預備知識
iOS處理屏幕上的觸摸動作,主要涉及到以下幾個方法:
touchesBegan:withEvent: //觸摸屏幕的最開始被調用
touchesMoved:withEvent: //移動過程中被調用
touchesEnded:withEvent: //動作結束時被調用
touchesCancelled:WithEvent:
從方法的命名可以清晰的看出該方法何時被調用,最後一個比較特殊。touchesCancelled:WithEvent:在Cocoa Touch必須響應持續觸摸事件的系統中斷時調用。
我們只要重寫這些方法,來作我們想要作的事情就可以了。
如何實現拖動視圖?
實現代碼
#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
//允許用戶交互
self.userInteractionEnabled = YES;
}
return self;
}
- (id)initWithImage:(UIImage *)image
{
self = [super initWithImage:image];
if (self) {
//允許用戶交互
self.userInteractionEnabled = YES;
}
return self;
}
- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
//保存觸摸起始點位置
CGPoint point = [[touches anyObject] locationInView:self];
startPoint = point;
//該view置於最前
[[self superview] bringSubviewToFront:self];
}
-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
//計算位移=當前位置-起始位置
CGPoint point = [[touches anyObject] locationInView:self];
float dx = point.x - startPoint.x;
float dy = point.y - startPoint.y;
//計算移動後的view中心點
CGPoint newcenter = CGPointMake(self.center.x + dx, self.center.y + dy);
/* 限制用戶不可將視圖托出屏幕 */
float halfx = CGRectGetMidX(self.bounds);
//x座標左邊界
newcenter.x = MAX(halfx, newcenter.x);
//x座標右邊界
newcenter.x = MIN(self.superview.bounds.size.width - halfx, newcenter.x);
//y座標同理
float halfy = CGRectGetMidY(self.bounds);
newcenter.y = MAX(halfy, newcenter.y);
newcenter.y = MIN(self.superview.bounds.size.height - halfy, newcenter.y);
//移動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