iphone - UIGraphicsBeginImageContext 未绘制

Question

我想经常在我的 View 中画线，但它不起作用。我不想使用drawRect，因为我还必须维护之前绘制的线的状态。下面是画线的代码。请指导。

- (void)drawPathWithPoints:(int)xAxis andYaxis:(int)yAxis
{    
    CGSize screenSize = drawingImgView.frame.size;

    UIGraphicsBeginImageContext(drawingImgView.frame.size);

    CGContextRef currentContext = UIGraphicsGetCurrentContext();
     [drawingImgView.image drawInRect:CGRectMake(0, 0, screenSize.width, screenSize.height)];

    CGContextSetLineCap(currentContext, kCGLineCapRound);
    CGContextSetLineWidth(currentContext, 9.0);
    CGContextSetRGBStrokeColor(currentContext, 0, 0, 1, 1);
    CGContextBeginPath(currentContext);

    CGMutablePathRef pointPath = CGPathCreateMutable();

    CGContextMoveToPoint(currentContext,xAxis,yAxis);

    CAKeyframeAnimation *pathAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    pathAnimation.duration = 3.0;
    pathAnimation.delegate = self;
    pathAnimation.calculationMode = kCAAnimationPaced;
    pathAnimation.fillMode = kCAFillModeForwards;
    pathAnimation.removedOnCompletion = NO;

    CGPathMoveToPoint(pointPath, NULL, xAxis, yAxis);
    CGContextAddLineToPoint(currentContext, xAxis, yAxis);
    CGPathAddLineToPoint(pointPath, NULL, xAxis, yAxis);

    pathAnimation.path = pointPath;

    myLayer = [[CAShapeLayer alloc] init];
    myLayer.strokeColor = [[UIColor greenColor] CGColor];
    myLayer.lineWidth = 11.0;
    myLayer.fillColor = nil;
    myLayer.lineJoin = kCALineJoinBevel;
    myLayer.path = pointPath;
    [drawingImgView.layer addSublayer:myLayer];

    CGPathRelease(pointPath);
}

Answer 1

- (void)drawPathWithPoints:(int)xAxis andYaxis:(int)yAxis
{    
    CGSize screenSize = drawingImgView.frame.size;

    UIGraphicsBeginImageContext(drawingImgView.frame.size);

    CGContextRef currentContext = UIGraphicsGetCurrentContext();
     [drawingImgView.image drawInRect:CGRectMake(0, 0, screenSize.width, screenSize.height)];

    CGContextSetLineCap(currentContext, kCGLineCapRound);
    CGContextSetLineWidth(currentContext, 9.0);
    CGContextSetRGBStrokeColor(currentContext, 0, 0, 1, 1);
    CGContextBeginPath(currentContext);



    CGContextMoveToPoint(currentContext,xAxis,yAxis);

     CGContextAddLineToPoint(currentContext, xAxis, yAxis);
            CGContextStrokePath(UIGraphicsGetCurrentContext());

  drawingImgView.image = UIGraphicsGetImageFromCurrentImageContext();

    CGPathRelease(pointPath);
}