Question

我只是在学习核心图形。所以我创建了一个新项目，包括一个UIView类。现在我在我的UIView实现文件中有以下代码

-(id) initWithCoder:(NSCoder*)sourceCoder
{
    if( ( self = [super initWithCoder:sourceCoder]))
    {
        //place any other initialization  here
    }
    return self;
}

- (void)drawRect:(CGRect)rect {

    CGContextRef    context = UIGraphicsGetCurrentContext();

    CGContextSetLineWidth(context,4);
    CGContextSetStrokeColorWithColor(context, myColor.CGColor);


    CGContextMoveToPoint(context,startPoint.x , startPoint.y);
    CGContextAddLineToPoint(context, endPoint.x, endPoint.y);
    CGContextStrokePath(context);

}
- (void) touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event
{
    UITouch* touchPoint = [touches anyObject]; 
    startPoint = [touchPoint locationInView:self];
    endPoint = [touchPoint locationInView:self];

    [self setNeedsDisplay];
}

-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch* touch = [touches anyObject];
    endPoint=[touch locationInView:self];
    [self setNeedsDisplay];
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    UITouch* touch = [touches anyObject];
    endPoint = [touch locationInView:self];
    [self setNeedsDisplay];
}

但它只是创建了一条线，如果我再次尝试绘制，那么前一行就会丢失。

但我想前一行不应该丢失，我该怎么做？

Answer 1

将视图的clearsContextBeforeDrawing property设置为NO。

Answer 2

将UIImageView设置为背景，使用以下内容保存上下文（行）

CGContextStrokePath(UIGraphicsGetCurrentContext());
<your imageView>.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

如何在iPhone屏幕中绘制连续线

2 个答案: