我该如何使用两个手指画一条直线,并且在用户拖动或触摸时这条直线仍然可见?我已经尝试过使用核心图形进行简单绘画,但对我来说这似乎有些复杂。
我该如何使用两个手指画一条直线,并且在用户拖动或触摸时这条直线仍然可见?我已经尝试过使用核心图形进行简单绘画,但对我来说这似乎有些复杂。
针对Justin的问题,只需处理touchesBegan
和touchesMoved
。
因此,如果你子类化UIView
,CoreGraphics实现可能如下:
@interface CustomView ()
@property (nonatomic, strong) NSMutableArray *paths;
@property (nonatomic, strong) UIBezierPath *currentPath;
@end
@implementation CustomView
- (id)initWithCoder:(NSCoder *)aDecoder
{
self = [super initWithCoder:aDecoder];
if (self) {
[self setMultipleTouchEnabled:YES];
}
return self;
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
if (!self.currentPath)
{
if (!self.paths)
self.paths = [NSMutableArray array];
self.currentPath = [UIBezierPath bezierPath];
self.currentPath.lineWidth = 3.0;
[self.paths addObject:self.currentPath];
[self touchesMoved:touches withEvent:event];
}
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
if ([touches count] != 2)
return;
[self.currentPath removeAllPoints];
__block NSInteger i = 0;
[touches enumerateObjectsUsingBlock:^(UITouch *touch, BOOL *stop) {
CGPoint location = [touch locationInView:self];
if (i++ == 0)
[self.currentPath moveToPoint:location];
else
[self.currentPath addLineToPoint:location];
}];
[self setNeedsDisplay];
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
self.currentPath = nil;
}
- (void)drawRect:(CGRect)rect
{
[[UIColor redColor] setStroke];
[[UIColor clearColor] setFill];
for (UIBezierPath *path in self.paths)
{
[path stroke];
}
}
- (void)reset
{
self.paths = nil;
[self setNeedsDisplay];
}
@end
另外,您还可以使用Quartz 2D并定义自己的CAShapeLayer
对象,然后您的视图子类或视图控制器可以执行类似以下操作(不用说,这是视图控制器实现;视图实现应该很明显):
#import "ViewController.h"
#import <QuartzCore/QuartzCore.h>
@interface ViewController ()
@property (nonatomic, weak) CAShapeLayer *currentLayer;
@property (nonatomic, strong) UIBezierPath *currentPath;
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
[self.view setMultipleTouchEnabled:YES];
}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
if (!self.currentLayer)
{
CAShapeLayer *layer = [CAShapeLayer layer];
layer.lineWidth = 3.0;
layer.strokeColor = [[UIColor redColor] CGColor];
layer.fillColor = [[UIColor clearColor] CGColor];
[self.view.layer addSublayer:layer];
self.currentLayer = layer;
self.currentPath = [UIBezierPath bezierPath];
[self touchesMoved:touches withEvent:event];
}
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
if ([touches count] != 2)
return;
[self.currentPath removeAllPoints];
__block NSInteger i = 0;
[touches enumerateObjectsUsingBlock:^(UITouch *touch, BOOL *stop) {
CGPoint location = [touch locationInView:self.view];
if (i++ == 0)
[self.currentPath moveToPoint:location];
else
[self.currentPath addLineToPoint:location];
}];
self.currentLayer.path = [self.currentPath CGPath];
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
self.currentPath = nil;
self.currentLayer = nil;
}
- (IBAction)didTouchUpInsideClearButton:(id)sender
{
for (NSInteger i = [self.view.layer.sublayers count] - 1; i >= 0; i--)
{
if ([self.view.layer.sublayers[i] isKindOfClass:[CAShapeLayer class]])
[self.view.layer.sublayers[i] removeFromSuperlayer];
}
}
@end
对于后一种方法,您需要将QuartzCore.framework添加到您的项目中。