ios - Xcode 如何上下移动图像动画

Question

嘿，我正在尝试将 ImageView 向下移动到屏幕中间，然后再回到顶部。这是我的代码，现在它只是移动到中间并留在那里。

-(void)lineGoBack
{
    //move diagonally down
    line.center = CGPointMake(line.center.x,
                              line.center.y-10);
    //start time for first method
    [NSTimer scheduledTimerWithTimeInterval:.5 target:self selector:@selector(LineMovement) userInfo:nil repeats:NO];
}


//The LINE
-(void)LineMovement
{ 
    lineMovementOffset = CGPointMake(line.center.x, screenSizeY/2);

    //move diagonally up
    line.center = CGPointMake(line.center.x,
                              line.center.y+10);

    //start time for second method
    [NSTimer scheduledTimerWithTimeInterval:.5 target:self selector:@selector(lineGoBack) userInfo:nil repeats:NO];
}

Answer 1

我不喜欢将基于 block 的动画用于链式动画——它们往往变得难以阅读。我建议使用 keyframe animations .这也使您能够轻松地为动画定义许多中间点，或者为动画添加更多高级功能，例如曲线。

下面是一个示例，说明如何在三点之间为 UIView 设置线性动画。

CGPoint startPoint = (CGPoint){100.f, 100.f};
CGPoint middlePoint = (CGPoint){400.f, 400.f};
CGPoint endPoint = (CGPoint){600.f, 100.f};

CGMutablePathRef thePath = CGPathCreateMutable();
CGPathMoveToPoint(thePath, NULL, startPoint.x, startPoint.y);
CGPathAddLineToPoint(thePath, NULL, middlePoint.x, middlePoint.y);
CGPathAddLineToPoint(thePath, NULL, endPoint.x, endPoint.y);

CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
animation.duration = 3.f;
animation.path = thePath;
[self.animatedView.layer addAnimation:animation forKey:@"position"];
self.animatedView.layer.position = endPoint;

要在两点之间做无限动画，您可以使用下面的代码。将它应用于 UIImageView 的效果相同。

CGPoint startPoint = (CGPoint){100.f, 100.f};
CGPoint endPoint = (CGPoint){400.f, 400.f};

CGMutablePathRef thePath = CGPathCreateMutable();
CGPathMoveToPoint(thePath, NULL, startPoint.x, startPoint.y);
CGPathAddLineToPoint(thePath, NULL, endPoint.x, endPoint.y);

CAKeyframeAnimation *animation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
animation.duration = 3.f;
animation.path = thePath;
animation.autoreverses = YES;
animation.repeatCount = INFINITY;
[self.animatedView.layer addAnimation:animation forKey:@"position"];