如何將CGContext實現爲實際代碼？

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; 
} 

情況2旨在從水龍頭的初始位置到水龍頭的結束位置。但是下面的代碼在CGContextRef行上給出了「預期表達式」的錯誤，結果下面的行不能識別上下文。這裏有什麼問題？有沒有一個特定的觀點，這個代碼需要針對，如果是的話，我會如何做到這一點？謝謝！

Answer 1

嘗試沒有指針引用星號：

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

此外，你可能想看看這取決於你想做什麼UIGraphicsBeginImageContext()和UIGraphicsEndImageContext()。