objective-c - objective-c : making point Larger through long press

Question

是否可以通过长按来画出更大的点？因为我想让我的线条在长按手势时变得更大，并使用该点使触摸中的线条移动。我希望这是有道理的，这是我的代码。

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event//upon moving
{

            UITouch *touch = [touches anyObject];
            previousPoint2 = previousPoint1;
            previousPoint1 = currentTouch;
            currentTouch = [touch locationInView:self.view];


            CGPoint mid1 = midPoint(previousPoint2, previousPoint1); 
            CGPoint mid2 = midPoint(currentTouch, previousPoint1);


            UIGraphicsBeginImageContext(CGSizeMake(1024, 768));
            [imgDraw.image drawInRect:CGRectMake(0, 0, 1024, 768)];
            CGContextRef context = UIGraphicsGetCurrentContext();
            CGContextSetLineCap(context,kCGLineCapRound);
            CGContextSetLineWidth(context, slider.value);
            CGContextSetBlendMode(context, blendMode);
            CGContextSetRGBStrokeColor(context,red, green, blue, 1);
            CGContextBeginPath(context);
            CGContextMoveToPoint(context, mid1.x, mid1.y);//Computation
            CGContextAddQuadCurveToPoint(context, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y);
            CGContextStrokePath(context);

            imgDraw.image = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsGetCurrentContext();
}

现在如何在此处插入长按？

Answer 1

您应该将 UILongPressGestureRecognizer 添加到您的 View 中。然后，该识别器应该有一个与之关联的方法，该方法会增加点的半径，然后绘制它，并在手势结束时将半径重置为某个默认起始值​​。

尝试这样的事情:

-(void)viewDidLoad
{
    [super viewDidLoad];
    UILongPressGestureRecognizer *recognizer = [[UILongPressGestureRecognizer alloc] initWithTarget:self action:@selector(drawAndExpandPoint:)];
    [self addGestureRecognizer:recognizer];
}

然后，在drawAndExpandPoint方法中，您可以执行类似的操作(使用一个名为radius的ivar，它具有一些默认值):

-(void)drawAndExpandPoint:(UILongPressGestureRecognizer *)recognizer
{ 
    //Reset radius, if gesture ended
    if (recognizer.state == UIGestureRecognizerStateEnded) {
        radius = DEFAULT_RADIUS;
        return;
    }

    else if (radius <= MAX_RADIUS) {
        radius += RADIUS_INCREMENT;
        //You will have to write this method to draw the point
        [self drawAtPoint:[recognizer locationInView:self.view] withRadius:radius];
    }
}

这段代码可能不是 100% 你所描述的，但我认为它概述了一般策略，即使用手势识别器 - 它使事情变得更容易。