用计时器动画替换 UIview 动画

Question

这是我的代码：

- (CGPoint)randomPointSquare {
CGRect frame = [[self view] frame];

//CGFloat rand_x = ((float)arc4random() / (float)UINT_MAX) * (float)_window.frame.size.width;

NSInteger side = arc4random() / (UINT_MAX/4);
CGFloat offset = 0;

switch(side) {
    case 0: /* top */
        offset = ((float)arc4random() / (float)UINT_MAX) * (float)frame.size.width;
        return CGPointMake(offset, -10);

    case 1: /* bottom */
        offset = ((float)arc4random() / (float)UINT_MAX) * (float)frame.size.width;
        return CGPointMake(offset, frame.size.height-150);

    case 2: /* left */
        offset = ((float)arc4random() / (float)UINT_MAX) * (float)frame.size.height;
        return CGPointMake(-10, offset);

    default:
    case 3: /* right */
        offset = ((float)arc4random() / (float)UINT_MAX) * (float)frame.size.height;
        return CGPointMake(frame.size.width+170, offset);
}
}



-(void)createNewImageView {
UIImage * image = [UIImage imageNamed:@"abouffer_03.png"];
imageView = [[UIImageView alloc] initWithImage:image];


// Add it at a random point
[imageView setCenter:[self randomPointSquare]];
[[self view] addSubview:imageView];

// Animate it into place
[UIView beginAnimations:nil context:nil];
[UIView setAnimationDuration:8.0f];
[imageView setCenter:CGPointMake(240, 160)];
[UIView commitAnimations];
 [imageView release];
}

所以你可以看到有一个 UIView 动画，但现在我想用一个定时器来改变和替换它。但我不知道该怎么做。好吧，如果你知道怎么做，别忘了我希望 imageView 在随机位置创建，然后移动到屏幕中心。谢谢

Answer 1

与其为你编写所有代码，不如给你一些建议，帮助你改变它（我认为这是最好的学习方式）。

首先，当您在对randomPointSqaure 的调用中创建位置时，将创建的点存储为实例变量。

theLocation = [self randomPointSquare];

然后将imageView的位置设置为this

[imageView setCenter:theLocation];

计算对象与您希望的点（240、160）之间的距离，然后除以您希望它移动的时间量。例如，如果您的位置是 (0, 160)，那么它将移动 240 像素。如果您希望超过 10 秒，则为每秒 24 像素。将其保存在实例变量中作为“delta”

现在创建一个调用方法来更新位置的计时器

[NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:@selector(updatePosition) userInfo:nil repeats:YES];

然后创建updatePosition方法

- (void)updatePosition {
    ...
    // Calculate the new position
    // delta is divided by 100 as the timer runs every 0.01 second
    // and delta was calculated previously as being distance per second
    theLocation = theLocation + (delta / 100);
    ...
    [imageView setCenter:theLocation];

    // Check if the location is at the "collision point" and do whatever if it is
    if (theLocation.x == 240 && theLocation.y == 160) {
       // We've hit the "collision point"
    }
}

这应该会给您一些关于如何使用计时器而不是动画的想法。这就是游戏执行相同操作的方式 - 您只需以小步骤更新对象的位置，然后每次检查碰撞等。

Answer 2

我不知道您是想在几秒钟后显示随机设置的图像，还是希望将动画从随机位置移动到中心位置。不管怎样，我把这两个选项都放在这里了

1)

首先，一旦你在下面创建了图像视图调用函数：

-(void)randomlySetImage{
    int x = arc4random() % (int)self.view.frame.size.width;
    int y = arc4random() % (int)self.view.frame.size.height;

   imageView.center = CGPointMake(x,y);

   [NSTimer scheduledTimerWithTimeInterval:1.0f
                                    target:self 
                                  selector:@selector(randomlySetImage) 
                                  userInfo:nil 
                                   repeats:YES];
}

2)

[CATransaction begin];
[CATransaction setValue:[NSNumber numberWithFloat:2.0f] forKey:kCATransactionAnimationDuration];

CAKeyframeAnimation *positionAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
CGMutablePathRef positionPath = CGPathCreateMutable();
CGPathMoveToPoint(positionPath, NULL, randomX ,  randomY );
CGPathAddLineToPoint(positionPath, NULL, self.view.center.x , self.view.center.y);
positionAnimation.path = positionPath;

[[imageView layer] addAnimation:positionAnimation forKey:@"PositionAnimation"];

[CATransaction commit];

希望对你有帮助