UITouches 屏幕绘图
与手势一样，UIView 掌握直接屏幕绘图。当用户触摸屏幕时，Touchview类收集一系列点。在每个触摸移动之处，touchesMoved：WithEvent: 方法调用
setNeedsDispaly。这又会触发对drawRect：调用，其中视图将这些点绘制成线段来创建一个可视屏幕路径。
代码：
#define POINT(X) [[self.points objectAtIndex:X] CGPointValue]
UIColor *current;
@interface TouchView : UIView
{
NSMutableArray *points;
}
@property (retain) NSMutableArray *points;
@end
@implementation TouchView
@synthesize points;
- (BOOL) isMultipleTouchEnabled {return NO;}
// Start new array
- (void) touchesBegan:(NSSet *) touches withEvent:(UIEvent *) event
{
self.points = [NSMutableArray array];
CGPoint pt = [[touches anyObject] locationInView:self];
[self.points addObject:[NSValue valueWithCGPoint:pt]];
}
// Add each point to array
- (void) touchesMoved:(NSSet *) touches withEvent:(UIEvent *) event
{
CGPoint pt = [[touches anyObject] locationInView:self];
[self.points addObject:[NSValue valueWithCGPoint:pt]];
[self setNeedsDisplay];
}
// Draw all points
- (void) drawRect: (CGRect) rect
{
if (!self.points) return;
if (self.points.count < 2) return;
CGContextRef context = UIGraphicsGetCurrentContext();
[current set];
CGContextSetLineWidth(context, 4.0f);
int i = 0;
for ( i;i < (self.points.count - 1); i++)
{
CGPoint pt1 = POINT(i);
CGPoint pt2 = POINT(i+1);
CGContextMoveToPoint(context, pt1.x, pt1.y);
CGContextAddLineToPoint(context, pt2.x, pt2.y);
CGContextStrokePath(context);
}
}
@end
