了解CGAffineTransform交互

Question

我正在尝试做一个简单的应用程序，在这个应用程序中，一张被“钉住”的图片在被一个手指移动后会返回到原来的位置。这可能用代码解释得更好：

- (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，它就会移动，这样它就会从我的手指下移出来。我认为这与转换有关。有谁能给我指个方向吗？

Answer 1

编辑过的

我实际上是这样做的：

- (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];
    }
}

Answer 2

我觉得你应该直接用

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

你这样做的方式是在touchesMoved的每一次迭代中积累越来越多的翻译。我认为center属性并不依赖于变换。