了解 CGAffineTransform 交互

Question

我正在尝试制作一个简单的应用程序，其中“固定”的图像在用手指移动后返回到其位置。这可能用代码可以更好地解释：

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
     image.transform = CGAffineTransformIdentity;
}


- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [[event allTouches] anyObject];
    if (CGRectContainsPoint([image frame], [touch locationInView:nil])) 
    {
         image.center = [touch locationInView:nil];
    }
}

- (void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
     if (pin) {
         CGPoint point = image.center;
         CGPoint center = self.view.center;
         //CGAffineTransform transform = CGAffineTransformMakeTranslation(0, 0);
         [UIView beginAnimations:nil context:NULL];
         [UIView setAnimationDuration:0.5];
         image.transform = CGAffineTransformMakeTranslation(center.x - point.x, center.y - point.y);
         //image.transform = CGAffineTransformConcat(image.transform, CGAffineTransformMakeTranslation(center.x - point.x, center.y - point.y));
    [UIView commitAnimations];

    }
}

每次我按下图像时，它都会移动，以便它从我的手指下移出。我认为这与转变有关。有人能指出我正确的方向吗？

Answer 1

我认为你应该使用

image.transform = CGAffineTransformMakeTranslation(difference.x, difference.y);

你这样做的方式，你会在每次迭代 TouchMoved 时积累越来越多的翻译。我认为中心属性不依赖于变换。

Answer 2

编辑

我实际上会这样做：

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
}


- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    CGPoint location = [[touches anyObject] locationInView:[touch view]];
    CGPoint difference = CGPointMake(location.x - image.center.x, location.y - image.center.y);

    image.transform = CGAffineTransformTranslate(image.transform, difference.x, difference.y);
}

- (void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    if (pin) {
        [UIView beginAnimations:nil context:NULL];
        [UIView setAnimationDuration:0.5];
        image.transform = CGAffineTransformIdentity;
        [UIView commitAnimations];
    }
}