如何在UIView下绘制阴影？ [英] How do I draw a shadow under a UIView?

问题描述

我想在Cocoa Touch中的 UIView 底部画一个阴影。我理解我应该使用 CGContextSetShadow（）来绘制阴影，但Quartz 2D编程指南有点含糊：

I'm trying to draw a shadow under the bottom edge of a UIView in Cocoa Touch. I understand that I should use CGContextSetShadow() to draw the shadow, but the Quartz 2D programming guide is a little vague:

1. 保存图形状态。


2. 调用函数 CGContextSetShadow ，传递相应的值。 / li>
   
3. 执行要应用阴影的所有绘图。


4. 恢复图形状态

1. Save the graphics state.
2. Call the function CGContextSetShadow, passing the appropriate values.
3. Perform all the drawing to which you want to apply shadows.
4. Restore the graphics state

我在 UIView 子类中尝试了以下操作：

I've tried the following in a UIView subclass:

- (void)drawRect:(CGRect)rect {
    CGContextRef currentContext = UIGraphicsGetCurrentContext();
    CGContextSaveGState(currentContext);
    CGContextSetShadow(currentContext, CGSizeMake(-15, 20), 5);
    CGContextRestoreGState(currentContext);
    [super drawRect: rect];
}

..但这对我不起作用，我有点（b）如果我需要对我的 UIView 做任何事情，以使这项工作？

..but this doesn't work for me and I'm a bit stuck about (a) where to go next and (b) if there's anything I need to do to my UIView to make this work?

推荐答案

在当前代码中，保存当前上下文的 GState ，配置它来绘制阴影。 。并将其还原到它是在配置它绘制阴影之前。然后，最后，你调用超类的实现 drawRect ：

In your current code, you save the GState of the current context, configure it to draw a shadow .. and the restore it to what it was before you configured it to draw a shadow. Then, finally, you invoke the superclass's implementation of drawRect: .

任何应该受阴影影响的图形设置需要在之后

Any drawing that should be affected by the shadow setting needs to happen after

CGContextSetShadow(currentContext, CGSizeMake(-15, 20), 5);

但之前

CGContextRestoreGState(currentContext);

<

So if you want the superclass's drawRect: to be 'wrapped' in a shadow, then how about if you rearrange your code like this?

- (void)drawRect:(CGRect)rect {
    CGContextRef currentContext = UIGraphicsGetCurrentContext();
    CGContextSaveGState(currentContext);
    CGContextSetShadow(currentContext, CGSizeMake(-15, 20), 5);
    [super drawRect: rect];
    CGContextRestoreGState(currentContext);
}

这篇关于如何在UIView下绘制阴影？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！