白色背景上带有透明标题的 iOS UIButton

Question

我有一个带有透明背景和白色标题的自定义 UIButton。我正在寻找一种简单的解决方案来将其反转为突出显示(白色背景和透明标题)，因为它是在系统 UISegmentedControl 上实现的。

有没有比在用作 CALayer 掩码的快照上反转 alpha 更简单的解决方案？

如果不是，你能告诉我如何反转 CALayer alpha 吗？

Answer 1

您可以使用 Destination Out 作为混合模式在 CGContext 上绘制文本。

此代码似乎有效:

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor greenColor];

    UIFont* font = [UIFont fontWithName:@"Helvetica-Bold" size:18];
    NSString* buttonText = @"BUTTON";
    CGSize buttonSize =  CGSizeMake(200, 50);
    NSDictionary* textAttributes = @{NSFontAttributeName:font};

    CGSize textSize = [buttonText sizeWithAttributes:textAttributes];

    UIGraphicsBeginImageContextWithOptions(buttonSize, NO, [[UIScreen mainScreen] scale]);
    CGContextRef ctx = UIGraphicsGetCurrentContext();

    CGContextSetFillColorWithColor(ctx, [UIColor redColor].CGColor);

    UIBezierPath *path = [UIBezierPath bezierPathWithRect:CGRectMake(0, 0, buttonSize.width, buttonSize.height)];
    CGContextAddPath(ctx, path.CGPath);
    CGContextFillPath(ctx);

    CGContextSetBlendMode(ctx, kCGBlendModeDestinationOut);
    CGPoint center = CGPointMake(buttonSize.width/2-textSize.width/2, buttonSize.height/2-textSize.height/2);
    [@"BUTTON" drawAtPoint:center withAttributes:textAttributes];


    UIImage* viewImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    UIImageView* imgView = [[UIImageView alloc] initWithImage:viewImage];
    [self.view addSubview:imgView];
}

顺便说一句，如果你想在 UIButton 中设置 UIImage 而不是仅仅将它添加到 View 中:

UIButton* boton = [[UIButton alloc] initWithFrame:CGRectMake(50, 50, viewImage.size.width, viewImage.size.height)];
[boton setBackgroundColor:[UIColor clearColor]];
[boton setTitleColor:[UIColor redColor] forState:UIControlStateNormal];
boton.titleLabel.font = font;
[boton setTitle:buttonText forState:UIControlStateNormal];
[boton setImage:viewImage forState:UIControlStateHighlighted];
[self.view addSubview:boton];