iPhone: 对象沿路径动画

 

这里我将展示如何在UIView上让对象沿着路径动画，我将创建路径并画到UIView上让你能都看见，并沿相同的路径来做动画。

我在添加到屏幕的UIView完成所有的这些… 

首先，我们在屏幕上画一条曲线

 

//This draws a quadratic bezier curved line right across the screen
- ( void ) drawACurvedLine {
    //Create a bitmap graphics context, you will later get a UIImage from this
    UIGraphicsBeginImageContext(CGSizeMake(320,460));
    CGContextRef ctx = UIGraphicsGetCurrentContext();

    //Set variables in the context for drawing
    CGContextSetLineWidth(ctx, 1.5);
    CGContextSetStrokeColorWithColor(ctx, [UIColor whiteColor].CGColor);

    //Set the start point of your drawing
    CGContextMoveToPoint(ctx, 10, 10);
    //The end point of the line is 310,450 .... i'm also setting a reference point of 10,450
    //A quadratic bezier curve is drawn using these coordinates - experiment and see the results.
    CGContextAddQuadCurveToPoint(ctx, 10, 450, 310, 450);
    //Add another curve, the opposite of the above - finishing back where we started
    CGContextAddQuadCurveToPoint(ctx, 310, 10, 10, 10);

    //Draw the line
    CGContextDrawPath(ctx, kCGPathStroke);

    //Get a UIImage from the current bitmap context we created at the start and then end the image context
    UIImage *curve = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    //With the image, we need a UIImageView
    UIImageView *curveView = [[UIImageView alloc] initWithImage:curve];
    //Set the frame of the view - which is used to position it when we add it to our current UIView
    curveView.frame = CGRectMake(1, 1, 320, 460);
    curveView.backgroundColor = [UIColor clearColor];
    [self addSubview:curveView];
}

 现在我我创建了一个关键帧动画，并添加一个和我们话得线一样的路径。我们还将画一个圈，并沿着路径做动画:

 

- (void) animateCicleAlongPath {
    //Prepare the animation - we use keyframe animation for animations of this complexity
    CAKeyframeAnimation *pathAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    //Set some variables on the animation
    pathAnimation.calculationMode = kCAAnimationPaced;
    //We want the animation to persist - not so important in this case - but kept for clarity
    //If we animated something from left to right - and we wanted it to stay in the new position,
    //then we would need these parameters
    pathAnimation.fillMode = kCAFillModeForwards;
    pathAnimation.removedOnCompletion = NO;
    pathAnimation.duration = 5.0;
    //Lets loop continuously for the demonstration
    pathAnimation.repeatCount = 1000;

    //Setup the path for the animation - this is very similar as the code the draw the line
    //instead of drawing to the graphics context, instead we draw lines on a CGPathRef
    CGPoint endPoint = CGPointMake(310, 450);
    CGMutablePathRef curvedPath = CGPathCreateMutable();
    CGPathMoveToPoint(curvedPath, NULL, 10, 10);
    CGPathAddQuadCurveToPoint(curvedPath, NULL, 10, 450, 310, 450);
    CGPathAddQuadCurveToPoint(curvedPath, NULL, 310, 10, 10, 10);

    //Now we have the path, we tell the animation we want to use this path - then we release the path
    pathAnimation.path = curvedPath;
    CGPathRelease(curvedPath);

    //We will now draw a circle at the start of the path which we will animate to follow the path
    //We use the same technique as before to draw to a bitmap context and then eventually create
    //a UIImageView which we add to our view
    UIGraphicsBeginImageContext(CGSizeMake(20,20));
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    //Set context variables
    CGContextSetLineWidth(ctx, 1.5);
    CGContextSetFillColorWithColor(ctx, [UIColor greenColor].CGColor);
    CGContextSetStrokeColorWithColor(ctx, [UIColor whiteColor].CGColor);
    //Draw a circle - and paint it with a different outline (white) and fill color (green)
    CGContextAddEllipseInRect(ctx, CGRectMake(1, 1, 18, 18));
    CGContextDrawPath(ctx, kCGPathFillStroke);
    UIImage *circle = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    UIImageView *circleView = [[UIImageView alloc] initWithImage:circle];
    circleView.frame = CGRectMake(1, 1, 20, 20);
    [self addSubview:circleView];

    //Add the animation to the circleView - once you add the animation to the layer, the animation starts
    [circleView.layer addAnimation:pathAnimation forKey:@"moveTheSquare"];
}

要让所有的都跑起来，你可以使用init函数：

 

- (id)initWithFrame:(CGRect)frame {
    if (self = [super initWithFrame:frame]) {
        [self drawACurvedLine];
        [self animateCicleAlongPath];
    }
    return self;
}

在你的ViewController中像这样写

 

- (void)viewDidLoad {
    UIView *customView = [[Canvas alloc] initWithFrame:CGRectMake(0, 0, 320, 460)];
    customView.backgroundColor = [UIColor blackColor];
    [self.view addSubview:customView];
    [customView release];
    [super viewDidLoad];
}

还有，不要忘记添加 Quartz 引用:

 

#import <QuartzCore/QuartzCore.h>

我确定有很多更好的方式来做这个事，例如使用CALayers 和添加CGImage 到layers。但是那是一些我没有尝试的东西。上面的例子应该足够让你开始沿着路径做动画。

这里是工程拷贝

 

（译者水平有限，欢迎指正。）