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

问题描述

我正在尝试在 Cocoa Touch 中的 UIView 的底部边缘下绘制阴影.我知道我应该使用 CGContextSetShadow() 来绘制阴影，但是 Quartz 2D 编程指南有点模糊:

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，传递适当的值.
3. 执行要应用阴影的所有绘图.
4. 恢复图形状态

我在 UIView 子类中尝试了以下内容:

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，我对 (a) 下一步要去哪里以及 (b) 是否需要对我的 UIView 做任何事情使这项工作?

..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

在你当前的代码中，你保存当前上下文的GState，配置它来绘制一个阴影..并恢复它到您将其配置为绘制阴影之前的状态.然后，最后，您调用超类的 drawRect 实现: .

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: .

任何应该受阴影设置影响的绘图都需要在之后

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);

因此，如果您希望超类的 drawRect: 被包裹"在阴影中，那么如果您像这样重新排列代码呢?

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);
}

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