segmentView文字颜色渐变的方法

segment作为常用控件，在APP应用非常广泛，今天分享一个segment的title颜色渐变的方法，使应用具有更好的用户体验。

oldTitleView.textColor = [UIColor
                                  colorWithRed:[self.selectedColorRGBA[0] floatValue] + [self.deltaRGBA[0] floatValue] * progress
                                  green:[self.selectedColorRGBA[1] floatValue] + [self.deltaRGBA[1] floatValue] * progress
                                  blue:[self.selectedColorRGBA[2] floatValue] + [self.deltaRGBA[2] floatValue] * progress
                                  alpha:[self.selectedColorRGBA[3] floatValue] + [self.deltaRGBA[3] floatValue] * progress];
        
currentTitleView.textColor = [UIColor
                                      colorWithRed:[self.normalColorRGBA[0] floatValue] - [self.deltaRGBA[0] floatValue] * progress
                                      green:[self.normalColorRGBA[1] floatValue] - [self.deltaRGBA[1] floatValue] * progress
                                      blue:[self.normalColorRGBA[2] floatValue] - [self.deltaRGBA[2] floatValue] * progress
                                      alpha:[self.normalColorRGBA[3] floatValue] - [self.deltaRGBA[3] floatValue] * progress];
CGFloat deltaScale = self.titleBigScale - 1.0;
oldTitleView.currentTransformSx = self.titleBigScale - deltaScale * progress;
currentTitleView.currentTransformSx = 1.0 + deltaScale * progress;

其中titleBigScale为标题缩放倍数，可根据情况自行设定；process为滑动比例，通过以下方法计算：

    CGFloat tempProgress = scrollView.contentOffset.x / self.bounds.size.width;
    NSInteger tempIndex = tempProgress;
    CGFloat progress = tempProgress - floor(tempProgress);

其中颜色相关方法如下：

- (NSArray *)deltaRGBA {
    if (_deltaRGBA == nil) {
        NSArray *normalColorRgb = self.normalColorRGBA;
        NSArray *selectedColorRgb = self.selectedColorRGBA;
        
        NSArray *delta;
        if (normalColorRgb && selectedColorRgb) {
            CGFloat deltaR = [normalColorRgb[0] floatValue] - [selectedColorRgb[0] floatValue];
            CGFloat deltaG = [normalColorRgb[1] floatValue] - [selectedColorRgb[1] floatValue];
            CGFloat deltaB = [normalColorRgb[2] floatValue] - [selectedColorRgb[2] floatValue];
            CGFloat deltaA = [normalColorRgb[3] floatValue] - [selectedColorRgb[3] floatValue];
            delta = [NSArray arrayWithObjects:@(deltaR), @(deltaG), @(deltaB), @(deltaA), nil];
            _deltaRGBA = delta;
        }
    }
    return _deltaRGBA;
}

- (NSArray *)normalColorRGBA {
    if (!_normalColorRGBA) {
        NSArray *normalColorRGBA = [self getColorRGBA:self.segmentStyle.normalTitleColor];
        NSAssert(normalColorRGBA, @"设置普通状态的文字颜色时 请使用RGBA空间的颜色值");
        _normalColorRGBA = normalColorRGBA;
    }
    return  _normalColorRGBA;
}

- (NSArray *)selectedColorRGBA {
    if (!_selectedColorRGBA) {
        NSArray *selectedColorRGBA = [self getColorRGBA:self.segmentStyle.selectedTitleColor];
        NSAssert(selectedColorRGBA, @"设置选中状态的文字颜色时 请使用RGBA空间的颜色值");
        _selectedColorRGBA = selectedColorRGBA;
    }
    return  _selectedColorRGBA;
}

- (NSArray *)getColorRGBA:(UIColor *)color {
    CGFloat numOfcomponents = CGColorGetNumberOfComponents(color.CGColor);
    NSArray *rgbaComponents;
    if (numOfcomponents == 4) {
        const CGFloat *components = CGColorGetComponents(color.CGColor);
        rgbaComponents = [NSArray arrayWithObjects:@(components[0]), @(components[1]), @(components[2]), @(components[3]), nil];
    }
    return rgbaComponents; 
}

具体效果如下：