屏蔽 uitextview/uiwebview 中的文本

Question

最后我选择花一些时间来寻找一种方法/实现 屏蔽 UITextView/UIWebView 中的文本。 现在我能做的是： - 添加一些自定义背景 - 添加带有一些文本的 uitextview/uiwebview - 添加一个 UIImageView（带有覆盖 png）或一个 CAGradientLayer 到 创建一个简单的蒙版效果 (*) 当然这不是灵丹妙药，至少还需要一颗 层（用 * 指出的那一层）。 此外，当你有一个完全透明的时候它不是那么好 背景 '因为每个人都可以识别出额外的视图/图层 淡出文字。 我搜索了整个谷歌，但仍然没有找到一个好的解决方案（我已经 发现关于屏蔽图像，等等等等）...... 有小费吗？ 提前致谢， 马西奥

PS 也许截图会更直接，给你！ http://grab.by/KzS

Answer 1

是的！我终于明白了。我不知道这是否是苹果的方式，但它确实有效。也许他们有机会使用一些私有 api。无论如何，这是一种关于我如何工作的伪算法：

1) 获取窗口截图

2) 使用 CGImageCreateWithImageInRect 裁剪所需的矩形

3) 应用渐变蒙版（从 Apple 的 Reflections 示例代码中窃取）

4) 使用新创建的图像创建一个 UIImageView

我还注意到，即使在最低的设备上，它也不会影响性能。 希望它会有所帮助！ 这是结果的一部分 (link text)

我已经向自己承诺实施一个类别只是为了让它变得更好。到目前为止，代码在不同的类中相当分散。 只是为了制作一个示例（仅支持横向，请参见下面的转换，仅支持顶部蒙版）。在这种情况下，我覆盖了需要屏蔽的表的 didMoveToWindow：

- (void)didMoveToWindow {
    if (self.window) {

        UIImageView *reflected = (UIImageView *)[self.superview viewWithTag:TABLE_SHADOW_TOP];
        if (!reflected) {
            UIImage *image = [UIImage screenshot:self.window];

            //
            CGRect croppedRect = CGRectMake(480-self.frame.size.height, self.frame.origin.x, 16, self.frame.size.width);
            CGImageRef cropImage = CGImageCreateWithImageInRect(image.CGImage, croppedRect);
            UIImage *reflectedImage = [UIImage imageMaskedWithGradient:cropImage];
            CGImageRelease(cropImage);

            UIImageView *reflected = [[UIImageView alloc] initWithImage:reflectedImage];
            reflected.transform = CGAffineTransformMakeRotation(-(M_PI/2));
            reflected.tag = TABLE_SHADOW_TOP;
            CGRect adjusted = reflected.frame;
            adjusted.origin = self.frame.origin;
            reflected.frame = adjusted;
            [self.superview addSubview:reflected];
            [reflected release];
        }
    }
}

这是 uiimage 类别：

CGImageRef CreateGradientImage(int pixelsWide, int pixelsHigh)
{
    CGImageRef theCGImage = NULL;

    // gradient is always black-white and the mask must be in the gray colorspace
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();

    // create the bitmap context
    CGContextRef gradientBitmapContext = CGBitmapContextCreate(NULL, pixelsWide, pixelsHigh,
                                                               8, 0, colorSpace, kCGImageAlphaNone);

    // define the start and end grayscale values (with the alpha, even though
    // our bitmap context doesn't support alpha the gradient requires it)
    CGFloat colors[] = {0.0, 1.0, 1.0, 1.0};

    // create the CGGradient and then release the gray color space
    CGGradientRef grayScaleGradient = CGGradientCreateWithColorComponents(colorSpace, colors, NULL, 2);
    CGColorSpaceRelease(colorSpace);

    // create the start and end points for the gradient vector (straight down)
    CGPoint gradientStartPoint = CGPointZero;
    //  CGPoint gradientStartPoint = CGPointMake(0, pixelsHigh);
    CGPoint gradientEndPoint = CGPointMake(pixelsWide/1.75, 0);

    // draw the gradient into the gray bitmap context
    CGContextDrawLinearGradient(gradientBitmapContext, grayScaleGradient, gradientStartPoint,
                                gradientEndPoint, kCGGradientDrawsAfterEndLocation);
    CGGradientRelease(grayScaleGradient);

    // convert the context into a CGImageRef and release the context
    theCGImage = CGBitmapContextCreateImage(gradientBitmapContext);
    CGContextRelease(gradientBitmapContext);

    // return the imageref containing the gradient
    return theCGImage;
}

CGContextRef MyCreateBitmapContext(int pixelsWide, int pixelsHigh)
{
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // create the bitmap context
    CGContextRef bitmapContext = CGBitmapContextCreate (NULL, pixelsWide, pixelsHigh, 8,
                                                        0, colorSpace,
                                                        // this will give us an optimal BGRA format for the device:
                                                        (kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst));
    CGColorSpaceRelease(colorSpace);

    return bitmapContext;
}

+ (UIImage *)imageMaskedWithGradient:(CGImageRef)image {

    UIDeviceOrientation deviceOrientation = [UIDevice currentDevice].orientation;
    DEBUG(@"need to support deviceOrientation: %i", deviceOrientation);

    float width  = CGImageGetWidth(image);
    float height = CGImageGetHeight(image);

    // create a bitmap graphics context the size of the image
    CGContextRef mainViewContentContext = MyCreateBitmapContext(width, height);

    // create a 2 bit CGImage containing a gradient that will be used for masking the 
    // main view content to create the 'fade' of the reflection.  The CGImageCreateWithMask
    // function will stretch the bitmap image as required, so we can create a 1 pixel wide gradient
    CGImageRef gradientMaskImage = CreateGradientImage(width, 1);

    // create an image by masking the bitmap of the mainView content with the gradient view
    // then release the  pre-masked content bitmap and the gradient bitmap
    CGContextClipToMask(mainViewContentContext, CGRectMake(0.0, 0.0, width, height), gradientMaskImage);
    CGImageRelease(gradientMaskImage);

    // draw the image into the bitmap context
    CGContextDrawImage(mainViewContentContext, CGRectMake(0, 0, width, height), image);

    // create CGImageRef of the main view bitmap content, and then release that bitmap context
    CGImageRef reflectionImage = CGBitmapContextCreateImage(mainViewContentContext);
    CGContextRelease(mainViewContentContext);

    // convert the finished reflection image to a UIImage 
    UIImage *theImage = [UIImage imageWithCGImage:reflectionImage];

    // image is retained by the property setting above, so we can release the original
    CGImageRelease(reflectionImage);

    return theImage;

}

希望对你有帮助。