举例讲解iOS开发中拖动视图的实现

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#import <UIKit/UIKit.h> 
 
@interface GragView : UIImageView 
{ 
    CGPoint startPoint; 
} 
@end 

#import "GragView.h" 
 
@implementation GragView 
 
- (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; 
} 
 
/* 
// Only override drawRect: if you perform custom drawing. 
// An empty implementation adversely affects performance during animation. 
- (void)drawRect:(CGRect)rect 
{ 
    // Drawing code 
} 
*/ 
 
@end