鼠标移动划线
PaintView.h

CGPoint lastPoint;
UIImageView *lineImageView;


PaintView.m

- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self)
{
lineImageView = [[UIImageView alloc] initWithFrame:frame];
lineImageView.backgroundColor = [UIColor grayColor];
[self addSubview:lineImageView];
}

return self;
}

- (void)drawRect:(CGRect)rect
{
CGContextRef c = UIGraphicsGetCurrentContext(); // 获取当前的设备上下文，必须在drawRect中获取，否则会出错

CGContextSetLineCap(context, kCGLineCapRound); // 设置划线样式
CGContextSetLineWidth(context, 6);
CGContextSetRGBStrokeColor(context, 0, 0, 0, 1); // 设置画出的线的颜色信息

CGContextBeginPath(context);
CGContextMoveToPoint(context, 10, 10);
CGContextAddLineToPoint(context, 100, 100);

CGContextStrokePath(context); // 绘出图形

[super drawRect:rect];
}

// 移动鼠标划线
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *aTouch = [touches anyObject];
lastPoint = [aTouch locationInView:self];

CGContextSetFillColorWithColor(context, [UIColor redColor].CGColor);
CGContextSetAllowsAntialiasing(context, YES);

CGContextMoveToPoint(context, 0, 15);
CGContextAddEllipseInRect(context, CGRectMake(0, 0, 70, 70));

CGContextDrawPath(context, 1);
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *aTouch = [touches anyObject];

CGPoint currentPoint = [aTouch locationInView:self];

UIGraphicsBeginImageContext(self.frame.size); // 创建一个bitmap设备上下文 如果不创建，UIGraphicsGetCurrentContext()不能获取当前设备上下文


[lineImageView.image drawInRect:CGRectMake(0, 0, 768, 1024)]; // 设置图形的显示区域

CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 7);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 1.0, 1.0, 1.0);

CGContextBeginPath(UIGraphicsGetCurrentContext());

CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());

[lineImageView setImage:UIGraphicsGetImageFromCurrentImageContext()];
UIGraphicsEndImageContext(); // 关闭创建的设备上下文

lastPoint = currentPoint;
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
UIGraphicsBeginImageContext(self.frame.size);
[lineImageView.image drawInRect:CGRectMake(0, 0, 768, 1024)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 7);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 1.0, 1.0, 1.0);
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
CGContextFlush(UIGraphicsGetCurrentContext());
[lineImageView setImage:UIGraphicsGetImageFromCurrentImageContext()];
UIGraphicsEndImageContext();

}