只有当你第一次触摸它时才移动的可拖式图像

Question

我正在制作一个游戏，在这个游戏中，你必须将一个图像拖过视图。我目前正在使用此代码来完成以下操作：

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
    UITouch *mytouch = [[event allTouches] anyObject];
    circle.center = [mytouch locationInView:self.view];
    [self collision];
}

上面的代码的问题是，如果图像位于屏幕的右侧，我按下左边，图像将移动到我刚刚触摸到的左侧位置。我希望它是可拖动的，但只有当你首先按下图像，然后拖动它左右移动。因此，您首先必须按下屏幕右侧的图像，然后(将我的手指放在屏幕上)拖动到左边(或者我拖动手指的地方)。

Answer 1

我发现的最简洁的方法是子类UIImageView，然后您所要做的就是：

#import "MyImageView.h"

@implementation MyImageView

- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInView:self.superview];
    self.center = location;
}

@end

用于此的示例ViewController如下所示：

#import "ViewController.h"
#import "MyImageView.h"
#import <QuartzCore/QuartzCore.h>
#define NUM_IMAGES 50

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    const float radius = 15.0f;
    const float diameter = radius * 2;
    for (int i = 0; i < NUM_IMAGES; ++i)
    {
        float x = radius + drand48() * (self.view.frame.size.width - diameter - radius);
        float y = radius + drand48() * (self.view.frame.size.height - diameter - radius);
        MyImageView *imageView = [[MyImageView alloc] initWithFrame:CGRectMake(x, y, diameter, diameter)];
        imageView.backgroundColor = [UIColor colorWithRed:drand48()
                                                    green:drand48()
                                                     blue:drand48()
                                                    alpha:1.0f];
        imageView.userInteractionEnabled = YES;
        imageView.layer.cornerRadius = radius;
        UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(0.f, 0.f, diameter, diameter)];
        label.text = [NSString stringWithFormat:@"%i", i + 1];
        label.textAlignment = NSTextAlignmentCenter;
        [imageView addSubview:label];
        [self.view addSubview:imageView];
    }
}

@end