objective-c - 如何使用 iPhone SDK 只拖动一张图片

Question

我想创建一个可以拍摄两张图片的小应用程序，我只想让图片可以拖动。经过研究，我找到了这个解决方案:

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

    UITouch *touch = [[ event allTouches] anyObject];

    image.alpha = 0.7;

    if([touch view] == image){
        CGPoint location = [touch locationInView:self.view];
        image.center = location;
    }

它有效，但问题是图像可以从其中心拖动，我不希望这样。所以我找到了另一个解决方案:

- (void) touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event { 
    // Retrieve the touch point 
    CGPoint pt = [[touches anyObject] locationInView:self.view]; 
    startLocation = pt; 
    [[self view] bringSubviewToFront:self.view]; 

}


- (void) touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event { 
    // Move relative to the original touch point 

    CGPoint pt = [[touches anyObject] locationInView:self.view]; 
    frame = [self.view frame]; 
    frame.origin.x += pt.x - startLocation.x; 
    frame.origin.y += pt.y - startLocation.y; 
    [self.view setFrame:frame]; 
} 

效果很好，但是当我添加另一张图片时， View 的所有图片都可以同时拖动。我是 iPhone 开发的新手，我不知道如何才能让图像变得可拖动。

Answer 1

你可以在 touchesBegan: 方法中使用 if 条件，看这个-

-(void)ViewDidLoad
{
    //Your First Image View
    UIImageView *imageView1 = [UIImageView alloc]initWithFrame:CGRectMake(150.0, 100.0, 30.0, 30.0)];
    [imageView1 setImage:[UIImage imageNamed:@"anyImage.png"]];
    [imageView1 setUserInteractionEnabled:YES];
    [self.view addSubview:imageView1];

    //Your Second Image View
    UIImageView *imageView2 = [UIImageView alloc]initWithFrame:CGRectMake(150.0, 200.0, 30.0, 30.0)];
    [imageView2 setImage:[UIImage imageNamed:@"anyImage.png"]];
    [imageView2 setUserInteractionEnabled:YES];
    [self.view addSubview:imageView2];
}

//Now Use Touch begin methods with condition like this

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [[event allTouches]anyObject];
    if([touch view] == imageView1)
    {
        CGPoint pt = [[touches anyObject] locationInView:imageView1];
        startLocation = pt;
    }

    if([touch view] == imageView2)
    {
        CGPoint pt = [[touches anyObject] locationInView:imageView2];
        startLocation = pt;
    }
}

//Use same thing with touch move methods...
- (void) touchesMoved:(NSSet *)touches withEvent: (UIEvent *)event 
{
    UITouch *touch = [[event allTouches]anyObject];
    if([touch view] == imageView1)
    {
        CGPoint pt = [[touches anyObject] previousLocationInView:imageView1];
        CGFloat dx = pt.x - startLocation.x;
        CGFloat dy = pt.y - startLocation.y;
        CGPoint newCenter = CGPointMake(imageView1.center.x + dx, imageView1.center.y + dy);
        imageView1.center = newCenter;
    }

    if([touch view] == imageView2)
    {
        CGPoint pt = [[touches anyObject] previousLocationInView:imageView2];
        CGFloat dx = pt.x - startLocation.x;
        CGFloat dy = pt.y - startLocation.y;
        CGPoint newCenter = CGPointMake(imageView2.center.x + dx, imageView2.center.y + dy);
        imageView2.center = newCenter;
    }
}

这两个图像只有在您触摸并移动它时才会移动。希望我的教程对您有所帮助。