iOS开发入门之——拖动视图
预备知识
iOS处理屏幕上的触摸动作，主要涉及到以下几个方法：
touchesBegan:withEvent: //触摸屏幕的最开始被调用
touchesMoved:withEvent: //移动过程中被调用
touchesEnded:withEvent: //动作结束时被调用
touchesCancelled:WithEvent:
从方法的命名可以清晰的看出该方法何时被调用，最后一个比较特殊。touchesCancelled:WithEvent:在Cocoa Touch必须响应持续触摸事件的系统中断时调用。
我们只要重写这些方法，来作我们想要作的事情就可以了。
如何实现拖动视图？
1.设置userInteractionEnabled属性为YES，允许用户交互。
2.在触摸动作开始时记录起始点。
3.在移动过程中，计算当前位置坐标与起始点的差值，即偏移量，并且移动视图中心点至偏移量大小的地方。
4.分别限制x坐标、与y坐标，保证用户不可将视图托出屏幕
备注：分别限制x坐标与y坐标的原因是，即使向右拖动不了了，仍需保证可以向下拖动。
实现代码
以子类化UIImageView为例
#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
#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