iphone - 拖动图像时如何改变alpha值

Question

目标:我希望当我拖动图像时它会变淡以便我们可以看到背景 View 。

我们如何在拖动时增加或减少图像的 alpha 值？

谢谢

Answer 1

我认为您要求的是示例代码。你可以创建一个 UIImageView 的子类。喜欢:

.h

@interface YourImageController : UIImageView
{
    CGPoint startLocation;
}
@end

.m

@implementation YourImageController
- (void) touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {   
    [self setAlpha:x.x];

    // Retrieve the touch point
    CGPoint pt = [[touches anyObject] locationInView:self];
    startLocation = pt;
}

-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    [self setAlpha:x.x];
    CGPoint pt = [[touches anyObject] locationInView:self];
    CGFloat dx = pt.x - startLocation.x;
    CGFloat dy = pt.y - startLocation.y;

    CGPoint newCenter = CGPointMake(self.center.x + dx, self.center.y + dy);

    self.center = newCenter;
}
 -(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
 {
    [self setAlpha:1.0];
 }