如何使用CGMutablePathRef删除已创建的路径？

Question

我根据底部选定的点绘制线条。首先显示从0开始，然后根据所选点显示但是折线图显示之前绘制的线条。

这里我使用的是SHLineGrapgView。这是代码：

- (void)drawPlot:(SHPlot *)plot {

  NSDictionary *theme = plot.plotThemeAttributes;

  //
  CAShapeLayer *backgroundLayer = [CAShapeLayer layer];
  backgroundLayer.frame = self.bounds;
  backgroundLayer.fillColor = [UIColor clearColor].CGColor;
  backgroundLayer.backgroundColor = [UIColor clearColor].CGColor;
  [backgroundLayer setStrokeColor:[UIColor clearColor].CGColor];
  [backgroundLayer setLineWidth:((NSNumber *)theme[kPlotStrokeWidthKey]).intValue];

  CGMutablePathRef backgroundPath= CGPathCreateMutable();
  //
  CAShapeLayer *circleLayer = [CAShapeLayer layer];
  circleLayer.frame = self.bounds;
  circleLayer.fillColor = [UIColor redColor].CGColor;
  circleLayer.backgroundColor = [UIColor clearColor].CGColor;
  [circleLayer setStrokeColor:((UIColor *)theme[kPlotPointFillColorKey]).CGColor];
  [circleLayer setLineWidth:((NSNumber *)theme[kPlotStrokeWidthKey]).intValue];

  CGMutablePathRef circlePath = CGPathCreateMutable();

  //
  CAShapeLayer *graphLayer = [CAShapeLayer layer];
  graphLayer.frame = self.bounds;
  graphLayer.fillColor = [UIColor clearColor].CGColor;
  graphLayer.backgroundColor = [UIColor clearColor].CGColor;
  [graphLayer setStrokeColor:((UIColor *)theme[kPlotStrokeColorKey]).CGColor];
  [graphLayer setLineWidth:((NSNumber *)theme[kPlotStrokeWidthKey]).intValue];

  CGMutablePathRef graphPath = CGPathCreateMutable();


  double yRange = [_yAxisRange doubleValue]; // this value will be in dollars
  double yIntervalValue = yRange / INTERVAL_COUNT;

  //logic to fill the graph path, ciricle path, background path.
    NSLog(@"plottingValues Dictionary %@",plot.plottingValues);

  [plot.plottingValues enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
    NSDictionary *dic = (NSDictionary *)obj;

      NSLog(@"Plotting Dictionary %@",dic);

    __block NSNumber *_key = nil;
    __block NSNumber *_value = nil;

    [dic enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
      _key = (NSNumber *)key;
      _value = (NSNumber *)obj;
    }];

    int xIndex = [self getIndexForValue:_key forPlot:plot];

    //x value
    double height = self.bounds.size.height - BOTTOM_MARGIN_TO_LEAVE;
    double y = height - ((height / ([_yAxisRange doubleValue] + yIntervalValue)) * [_value doubleValue]);
    (plot.xPoints[xIndex]).x = ceil((plot.xPoints[xIndex]).x);
    (plot.xPoints[xIndex]).y = ceil(y);
  }];

  //move to initial point for path and background.
  CGPathMoveToPoint(graphPath, NULL, _leftMarginToLeave, plot.xPoints[0].y);
  CGPathMoveToPoint(backgroundPath, NULL, _leftMarginToLeave, plot.xPoints[0].y);

  int count = (int)_xAxisValues.count;


    for(int i=0; i< count; i++)
  {
      CGPathRef path=CGPathCreateCopy(graphPath);
    CGPoint point = plot.xPoints[i];
     // CGContextRef ref=CGContextCopyPath(<#CGContextRef  _Nullable c#>)
   //   CGContextClip
    CGPathAddLineToPoint(graphPath, NULL, point.x, point.y);
    CGPathAddLineToPoint(backgroundPath, NULL, point.x, point.y);
    CGFloat dotsSize = [_themeAttributes[kDotSizeKey] floatValue];
    CGPathAddEllipseInRect(circlePath, NULL, CGRectMake(point.x - dotsSize/2.0f, point.y - dotsSize/2.0f, dotsSize, dotsSize));
  }

  //move to initial point for path and background.
  CGPathAddLineToPoint(NULL, NULL, _leftMarginToLeave + PLOT_WIDTH, plot.xPoints[count -1].y);
  CGPathAddLineToPoint(backgroundPath, NULL, _leftMarginToLeave + PLOT_WIDTH, plot.xPoints[count - 1].y);

  //additional points for background.
  CGPathAddLineToPoint(backgroundPath, NULL, _leftMarginToLeave + PLOT_WIDTH, self.bounds.size.height - BOTTOM_MARGIN_TO_LEAVE);
  CGPathAddLineToPoint(backgroundPath, NULL, _leftMarginToLeave, self.bounds.size.height - BOTTOM_MARGIN_TO_LEAVE);
  CGPathCloseSubpath(backgroundPath);

  backgroundLayer.path = backgroundPath;
  graphLayer.path = graphPath;
  circleLayer.path = circlePath;

  //animation
  CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"strokeEnd"];
  animation.duration = 1;
  animation.fromValue = @(0.0);
  animation.toValue = @(1.0);
  [graphLayer addAnimation:animation forKey:@"strokeEnd"];

  backgroundLayer.zPosition = 0;
  graphLayer.zPosition = 1;
  circleLayer.zPosition = 2;

  [self.layer addSublayer:graphLayer];
  [self.layer addSublayer:circleLayer];
  [self.layer addSublayer:backgroundLayer];

    NSUInteger count2 = _xAxisValues.count;
    for(int i=0; i< count2; i++){
        CGPoint point = plot.xPoints[i];
        UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom];

        btn.backgroundColor = [UIColor clearColor];
        btn.tag = i;
        btn.frame = CGRectMake(point.x, point.y - 20, 40, 40);
        [btn addTarget:self action:@selector(clicked:) forControlEvents:UIControlEventTouchUpInside];
        objc_setAssociatedObject(btn, kAssociatedPlotObject, plot, OBJC_ASSOCIATION_RETAIN_NONATOMIC);

    [self addSubview:btn];
    }
}