使用UIPinchGeustureRecognizer绘制线条 [英] Draw Line Using UIPinchGeustureRecognizer

问题描述

我想使用UIPinchGeustureRecognizer绘制线，我已经尝试了所有stackoverflow解决方案，但没有运气。请帮我解决这个问题。我收到以下错误

I want to draw line using UIPinchGeustureRecognizer,I have tried all stackoverflow solution but no luck. please help me to resolve this. I am getting following error

首先我想知道我的代码逻辑是否正确。我没有从touchbegan / touchmoved获得积分。我只从（void）handleLinePinch :( UIPinchGestureRecognizer *）手势获得两分。

First i want to know my code logic is correct or not.and i didnt get the points from touchbegan/touchmoved. i am gettting two points from (void)handleLinePinch:(UIPinchGestureRecognizer *)gesture only.

//My instances in .h file

CGPoint location1,location2;
LineView* l;

- (void)viewDidLoad
{
   [super viewDidLoad];
   l = [[LineView alloc]initWithFrame:self.view.frame];
   [self.view addSubview:l];
   UIPinchGestureRecognizer *linepinch = [[UIPinchGestureRecognizer alloc]    
   initWithTarget:l action:@selector(handleLinePinch:)];
   [l addGestureRecognizer:linepinch];
}


- (void)handleLinePinch:(UIPinchGestureRecognizer *)gesture
{
    NSUInteger num_touches = [gesture numberOfTouches];

    // save locations to some instance variables, like `CGPoint location1, location2;`
    if (num_touches >= 1) {
       location1 = [gesture locationOfTouch:0 inView:l];
    }
    if (num_touches >= 2) {
       location2 = [gesture locationOfTouch:1 inView:l];
    }
    [l drawRect:location1 Loc2:location2];
    [l setNeedsDisplay];

}
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
}


LineView.m

- (void)drawRect:(CGPoint)location1 Loc2:(CGPoint)location2 {

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetLineWidth(context, 5.0);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGFloat components[] = {0.0, 0.0, 1.0, 1.0};
CGColorRef color = CGColorCreate(colorspace, components);
CGContextSetStrokeColorWithColor(context, color);
CGContextMoveToPoint(context, location1.x, location1.y);
CGContextAddLineToPoint(context, location2.x, location2.y);
CGContextStrokePath(context);
CGColorSpaceRelease(colorspace);
CGColorRelease(color);
}

推荐答案

你必须继承 UIView 并覆盖 drawRect：方法，你得到的 CGContextRef UIGraphicsGetCurrentContext 在 drawRect：方法中无效，并且不建立对图形上下文的强引用，因为它可以更改在调用drawRect：方法之间。

You must subclass the UIView and override the drawRect: method, the CGContextRef you get with UIGraphicsGetCurrentContext is invalid out of drawRect: method and don't establish a strong reference to the graphics context because it can change between calls to the drawRect: method.

当您识别到捏合手势时，将CGPoint传递给视图并发送 setNeedsDisplay 方法。

When you recognize the pinch gesture, pass the CGPoint to the view and send setNeedsDisplay method to it.

始终使用 setNeedsDisplay 刷新视图，不要发送 drawRect：直接。

Always use setNeedsDisplay to refresh the view, don't send drawRect: directly.

LineView.m

LineView.m

- (void)drawRect:(CGRect)rect
{
    // p1 and p2 should be set before call `setNeedsDisplay` method
    [self drawRect:location1 Loc2:location2] ;
}

- (void)drawRect:(CGPoint)location1 Loc2:(CGPoint)location2 {
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetLineWidth(context, 5.0);
    CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
    CGFloat components[] = {0.0, 0.0, 1.0, 1.0};
    CGColorRef color = CGColorCreate(colorspace, components);
    CGContextSetStrokeColorWithColor(context, color);
    CGContextMoveToPoint(context, location1.x, location1.y);
    CGContextAddLineToPoint(context, location2.x, location2.y);
    CGContextStrokePath(context);
    CGColorSpaceRelease(colorspace);
    CGColorRelease(color);
}

编辑：我假设您只在两根手指打开时画线。

I assume you only draw the line when two fingers are on.

- (void)handleLinePinch:(UIPinchGestureRecognizer *)gesture
{
    NSUInteger num_touches = [gesture numberOfTouches];

    // save locations to some instance variables, like `CGPoint location1, location2;`
    if (num_touches == 2) {
       location1 = [gesture locationOfTouch:0 inView:l];
       location2 = [gesture locationOfTouch:1 inView:l];
    }
    // you need save location1 and location2 to `l` and refresh `l`.
    // for example: l.location1 = location1; l.location2 = location2;
    [l setNeedsDisplay];

}

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