用手势绘制直线

Question

用手势绘制直线

4

我使用以下代码将一个视图添加为子视图：

    imageview = [[UIImageView alloc] initWithFrame:[holderView frame]];
    [imageview setImage:cppobject->OutputImage];
    imageview.contentMode = UIViewContentModeScaleAspectFit;

    [holderView addSubview:imageview];
    holderView.contentMode = UIViewContentModeScaleAspectFit ;

    UIPinchGestureRecognizer *pinchRecognizer = [[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(scale:)];
    [pinchRecognizer setDelegate:self];
    [holderView addGestureRecognizer:pinchRecognizer];
    [pinchRecognizer release];

    UIRotationGestureRecognizer *rotationRecognizer = [[UIRotationGestureRecognizer alloc] initWithTarget:self action:@selector(rotate:)];
    [rotationRecognizer setDelegate:self];
    [holderView addGestureRecognizer:rotationRecognizer];
    [rotationRecognizer release];

    UIPanGestureRecognizer *panRecognizer = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(move:)];
    [panRecognizer setMinimumNumberOfTouches:1];
    [panRecognizer setMaximumNumberOfTouches:1];
    [panRecognizer setDelegate:self];
    [holderView addGestureRecognizer:panRecognizer];
    [panRecognizer release];

-(void)scale:(id)sender {
}

-(void)rotate:(id)sender {
}

-(void)move:(id)sender {
}

-(void)tapped:(id)sender {
}

当用户使用两个手指滑动时，我需要绘制一条线，并显示一个UILabel（绿色的那个），如下图所示：

我查看了如何在iPhone手势中绘制图形？但我无法将其应用于子视图，特别是DrawInRect方法。

在panRecognizer函数（move）中，我想要使用以下方法绘制线条：

    UIPanGestureRecognizer *gR = (UIPanGestureRecognizer *) sender ; 
    NSValue *value = [NSValue valueWithCGPoint: [gR locationInView:gR.view]]; 
    [Points addObject:value];
    [holderView setNeedsDisplay];

    NSLog(@"End of measuring") ;

我将使用Points中的点来绘制所有子视图上方的线条。

-(void)drawRect:(CGRect)rect { 
  NSLog(@"Entered Draw In Rect");
  if (Measuring) {
    [[UIColor redColor] setStroke];
    UIBezierPath *pathToDraw = [UIBezierPath bezierPath]; 

    for (int n = 1; n < [Points count] - 1 ; n++) { 
      NSValue * value = [Points objectAtIndex:(NSInteger)n];
      CGPoint  point = [value CGPointValue]; 
      [pathToDraw moveToPoint:point];
      value = [Points objectAtIndex:(NSInteger)n+1];
      point = [value CGPointValue];
      [pathToDraw addLineToPoint:point];
    }
    [pathToDraw stroke];
  }
}

问题是[holderView setNeedsDisplay];从未调用或触发drawRect。有关此问题的任何建议或帮助。

有什么建议吗？

- AMH

看起来你的 holderView 可能是一个 UIScrollView。如果是这种情况，那么这会更加困难。你能同时发布你的 drawRect: 方法吗？当我们无法看到相关代码时，帮助你变得非常困难。 - RyanR

我尝试了[imageView setNeedsDisplay]; 但它没有起作用。 - AMH

setNeedsDisplay 只是告诉框架视图需要被渲染。如果视图没有正确插入到层次结构中，drawRect 将不会被调用。 - RyanR

将在另一个视图上绘制的逻辑分离出来！例如，使用类似于imageView的透明MeasurementView，添加imageview的子视图并在那里处理绘制逻辑。@AMH - Mahesh

1个回答

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原文链接

- Matt Connolly · Accepted Answer

图片视图作为子视图，绘制在容器视图之上。图片视图是不透明的。这意味着当视图被绘制时，实际上没有任何部分是可见的，因此它的drawRect调用被优化掉了。

尝试改变视图的顺序，使得容器视图成为图片视图的子视图。然后图片视图将被绘制，而容器视图将绘制在其上方。

另外，请注意应该使用父视图的边界作为子视图的框架。

UIView* subview = [[UIView alloc] initWithFrame:[parentview bounds]];

编辑（添加）：

请参见http://developer.apple.com/library/ios/#documentation/WindowsViews/Conceptual/ViewPG_iPhoneOS/WindowsandViews/WindowsandViews.html%23//apple_ref/doc/uid/TP40009503-CH2-SW1，特别是在“视图层次结构和子视图管理”一节下面：

“从视觉上看，子视图的内容会遮盖其父视图的全部或部分内容。”

因此，请将imageview设置为父视图，并像以下这样进行初始化：

// instance variables:
UIImageView* imageView;
MyHolderView* holderView;

imageView = [[UIImageView alloc] initWithFrame:mainRect];
holderView = [[MyHolderView alloc] initWithFrame:[imageView bounds]];
holderView.opaque = NO;
holderView.backgroundColor = [UIColor clearColor];
[imageView addSubview:holderView];

UIPinchGestureRecognizer *pinchRecognizer = [[UIPinchGestureRecognizer alloc] initWithTarget:holderView action:@selector(scale:)];
[pinchRecognizer setDelegate:self];
[holderView addGestureRecognizer:pinchRecognizer];
[pinchRecognizer release];

// etc...

现在，图像视图已经绘制完成，其子视图保持在其上层。当您在holderview上调用setNeedsDisplay时，它将收到drawRect:调用。

例如，这样跟踪手势。这可以在您的视图控制器或MyHolderView视图子类中完成；此处的示例将在MyHolderView类中完成，以便location1和location2实例变量可以轻松共享给drawRect:方法：

-(void)scale:(id)sender {
  if (sender == pinchRecognizer) { // this allows the responder to work with multiple gestures if required
    // get position of touches, for example:
    NSUInteger num_touches = [pinchRecognizer numberOfTouches];

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

    // tell the view to redraw.
    [holderView setNeedsDisplay];
  }
}

然后在持有者视图的drawRect例程中：

-(void)drawRect:(CGRect)rect {

  // use instance variables location1 and location2 to draw the line.
}