设置 CGContext 透明背景 [英] Setting A CGContext Transparent Background
本文介绍了设置 CGContext 透明背景的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我仍在努力用 CGContext 画一条线.我实际上已经去画线了,但现在我需要 Rect 的背景是透明的,这样现有的背景就会显示出来.这是我的测试代码:
I am still struggling with drawing a line with CGContext. I have actually go to line to draw, but now I need the background of the Rect to be transparent so the existing background shows thru. Here's my test code:
(void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [UIColor clearColor].CGColor);
CGContextSetAlpha(context,0.0);
CGContextFillRect(context, rect);
CGContextSetStrokeColorWithColor(context, [UIColor whiteColor].CGColor);
CGContextSetLineWidth(context, 5.0);
CGContextMoveToPoint(context, 100.0,0.0);
CGContextAddLineToPoint(context,100.0, 100.0);
CGContextStrokePath(context);
}
有什么想法吗?
推荐答案
UIGraphicsGetCurrentContext()
之后调用 CGContextClearRect(context,rect)
好的,知道了.
带有该行的自定义视图应具有以下内容:
Your custom view with the line should have the following:
- (id)initWithFrame:(CGRect)frame {
if (self = [super initWithFrame:frame]) {
[self setBackgroundColor:[UIColor clearColor]];
}
return self;
}
- (void)drawRect:(CGRect)rect {
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextClearRect(context, rect);
CGContextSetStrokeColorWithColor(context, [UIColor whiteColor].CGColor);
CGContextSetLineWidth(context, 5.0);
CGContextMoveToPoint(context, 100.0,0.0);
CGContextAddLineToPoint(context,100.0, 100.0);
CGContextStrokePath(context);
}
我的测试使用它作为一个非常基本的 UIViewController:
My test used this as a very basic UIViewController:
- (void)viewDidLoad {
[super viewDidLoad];
UIImageView *v = [[UIImageView alloc] initWithFrame:self.view.bounds];
[v setBackgroundColor:[UIColor redColor]];
[self.view addSubview:v];
TopView *t = [[TopView alloc] initWithFrame:self.view.bounds];
[self.view addSubview:t];
[v release];
[t release];
}
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