试图使用CGContextAddArc ...没有绘制？ [英] Trying to use CGContextAddArc... nothing is drawn?

问题描述

我想画一个弧。

- (void)viewDidLoad {
    [super viewDidLoad];
    CGRect rect = CGRectMake(0,0,340,480);  
    UIView *ui = [[UIView alloc] initWithFrame:rect];
    [self.view addSubview:ui];
    CGContextRef context = UIGraphicsGetCurrentContext(); 
    CGContextAddArc(context, 50, 50, 20, 0, 30, 0); 
}

推荐答案

电弧在其可见之前。你在屏幕上有一个路径，但你必须笔画或填充之前绘制明显。

You have to stroke or fill the arc before its visible. You've got a path on screen but you have to stroke or fill it before draws visibly. Use these to do that..

//set the fill or stroke color
CGContextSetRGBFillColor(context, 0.5, 0.5, 0.5, 1.0);
CGContextSetRGBStrokeColor(context, 0.5, 0.5, 0.5, 1.0);

//fill or draw the path
CGContextDrawPath(context, kCGPathStroke);
CGContextDrawPath(context, kCGPathFill);

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