我一直在寻找答案几个小时，但找不到有关该主题的任何内容。

我有一个与Objective-
c有关的问题。我正在制作一个应用程序，其中UIView检查用户的触摸，如果用户触摸并移动了他/她的手指，则会绘制使用UIBezierPath的路径。如果用户进行绘制以使路径相交，则路径应从屏幕上消失。当用户绘制完图案后，如果路径中的最后一条线与另一条“线”相交，则路径中最后一点的线应自动与路径中的第一点连接（我正在使用“
closePath”方法）在路径中，路径也应从屏幕上消失。

我将每个触摸点存储在CGPoint中，并将其存储在另一个称为Line的类中，作为Point A和PointB。然后将“ line”保存到名为“
lines”的NSMutableArray中。每次将点添加到路径中时，我都会使用（-（BOOL）checkLineIntersection：（CGPoint）p1方法来检查该点与之前绘制的点之间的线是否与线中的任何“线”相交：（CGPoint）p2：（CGPoint）p3：（CGPoint）p4）我从本教程中获得“
http://www.iossourcecode.com/2012/08/02/how-to-make-a-game-like- cut-the-rope-
part-2 /”。

问题

问题是，当我运行应用程序时，它有时可以工作，但有时在我绘制时，线条与路径相交不会消失。我不知道为什么…当我慢慢画画时，它似乎经常发生。

代码：

MyView.h：

#import <UIKit/UIKit.h>
#import "Line.h"
@interface MyView : UIView {

NSMutableArray *pathArray;
UIBezierPath *myPath;
NSMutableArray *lines;
Line *line;
}

@end

MyView.m：

#import "MyView.h"

@implementation MyView


- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
    // Initialization code
    pathArray=[[NSMutableArray alloc]init];

}
return self;
}

- (void)drawRect:(CGRect)rect
{
[[UIColor redColor] setStroke];
[[UIColor blueColor] setFill];

for (UIBezierPath *_path in pathArray) {
    //[_path fill];

    [_path strokeWithBlendMode:kCGBlendModeNormal alpha:1.0];
}
}

#pragma mark - Touch Methods
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
myPath = [[UIBezierPath alloc]init];
lines = [[NSMutableArray alloc]init];
myPath.lineWidth=1;

UITouch *mytouch = [[event allTouches] anyObject];
[myPath moveToPoint:[mytouch locationInView:mytouch.view]];

[pathArray addObject:myPath];

}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{

if(myPath.isEmpty) {

} else {

    UITouch *mytouch = [[event allTouches] anyObject];
    [myPath addLineToPoint:[mytouch locationInView:mytouch.view]];

    CGPoint pointA = [mytouch previousLocationInView:mytouch.view];
    CGPoint pointB = [mytouch locationInView:mytouch.view];

    line = [[Line alloc]init];
    [line setPointA:pointA];
    [line setPointB:pointB];

    [lines addObject:line];

    for(Line *l in lines) {

        CGPoint pa = l.pointA;
        CGPoint pb = l.pointB;

        //NSLog(@"Point A: %@", NSStringFromCGPoint(pa));
        //NSLog(@"Point B: %@", NSStringFromCGPoint(pb));

        if ([self checkLineIntersection:pointA :pointB :pa :pb])
        {
            [pathArray removeLastObject];
            [myPath removeAllPoints];
            [self setNeedsDisplay];
            NSLog(@"Removed path!");
            return;
        }
    }
}
[self setNeedsDisplay];
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
if(myPath.isEmpty) {


} else if ([lines count] != 0){
    line = [[Line alloc]init];
    line = [lines lastObject];
    CGPoint pointA = line.pointA;
    line = [[Line alloc]init];
    line = [lines objectAtIndex:0];
    CGPoint pointB = line.pointA;

    [myPath closePath];
    for(Line *l in lines) {

        CGPoint pa = l.pointA;
        CGPoint pb = l.pointB;

        if ([self checkLineIntersection:pointA :pointB :pa :pb])
        {
            [pathArray removeLastObject];
            [myPath removeAllPoints];
            [self setNeedsDisplay];
            NSLog(@"Removed path!");
            return;
        }
    } 
}
[self setNeedsDisplay];
}

-(BOOL)checkLineIntersection:(CGPoint)p1 :(CGPoint)p2 :(CGPoint)p3 :(CGPoint)p4
{
CGFloat denominator = (p4.y - p3.y) * (p2.x - p1.x) - (p4.x - p3.x) * (p2.y - p1.y);

/*
// In this case the lines are parallel so you assume they don't intersect
if (denominator == 0.0f)
    return NO;
*/

CGFloat ua = ((p4.x - p3.x) * (p1.y - p3.y) - (p4.y - p3.y) * (p1.x - p3.x)) / denominator;
CGFloat ub = ((p2.x - p1.x) * (p1.y - p3.y) - (p2.y - p1.y) * (p1.x - p3.x)) / denominator;

if (ua > 0.0 && ua < 1.0 && ub > 0.0 && ub < 1.0)
{
    return YES;
}

return NO;
}


@end

Line.h：

#import <UIKit/UIKit.h>

@interface Line : UIView

@property (nonatomic, assign) CGPoint pointA;
@property (nonatomic, assign) CGPoint pointB;

@end

Line.m：

#import "Line.h"

@implementation Line

@synthesize pointA;
@synthesize pointB;

- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self) {
    // Initialization code
}
return self;
}

/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{
// Drawing code
}
*/

@end

我希望有人能够回答这个问题。抱歉，这很明显。先感谢您！