如何使UIImageView变暗 [英] how to darken a UIImageView

问题描述

我需要在触摸UIImageView时使其变暗，几乎与跳板(主屏幕)上的图标一样， .

I need to darken a UIImageView when it gets touched, almost exactly like icons on the springboard (home screen).

应该为我添加具有0.5 alpha和黑色背景的UIView.这看起来很笨拙.我应该使用图层还是其他东西(CALayers).

Should I be added UIView with a 0.5 alpha and black background. This seems clumsy. Should I be using Layers or something (CALayers).

推荐答案

如何对UIView进行子类化并添加UIImage ivar(称为image)?然后，您可以覆盖-drawRect:类似这样的内容，只要您在触摸时设置了一个名为被按下的布尔ivar即可.

How about subclassing UIView and adding a UIImage ivar (called image)? Then you could override -drawRect: something like this, provided you had a boolean ivar called pressed that was set while touched.

- (void)drawRect:(CGRect)rect
{
[image drawAtPoint:(CGPointMake(0.0, 0.0))];

// if pressed, fill rect with dark translucent color
if (pressed)
    {
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextSaveGState(ctx);
    CGContextSetRGBFillColor(ctx, 0.5, 0.5, 0.5, 0.5);
    CGContextFillRect(ctx, rect);
    CGContextRestoreGState(ctx);
    }
}

您可能要尝试使用上面的RGBA值.而且，当然，非矩形形状需要做更多的工作-例如CGMutablePathRef.

You would want to experiment with RGBA values above. And, of course, non-rectangular shapes would require a bit more work - like a CGMutablePathRef.

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