拖动视图

@interface MoveView : UIView
{
    CGPoint startPoint;
}


#import "MoveView.h"

@implementation MoveView

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
        //允许用户交互
        self.userInteractionEnabled = YES;
    }
    return self;
}

- (id)initWithImage:(UIImage *)image
{
    self = [super initWithImage:image];
    if (self) {
        //允许用户交互
        self.userInteractionEnabled = YES;
    }
    return self;
}

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    //保存触摸起始点位置
    CGPoint point = [[touches anyObject] locationInView:self];
    startPoint = point;
    
    //该view置于最前
    [[self superview] bringSubviewToFront:self];
}

-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    //计算位移=当前位置-起始位置
    CGPoint point = [[touches anyObject] locationInView:self];
    float dx = point.x - startPoint.x;
    float dy = point.y - startPoint.y;
    
    //计算移动后的view中心点
    CGPoint newcenter = CGPointMake(self.center.x + dx, self.center.y + dy);
    
    
    /* 限制用户不可将视图托出屏幕 */
    float halfx = CGRectGetMidX(self.bounds);
    //x坐标左边界
    newcenter.x = MAX(halfx, newcenter.x);
    //x坐标右边界
    newcenter.x = MIN(self.superview.bounds.size.width - halfx, newcenter.x);
    
    //y坐标同理
    float halfy = CGRectGetMidY(self.bounds);
    newcenter.y = MAX(halfy, newcenter.y);
    newcenter.y = MIN(self.superview.bounds.size.height - halfy, newcenter.y);
    
    //移动view
    self.center = newcenter;
}

@end