Using drawRect to draw & animate two graphs. A bac

问题:

I am using drawRect to draw a pretty simple shape (dark blue in the image below).

I'd like this to animate from the left to the right, so that it grows. The caveat here is I need there to be a "max" background in gray, as seen in the top part of the image.

Right now, I'm simulating this animation by overlaying a white view, and then animating the size of it, so that it looks like the blue is animating to the right. While this works... I need the background gray shape to always be there. With my overlayed white view, this just doesn't work.

Here's the code for drawing the "current code" version:

    let context = UIGraphicsGetCurrentContext()
    CGContextMoveToPoint(context, 0, self.bounds.height - 6)
    CGContextAddLineToPoint(context, self.bounds.width, 0)
    CGContextAddLineToPoint(context, self.bounds.width, self.bounds.height)
    CGContextAddLineToPoint(context, 0, self.bounds.height)
    CGContextSetFillColorWithColor(context,UIColor(red: 37/255, green: 88/255, blue: 120/255, alpha: 1.0).CGColor)
    CGContextDrawPath(context, CGPathDrawingMode.Fill)

How can I animate the blue part from left to right, while keeping the gray "max" portion of the graph always visible?

回答1:

drawRect is producing still picture. To get animation you're saying about I'd recommend the following:

1. Use CoreAnimation to produce animation
2. Use UIBezierPath to make a shape you need
3. Use CALayer's mask to animate within required shape

Here is example code for Playground:

import UIKit
import QuartzCore
import XCPlayground

let view = UIView(frame: CGRect(x: 0, y: 0, width: 120, height: 40))
XCPlaygroundPage.currentPage.liveView = view

let maskPath = UIBezierPath()

maskPath.moveToPoint(CGPoint(x: 10, y: 30))
maskPath.addLineToPoint(CGPoint(x: 10, y: 25))
maskPath.addLineToPoint(CGPoint(x: 100, y: 10))
maskPath.addLineToPoint(CGPoint(x: 100, y: 30))
maskPath.closePath()

let maskLayer = CAShapeLayer()
maskLayer.path = maskPath.CGPath
maskLayer.fillColor = UIColor.whiteColor().CGColor

let rectToAnimateFrom = UIBezierPath(rect: CGRect(x: 0, y: 0, width: 97, height: 40))
let rectToAnimateTo = UIBezierPath(rect: CGRect(x: 0, y: 0, width: 0, height: 40))

let layerOne = CAShapeLayer()
layerOne.path = maskPath.CGPath
layerOne.fillColor = UIColor.grayColor().CGColor

let layerTwo = CAShapeLayer()
layerTwo.mask = maskLayer
layerTwo.fillColor = UIColor.greenColor().CGColor

view.layer.addSublayer(layerOne)
view.layer.addSublayer(layerTwo)

let animation = CABasicAnimation(keyPath: "path")
animation.fromValue = rectToAnimateFrom.CGPath
animation.toValue = rectToAnimateTo.CGPath
animation.duration = 1
animation.repeatCount = 1000
animation.autoreverses = true

layerTwo.addAnimation(animation, forKey: "Nice animation")

回答2:

In your code, I only see you draw the graphic once, why not draw gray part first and then draw the blue part.

I don't think it is efficient enough to implement animation in drawRect function.

You can take a look at Facebook's Shimmer Example, it simulate the effect of iPhone unlock animation. It uses a mask layer. The idea could also work in your example.

Also, Facebook's pop framework could simplify your work.