UIView子类绘制背景尽管完全空drawRect： - 为什么？ [英] UIView subclass draws background despite completely empty drawRect: - why?

问题描述

所以，我有一个自定义的UIView子类，使绘制圆角边缘。事情绘制完美，但背景总是填充整个边界，尽管剪切到一个路径第一。边框也会在矩形背景上方绘制 ，尽管我在drawRect：前绘制边框。所以我删除了drawRect：的整个内容，现在几乎是空的 - 但是背景被绘制了！

So, I have a custom UIView subclass which enables drawing of rounded edges. The thing draws perfectly, however the background always fills the whole bounds, despite clipping to a path first. The border also draws above the rectangular background, despite the fact that I draw the border in drawRect: before the background. So I removed the whole content of drawRect:, which is now virtually empty - nevertheless the background gets drawn!

任何人都有解释？我在Interface Builder中设置了backgroundColor。谢谢！

Anybody an explanation for this? I set the backgroundColor in Interface Builder. Thanks!

推荐答案

很抱歉这个独白。 ：）

Sorry for this monologue. :)

事情是，UIView的图层显然绘制了背景，它独立于 drawRect：。这就是为什么你不能通过重写 drawRect：来删除背景。

The thing is that the UIView's layer apparently draws the background, which is independent from drawRect:. This is why you can't get rid of the background by overriding drawRect:.

code> - （void）drawLayer：（CALayer *）layer inContext：（CGContextRef）ctx 并使图层绘制任何你想要的，或者你覆盖 - ）setBackgroundColor：（UIColor *）newColor ，并且不要将 newColor 指定给 backgroundColor ，而是指定给自己的ivar，如 myBackgroundColor 。然后，您可以在drawRect中使用 myBackgroundColor ;

You can either override - (void)drawLayer:(CALayer *)layer inContext:(CGContextRef)ctx and make the layer draw whatever you want, or you override - (void) setBackgroundColor:(UIColor *)newColor and don't assign newColor to backgroundColor, but to your own ivar, like myBackgroundColor. You can then use myBackgroundColor in drawRect; to draw the background however you like.

覆盖 setBackgroundColor：

定义一个背景颜色的实例变量，例如 myBackgroundColor 。在你的init方法中，设置真实的背景颜色为clearColor：

Define an instance variable to hold your background color, e.g. myBackgroundColor. In your init methods, set the real background color to be the clearColor:

- (id) initWithCoder:(NSCoder *)aDecoder
{
    if ((self = [super init...])) {
        [super setBackgroundColor:[UIColor clearColor]];
    }
    return self;
}

覆盖：

- (void) setBackgroundColor:(UIColor *)newColor
{
    if (newColor != myBackgroundColor) {
        [myBackgroundColor release];
        myBackgroundColor = [newColor retain];
    }
}

然后使用 myBackgroundColor 你的drawRect：方法。这样，您可以使用代码中从Interface Builder（或Xcode4）分配的颜色。

Then use myBackgroundColor in your drawRect: method. This way you can use the color assigned from Interface Builder (or Xcode4) in your code.

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