如何按时间间隔逐字母更改标签文本颜色？

Question

我尝试了以下代码：

[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(myTimerMethod:) userInfo:nil repeats:NO];

-(void)myTimerMethod:(NSTimer*)timer
{

    label.textColor = [UIColor colorWithRed:0.5 green:0.5 blue:0.22 alpha:1.0];

}

但我希望下面的图片类型改变颜色。

Answer 1

UILabel现在支持属性字符串。所以你可以做类似于以下的事情

int lengthOfTextToColor = 0;
NSMutableAttributedString *textString = [[NSMutableAttributedString alloc] initWithString:@"I think you are making a karaoke app"];

-(void)colorChangeTimer:(NSTimer *)timer {
    lengthOfTextToColor ++;
    NSRange range = NSMakeRange(0, lengthOfTextToColor);
    NSDictionary *colorAttribute = @{NSForegroundColorAttributeName:[UIColor blueColor]};
    [textString setAttributes: colorAttribute range:range];
    self.label.attributedText = textString;
}

但是归因于字符串有其局限性。 如果您希望实现真正精美的文本，请拔出袜子并检查Text Programming Guide和CoreText Framework。你可以找到很多tutorials for Core Text

Answer 2

您必须使用NSMutableAttributedString：

_string = [[NSMutableAttributedString alloc] initWithString:@"your string"];
_index = 0;
[NSTimer scheduledTimerWithInterval:1.0 target:self selector:@selector(yourSelector) userInfo:nil repeats:NO];

- (void)yourSelector {
    [_string setAttributes:@{NSForegroundColorAttributeName: [UIColor colorWithRed:0 green:0 blue:0 alpha:1]} range:NSMakeRange(_index, 1)];
    [label setAttributedText:_string];
    _index++;
}