Frame and Bounds of CAShapeLayer

问题:

I am working on CAShapeLayer.And trying to draw non-linear path.I want to set frame to CAShapeLayer.So i can use CGPathGetPathBoundingBox method to get frame from CGPathRef.

Here is code :

CGMutablePathRef path = CGPathCreateMutable();
CGPathAddArc(path, NULL, rect.size.width/2, rect.size.height/2, 100, (0), (M_PI_2), NO);
CGPathAddArc(path, NULL, rect.size.width/2, rect.size.height/2, 100-50, (M_PI_2), (0), YES);
CGPathCloseSubpath(path);
CAShapeLayer* arcLayer = [[CAShapeLayer alloc]init];
arcLayer.path = path;
arcLayer.frame = CGPathGetPathBoundingBox(path);
arcLayer.bounds = CGPathGetPathBoundingBox(path);
[self.layer addSublayer:arcLayer]; ` 

Please refer my code carefully .I have set same frame and bounds to CAShapeLayer.My problem is if i am not setting bounds (same as frame) ,then it wont show my content or it wont show my content within frame.Why?Please help me.Thanking you.

回答1:

When you modify the frame of a CALayer, you are modifying its size and position in the coordinate space of its superlayer. frame is a computed value, based on the object's bounds and position. In this case, the layer does not yet have a superlayer so its coordinate space is dimensionless. When you set the frame, the size gets carried through to the bounds property, but since any point in a dimensionless space is zero, the position will remain zero instead of what you'd intended.

To solve this, you can set the bounds to set the layer's size, and position (which is a real non-computed property) in the coordinate space of the superlayer before adding it as a sublayer.

回答2:

The following is a quote from the CALayer documentation:

The frame rectangle is position and size of the layer specified in the superlayer’s coordinate space. For layers, the frame rectangle is a computed property that is derived from the values in the bounds, anchorPoint and position properties. When you assign a new value to this property, the layer changes its position and bounds properties to match the rectangle you specified. The values of each coordinate in the rectangle are measured in points.

It looks like with the CAShapeLayer when setting the frame by itself it does't keep the origin values from the assigned CGRect, only the size. When you set the bounds the origin is kept and therefore displays in the proper location. You also need to set the position value to the center point of where you want you shape to be displayed:

CGMutablePathRef path = CGPathCreateMutable();
CGPathAddArc(path, NULL, rect.size.width/2, rect.size.height/2, 100, (0), (M_PI_2), NO);
CGPathAddArc(path, NULL, rect.size.width/2, rect.size.height/2, 100-50, (M_PI_2), (0), YES);
CGPathCloseSubpath(path);
CAShapeLayer* arcLayer = [CAShapeLayer layer];
arcLayer.path = path;
CGRect pathRect = CGPathGetPathBoundingBox(path);
arcLayer.bounds = pathRect;
arcLayer.position = CGPointMake(CGRectGetMidX(pathRect), CGRectGetMidY(pathRect));
[self.layer addSublayer:arcLayer];

回答3:

In my experience, setting the position of a CAShapeLayer is completely sufficient for it to show up where you want it. Setting the bounds is not required for this.

See the CoreAnimationText sample code for using it that way.

回答4:

You need to set bounds or else it will behave like the anchorPoint is set to [0, 0]. Who wants that? :D