Question

- (void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [[event allTouches] anyObject];
CGPoint endlocation = [touch locationInView:touch.view];
UIImage* thing;
UIImageView* thing2 = [[UIImageView alloc] init];
UIImageView* thing3=[[UIImageView alloc] init];
switch ([_diagramselect selectedSegmentIndex]) {
    case 0:
        thing = [UIImage imageNamed:@"makeO"];
        [thing2 setFrame:CGRectMake(endlocation.x-72,endlocation.y-172,25,25)];
        [thing2 setImage:thing];
        [_field addSubview:thing2];
        break;
    case 1:
        thing = [UIImage imageNamed:@"missX"];
        [thing2 setFrame:CGRectMake(endlocation.x-72,endlocation.y-172,25,25)];
        [thing2 setImage:thing];
        [_field addSubview:thing2];
        break;
    case 2:
        CGContextRef *context = UIGraphicsGetCurrentContext();
        CGContextSetStrokeColor(context,black);
        CGContextBeginPath(context);
        CGContextMoveToPoint(context,startlocation.x,startlocation.y);
        CGContextAddLineToPoint(context,endlocation.x,endlocation.y);
        CGContextStrokePath(context);





        /*thing = [UIImage imageNamed:@"passArrow"];
        [thing3 setFrame:CGRectMake(startlocation.x-72,startlocation.y-172,endlocation.x-startlocation.x,endlocation.y-startlocation.y)];
        [thing3 setImage:thing];
        [_field addSubview:thing3];
      */

        break;
    case 3:
        thing = [UIImage imageNamed:@"trussArrow"];
        break;

    default:
        break;
}

案例2旨在从水龙头的初始位置绘制到水龙头的最终位置。但是，以下代码给出了＆＃34;期望表达式＆＃34;的错误。在CGContextRef的行上，因此以下行不识别上下文。这是什么问题？是否存在此代码需要定位的特定视图，如果是，我将如何执行此操作？谢谢！

Answer 1

尝试不使用指针引用星号：

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetStrokeColor(context,black);
CGContextBeginPath(context);
CGContextMoveToPoint(context,startlocation.x,startlocation.y);
CGContextAddLineToPoint(context,endlocation.x,endlocation.y);
CGContextStrokePath(context);

此外，根据您的目的，您可能需要查看UIGraphicsBeginImageContext()和UIGraphicsEndImageContext()。

如何将CGContext实现到实际代码中？

1 个答案: