: nextDelay];
}

和

- (void) addCharToLocationDisplay: (NSString *) nextChar
{
    //
    // Add one char at a time to the text view display
    // Scroll up line by line as text displayed
    //

    NSString *newText                = [NSString stringWithFormat: @"%@%@", dispLocationDetails.text, nextChar];
    self.dispLocationDetails.text    = newText;

    [UIView animateWithDuration:.25 animations:^
     {
         CGPoint bottomOffset = CGPointMake(0, dispLocationDetails.contentSize.height - dispLocationDetails.bounds.size.height);
         DLog(@"Bottom: %f", bottomOffset.y);
         if (bottomOffset.y > 0)
             [self.dispLocationDetails setContentOffset: bottomOffset animated: NO];
     }];
}

在UITextView中滚动电传文本显示不滚动

1 个答案: